1466 lines
55 KiB
C++
1466 lines
55 KiB
C++
//===- InstCombinePHI.cpp -------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the visitPHINode function.
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//
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//===----------------------------------------------------------------------===//
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#include "InstCombineInternal.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/PatternMatch.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Transforms/InstCombine/InstCombiner.h"
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#include "llvm/Transforms/Utils/Local.h"
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using namespace llvm;
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using namespace llvm::PatternMatch;
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#define DEBUG_TYPE "instcombine"
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static cl::opt<unsigned>
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MaxNumPhis("instcombine-max-num-phis", cl::init(512),
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cl::desc("Maximum number phis to handle in intptr/ptrint folding"));
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STATISTIC(NumPHIsOfInsertValues,
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"Number of phi-of-insertvalue turned into insertvalue-of-phis");
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STATISTIC(NumPHIsOfExtractValues,
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"Number of phi-of-extractvalue turned into extractvalue-of-phi");
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STATISTIC(NumPHICSEs, "Number of PHI's that got CSE'd");
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/// The PHI arguments will be folded into a single operation with a PHI node
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/// as input. The debug location of the single operation will be the merged
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/// locations of the original PHI node arguments.
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void InstCombinerImpl::PHIArgMergedDebugLoc(Instruction *Inst, PHINode &PN) {
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auto *FirstInst = cast<Instruction>(PN.getIncomingValue(0));
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Inst->setDebugLoc(FirstInst->getDebugLoc());
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// We do not expect a CallInst here, otherwise, N-way merging of DebugLoc
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// will be inefficient.
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assert(!isa<CallInst>(Inst));
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for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) {
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auto *I = cast<Instruction>(PN.getIncomingValue(i));
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Inst->applyMergedLocation(Inst->getDebugLoc(), I->getDebugLoc());
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}
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}
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// Replace Integer typed PHI PN if the PHI's value is used as a pointer value.
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// If there is an existing pointer typed PHI that produces the same value as PN,
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// replace PN and the IntToPtr operation with it. Otherwise, synthesize a new
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// PHI node:
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//
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// Case-1:
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// bb1:
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// int_init = PtrToInt(ptr_init)
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// br label %bb2
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// bb2:
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// int_val = PHI([int_init, %bb1], [int_val_inc, %bb2]
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// ptr_val = PHI([ptr_init, %bb1], [ptr_val_inc, %bb2]
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// ptr_val2 = IntToPtr(int_val)
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// ...
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// use(ptr_val2)
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// ptr_val_inc = ...
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// inc_val_inc = PtrToInt(ptr_val_inc)
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//
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// ==>
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// bb1:
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// br label %bb2
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// bb2:
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// ptr_val = PHI([ptr_init, %bb1], [ptr_val_inc, %bb2]
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// ...
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// use(ptr_val)
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// ptr_val_inc = ...
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//
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// Case-2:
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// bb1:
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// int_ptr = BitCast(ptr_ptr)
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// int_init = Load(int_ptr)
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// br label %bb2
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// bb2:
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// int_val = PHI([int_init, %bb1], [int_val_inc, %bb2]
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// ptr_val2 = IntToPtr(int_val)
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// ...
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// use(ptr_val2)
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// ptr_val_inc = ...
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// inc_val_inc = PtrToInt(ptr_val_inc)
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// ==>
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// bb1:
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// ptr_init = Load(ptr_ptr)
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// br label %bb2
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// bb2:
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// ptr_val = PHI([ptr_init, %bb1], [ptr_val_inc, %bb2]
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// ...
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// use(ptr_val)
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// ptr_val_inc = ...
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// ...
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//
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Instruction *InstCombinerImpl::foldIntegerTypedPHI(PHINode &PN) {
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if (!PN.getType()->isIntegerTy())
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return nullptr;
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if (!PN.hasOneUse())
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return nullptr;
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auto *IntToPtr = dyn_cast<IntToPtrInst>(PN.user_back());
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if (!IntToPtr)
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return nullptr;
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// Check if the pointer is actually used as pointer:
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auto HasPointerUse = [](Instruction *IIP) {
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for (User *U : IIP->users()) {
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Value *Ptr = nullptr;
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if (LoadInst *LoadI = dyn_cast<LoadInst>(U)) {
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Ptr = LoadI->getPointerOperand();
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} else if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
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Ptr = SI->getPointerOperand();
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} else if (GetElementPtrInst *GI = dyn_cast<GetElementPtrInst>(U)) {
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Ptr = GI->getPointerOperand();
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}
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if (Ptr && Ptr == IIP)
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return true;
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}
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return false;
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};
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if (!HasPointerUse(IntToPtr))
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return nullptr;
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if (DL.getPointerSizeInBits(IntToPtr->getAddressSpace()) !=
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DL.getTypeSizeInBits(IntToPtr->getOperand(0)->getType()))
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return nullptr;
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SmallVector<Value *, 4> AvailablePtrVals;
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for (unsigned i = 0; i != PN.getNumIncomingValues(); ++i) {
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Value *Arg = PN.getIncomingValue(i);
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// First look backward:
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if (auto *PI = dyn_cast<PtrToIntInst>(Arg)) {
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AvailablePtrVals.emplace_back(PI->getOperand(0));
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continue;
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}
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// Next look forward:
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Value *ArgIntToPtr = nullptr;
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for (User *U : Arg->users()) {
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if (isa<IntToPtrInst>(U) && U->getType() == IntToPtr->getType() &&
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(DT.dominates(cast<Instruction>(U), PN.getIncomingBlock(i)) ||
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cast<Instruction>(U)->getParent() == PN.getIncomingBlock(i))) {
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ArgIntToPtr = U;
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break;
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}
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}
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if (ArgIntToPtr) {
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AvailablePtrVals.emplace_back(ArgIntToPtr);
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continue;
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}
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// If Arg is defined by a PHI, allow it. This will also create
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// more opportunities iteratively.
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if (isa<PHINode>(Arg)) {
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AvailablePtrVals.emplace_back(Arg);
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continue;
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}
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// For a single use integer load:
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auto *LoadI = dyn_cast<LoadInst>(Arg);
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if (!LoadI)
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return nullptr;
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if (!LoadI->hasOneUse())
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return nullptr;
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// Push the integer typed Load instruction into the available
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// value set, and fix it up later when the pointer typed PHI
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// is synthesized.
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AvailablePtrVals.emplace_back(LoadI);
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}
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// Now search for a matching PHI
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auto *BB = PN.getParent();
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assert(AvailablePtrVals.size() == PN.getNumIncomingValues() &&
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"Not enough available ptr typed incoming values");
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PHINode *MatchingPtrPHI = nullptr;
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unsigned NumPhis = 0;
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for (auto II = BB->begin(); II != BB->end(); II++, NumPhis++) {
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// FIXME: consider handling this in AggressiveInstCombine
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PHINode *PtrPHI = dyn_cast<PHINode>(II);
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if (!PtrPHI)
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break;
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if (NumPhis > MaxNumPhis)
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return nullptr;
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if (PtrPHI == &PN || PtrPHI->getType() != IntToPtr->getType())
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continue;
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MatchingPtrPHI = PtrPHI;
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for (unsigned i = 0; i != PtrPHI->getNumIncomingValues(); ++i) {
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if (AvailablePtrVals[i] !=
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PtrPHI->getIncomingValueForBlock(PN.getIncomingBlock(i))) {
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MatchingPtrPHI = nullptr;
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break;
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}
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}
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if (MatchingPtrPHI)
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break;
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}
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if (MatchingPtrPHI) {
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assert(MatchingPtrPHI->getType() == IntToPtr->getType() &&
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"Phi's Type does not match with IntToPtr");
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// The PtrToCast + IntToPtr will be simplified later
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return CastInst::CreateBitOrPointerCast(MatchingPtrPHI,
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IntToPtr->getOperand(0)->getType());
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}
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// If it requires a conversion for every PHI operand, do not do it.
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if (all_of(AvailablePtrVals, [&](Value *V) {
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return (V->getType() != IntToPtr->getType()) || isa<IntToPtrInst>(V);
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}))
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return nullptr;
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// If any of the operand that requires casting is a terminator
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// instruction, do not do it. Similarly, do not do the transform if the value
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// is PHI in a block with no insertion point, for example, a catchswitch
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// block, since we will not be able to insert a cast after the PHI.
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if (any_of(AvailablePtrVals, [&](Value *V) {
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if (V->getType() == IntToPtr->getType())
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return false;
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auto *Inst = dyn_cast<Instruction>(V);
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if (!Inst)
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return false;
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if (Inst->isTerminator())
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return true;
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auto *BB = Inst->getParent();
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if (isa<PHINode>(Inst) && BB->getFirstInsertionPt() == BB->end())
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return true;
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return false;
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}))
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return nullptr;
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PHINode *NewPtrPHI = PHINode::Create(
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IntToPtr->getType(), PN.getNumIncomingValues(), PN.getName() + ".ptr");
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InsertNewInstBefore(NewPtrPHI, PN);
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SmallDenseMap<Value *, Instruction *> Casts;
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for (unsigned i = 0; i != PN.getNumIncomingValues(); ++i) {
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auto *IncomingBB = PN.getIncomingBlock(i);
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auto *IncomingVal = AvailablePtrVals[i];
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if (IncomingVal->getType() == IntToPtr->getType()) {
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NewPtrPHI->addIncoming(IncomingVal, IncomingBB);
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continue;
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}
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#ifndef NDEBUG
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LoadInst *LoadI = dyn_cast<LoadInst>(IncomingVal);
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assert((isa<PHINode>(IncomingVal) ||
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IncomingVal->getType()->isPointerTy() ||
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(LoadI && LoadI->hasOneUse())) &&
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"Can not replace LoadInst with multiple uses");
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#endif
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// Need to insert a BitCast.
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// For an integer Load instruction with a single use, the load + IntToPtr
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// cast will be simplified into a pointer load:
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// %v = load i64, i64* %a.ip, align 8
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// %v.cast = inttoptr i64 %v to float **
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// ==>
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// %v.ptrp = bitcast i64 * %a.ip to float **
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// %v.cast = load float *, float ** %v.ptrp, align 8
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Instruction *&CI = Casts[IncomingVal];
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if (!CI) {
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CI = CastInst::CreateBitOrPointerCast(IncomingVal, IntToPtr->getType(),
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IncomingVal->getName() + ".ptr");
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if (auto *IncomingI = dyn_cast<Instruction>(IncomingVal)) {
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BasicBlock::iterator InsertPos(IncomingI);
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InsertPos++;
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BasicBlock *BB = IncomingI->getParent();
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if (isa<PHINode>(IncomingI))
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InsertPos = BB->getFirstInsertionPt();
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assert(InsertPos != BB->end() && "should have checked above");
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InsertNewInstBefore(CI, *InsertPos);
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} else {
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auto *InsertBB = &IncomingBB->getParent()->getEntryBlock();
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InsertNewInstBefore(CI, *InsertBB->getFirstInsertionPt());
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}
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}
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NewPtrPHI->addIncoming(CI, IncomingBB);
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}
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// The PtrToCast + IntToPtr will be simplified later
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return CastInst::CreateBitOrPointerCast(NewPtrPHI,
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IntToPtr->getOperand(0)->getType());
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}
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/// If we have something like phi [insertvalue(a,b,0), insertvalue(c,d,0)],
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/// turn this into a phi[a,c] and phi[b,d] and a single insertvalue.
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Instruction *
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InstCombinerImpl::foldPHIArgInsertValueInstructionIntoPHI(PHINode &PN) {
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auto *FirstIVI = cast<InsertValueInst>(PN.getIncomingValue(0));
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// Scan to see if all operands are `insertvalue`'s with the same indicies,
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// and all have a single use.
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for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) {
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auto *I = dyn_cast<InsertValueInst>(PN.getIncomingValue(i));
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if (!I || !I->hasOneUser() || I->getIndices() != FirstIVI->getIndices())
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return nullptr;
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}
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// For each operand of an `insertvalue`
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std::array<PHINode *, 2> NewOperands;
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for (int OpIdx : {0, 1}) {
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auto *&NewOperand = NewOperands[OpIdx];
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// Create a new PHI node to receive the values the operand has in each
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// incoming basic block.
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NewOperand = PHINode::Create(
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FirstIVI->getOperand(OpIdx)->getType(), PN.getNumIncomingValues(),
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FirstIVI->getOperand(OpIdx)->getName() + ".pn");
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// And populate each operand's PHI with said values.
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for (auto Incoming : zip(PN.blocks(), PN.incoming_values()))
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NewOperand->addIncoming(
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cast<InsertValueInst>(std::get<1>(Incoming))->getOperand(OpIdx),
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std::get<0>(Incoming));
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InsertNewInstBefore(NewOperand, PN);
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}
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// And finally, create `insertvalue` over the newly-formed PHI nodes.
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auto *NewIVI = InsertValueInst::Create(NewOperands[0], NewOperands[1],
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FirstIVI->getIndices(), PN.getName());
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PHIArgMergedDebugLoc(NewIVI, PN);
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++NumPHIsOfInsertValues;
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return NewIVI;
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}
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/// If we have something like phi [extractvalue(a,0), extractvalue(b,0)],
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/// turn this into a phi[a,b] and a single extractvalue.
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Instruction *
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InstCombinerImpl::foldPHIArgExtractValueInstructionIntoPHI(PHINode &PN) {
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auto *FirstEVI = cast<ExtractValueInst>(PN.getIncomingValue(0));
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// Scan to see if all operands are `extractvalue`'s with the same indicies,
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// and all have a single use.
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for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) {
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auto *I = dyn_cast<ExtractValueInst>(PN.getIncomingValue(i));
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if (!I || !I->hasOneUser() || I->getIndices() != FirstEVI->getIndices() ||
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I->getAggregateOperand()->getType() !=
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FirstEVI->getAggregateOperand()->getType())
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return nullptr;
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}
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// Create a new PHI node to receive the values the aggregate operand has
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// in each incoming basic block.
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auto *NewAggregateOperand = PHINode::Create(
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FirstEVI->getAggregateOperand()->getType(), PN.getNumIncomingValues(),
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FirstEVI->getAggregateOperand()->getName() + ".pn");
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// And populate the PHI with said values.
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for (auto Incoming : zip(PN.blocks(), PN.incoming_values()))
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NewAggregateOperand->addIncoming(
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cast<ExtractValueInst>(std::get<1>(Incoming))->getAggregateOperand(),
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std::get<0>(Incoming));
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InsertNewInstBefore(NewAggregateOperand, PN);
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// And finally, create `extractvalue` over the newly-formed PHI nodes.
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auto *NewEVI = ExtractValueInst::Create(NewAggregateOperand,
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FirstEVI->getIndices(), PN.getName());
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PHIArgMergedDebugLoc(NewEVI, PN);
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++NumPHIsOfExtractValues;
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return NewEVI;
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}
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/// If we have something like phi [add (a,b), add(a,c)] and if a/b/c and the
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/// adds all have a single user, turn this into a phi and a single binop.
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Instruction *InstCombinerImpl::foldPHIArgBinOpIntoPHI(PHINode &PN) {
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Instruction *FirstInst = cast<Instruction>(PN.getIncomingValue(0));
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assert(isa<BinaryOperator>(FirstInst) || isa<CmpInst>(FirstInst));
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unsigned Opc = FirstInst->getOpcode();
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Value *LHSVal = FirstInst->getOperand(0);
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Value *RHSVal = FirstInst->getOperand(1);
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Type *LHSType = LHSVal->getType();
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Type *RHSType = RHSVal->getType();
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// Scan to see if all operands are the same opcode, and all have one user.
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for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) {
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Instruction *I = dyn_cast<Instruction>(PN.getIncomingValue(i));
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if (!I || I->getOpcode() != Opc || !I->hasOneUser() ||
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// Verify type of the LHS matches so we don't fold cmp's of different
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// types.
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I->getOperand(0)->getType() != LHSType ||
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I->getOperand(1)->getType() != RHSType)
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return nullptr;
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// If they are CmpInst instructions, check their predicates
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if (CmpInst *CI = dyn_cast<CmpInst>(I))
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if (CI->getPredicate() != cast<CmpInst>(FirstInst)->getPredicate())
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return nullptr;
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// Keep track of which operand needs a phi node.
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if (I->getOperand(0) != LHSVal) LHSVal = nullptr;
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if (I->getOperand(1) != RHSVal) RHSVal = nullptr;
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}
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// If both LHS and RHS would need a PHI, don't do this transformation,
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// because it would increase the number of PHIs entering the block,
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// which leads to higher register pressure. This is especially
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// bad when the PHIs are in the header of a loop.
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if (!LHSVal && !RHSVal)
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return nullptr;
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// Otherwise, this is safe to transform!
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Value *InLHS = FirstInst->getOperand(0);
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Value *InRHS = FirstInst->getOperand(1);
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PHINode *NewLHS = nullptr, *NewRHS = nullptr;
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if (!LHSVal) {
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NewLHS = PHINode::Create(LHSType, PN.getNumIncomingValues(),
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FirstInst->getOperand(0)->getName() + ".pn");
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NewLHS->addIncoming(InLHS, PN.getIncomingBlock(0));
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InsertNewInstBefore(NewLHS, PN);
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LHSVal = NewLHS;
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}
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if (!RHSVal) {
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NewRHS = PHINode::Create(RHSType, PN.getNumIncomingValues(),
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FirstInst->getOperand(1)->getName() + ".pn");
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NewRHS->addIncoming(InRHS, PN.getIncomingBlock(0));
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InsertNewInstBefore(NewRHS, PN);
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RHSVal = NewRHS;
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}
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// Add all operands to the new PHIs.
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if (NewLHS || NewRHS) {
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for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
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Instruction *InInst = cast<Instruction>(PN.getIncomingValue(i));
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if (NewLHS) {
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Value *NewInLHS = InInst->getOperand(0);
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NewLHS->addIncoming(NewInLHS, PN.getIncomingBlock(i));
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}
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if (NewRHS) {
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Value *NewInRHS = InInst->getOperand(1);
|
|
NewRHS->addIncoming(NewInRHS, PN.getIncomingBlock(i));
|
|
}
|
|
}
|
|
}
|
|
|
|
if (CmpInst *CIOp = dyn_cast<CmpInst>(FirstInst)) {
|
|
CmpInst *NewCI = CmpInst::Create(CIOp->getOpcode(), CIOp->getPredicate(),
|
|
LHSVal, RHSVal);
|
|
PHIArgMergedDebugLoc(NewCI, PN);
|
|
return NewCI;
|
|
}
|
|
|
|
BinaryOperator *BinOp = cast<BinaryOperator>(FirstInst);
|
|
BinaryOperator *NewBinOp =
|
|
BinaryOperator::Create(BinOp->getOpcode(), LHSVal, RHSVal);
|
|
|
|
NewBinOp->copyIRFlags(PN.getIncomingValue(0));
|
|
|
|
for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i)
|
|
NewBinOp->andIRFlags(PN.getIncomingValue(i));
|
|
|
|
PHIArgMergedDebugLoc(NewBinOp, PN);
|
|
return NewBinOp;
|
|
}
|
|
|
|
Instruction *InstCombinerImpl::foldPHIArgGEPIntoPHI(PHINode &PN) {
|
|
GetElementPtrInst *FirstInst =cast<GetElementPtrInst>(PN.getIncomingValue(0));
|
|
|
|
SmallVector<Value*, 16> FixedOperands(FirstInst->op_begin(),
|
|
FirstInst->op_end());
|
|
// This is true if all GEP bases are allocas and if all indices into them are
|
|
// constants.
|
|
bool AllBasePointersAreAllocas = true;
|
|
|
|
// We don't want to replace this phi if the replacement would require
|
|
// more than one phi, which leads to higher register pressure. This is
|
|
// especially bad when the PHIs are in the header of a loop.
|
|
bool NeededPhi = false;
|
|
|
|
bool AllInBounds = true;
|
|
|
|
// Scan to see if all operands are the same opcode, and all have one user.
|
|
for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) {
|
|
GetElementPtrInst *GEP =
|
|
dyn_cast<GetElementPtrInst>(PN.getIncomingValue(i));
|
|
if (!GEP || !GEP->hasOneUser() || GEP->getType() != FirstInst->getType() ||
|
|
GEP->getNumOperands() != FirstInst->getNumOperands())
|
|
return nullptr;
|
|
|
|
AllInBounds &= GEP->isInBounds();
|
|
|
|
// Keep track of whether or not all GEPs are of alloca pointers.
|
|
if (AllBasePointersAreAllocas &&
|
|
(!isa<AllocaInst>(GEP->getOperand(0)) ||
|
|
!GEP->hasAllConstantIndices()))
|
|
AllBasePointersAreAllocas = false;
|
|
|
|
// Compare the operand lists.
|
|
for (unsigned op = 0, e = FirstInst->getNumOperands(); op != e; ++op) {
|
|
if (FirstInst->getOperand(op) == GEP->getOperand(op))
|
|
continue;
|
|
|
|
// Don't merge two GEPs when two operands differ (introducing phi nodes)
|
|
// if one of the PHIs has a constant for the index. The index may be
|
|
// substantially cheaper to compute for the constants, so making it a
|
|
// variable index could pessimize the path. This also handles the case
|
|
// for struct indices, which must always be constant.
|
|
if (isa<ConstantInt>(FirstInst->getOperand(op)) ||
|
|
isa<ConstantInt>(GEP->getOperand(op)))
|
|
return nullptr;
|
|
|
|
if (FirstInst->getOperand(op)->getType() !=GEP->getOperand(op)->getType())
|
|
return nullptr;
|
|
|
|
// If we already needed a PHI for an earlier operand, and another operand
|
|
// also requires a PHI, we'd be introducing more PHIs than we're
|
|
// eliminating, which increases register pressure on entry to the PHI's
|
|
// block.
|
|
if (NeededPhi)
|
|
return nullptr;
|
|
|
|
FixedOperands[op] = nullptr; // Needs a PHI.
|
|
NeededPhi = true;
|
|
}
|
|
}
|
|
|
|
// If all of the base pointers of the PHI'd GEPs are from allocas, don't
|
|
// bother doing this transformation. At best, this will just save a bit of
|
|
// offset calculation, but all the predecessors will have to materialize the
|
|
// stack address into a register anyway. We'd actually rather *clone* the
|
|
// load up into the predecessors so that we have a load of a gep of an alloca,
|
|
// which can usually all be folded into the load.
|
|
if (AllBasePointersAreAllocas)
|
|
return nullptr;
|
|
|
|
// Otherwise, this is safe to transform. Insert PHI nodes for each operand
|
|
// that is variable.
|
|
SmallVector<PHINode*, 16> OperandPhis(FixedOperands.size());
|
|
|
|
bool HasAnyPHIs = false;
|
|
for (unsigned i = 0, e = FixedOperands.size(); i != e; ++i) {
|
|
if (FixedOperands[i]) continue; // operand doesn't need a phi.
|
|
Value *FirstOp = FirstInst->getOperand(i);
|
|
PHINode *NewPN = PHINode::Create(FirstOp->getType(), e,
|
|
FirstOp->getName()+".pn");
|
|
InsertNewInstBefore(NewPN, PN);
|
|
|
|
NewPN->addIncoming(FirstOp, PN.getIncomingBlock(0));
|
|
OperandPhis[i] = NewPN;
|
|
FixedOperands[i] = NewPN;
|
|
HasAnyPHIs = true;
|
|
}
|
|
|
|
|
|
// Add all operands to the new PHIs.
|
|
if (HasAnyPHIs) {
|
|
for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
|
|
GetElementPtrInst *InGEP =cast<GetElementPtrInst>(PN.getIncomingValue(i));
|
|
BasicBlock *InBB = PN.getIncomingBlock(i);
|
|
|
|
for (unsigned op = 0, e = OperandPhis.size(); op != e; ++op)
|
|
if (PHINode *OpPhi = OperandPhis[op])
|
|
OpPhi->addIncoming(InGEP->getOperand(op), InBB);
|
|
}
|
|
}
|
|
|
|
Value *Base = FixedOperands[0];
|
|
GetElementPtrInst *NewGEP =
|
|
GetElementPtrInst::Create(FirstInst->getSourceElementType(), Base,
|
|
makeArrayRef(FixedOperands).slice(1));
|
|
if (AllInBounds) NewGEP->setIsInBounds();
|
|
PHIArgMergedDebugLoc(NewGEP, PN);
|
|
return NewGEP;
|
|
}
|
|
|
|
/// Return true if we know that it is safe to sink the load out of the block
|
|
/// that defines it. This means that it must be obvious the value of the load is
|
|
/// not changed from the point of the load to the end of the block it is in.
|
|
///
|
|
/// Finally, it is safe, but not profitable, to sink a load targeting a
|
|
/// non-address-taken alloca. Doing so will cause us to not promote the alloca
|
|
/// to a register.
|
|
static bool isSafeAndProfitableToSinkLoad(LoadInst *L) {
|
|
BasicBlock::iterator BBI = L->getIterator(), E = L->getParent()->end();
|
|
|
|
for (++BBI; BBI != E; ++BBI)
|
|
if (BBI->mayWriteToMemory()) {
|
|
// Calls that only access inaccessible memory do not block sinking the
|
|
// load.
|
|
if (auto *CB = dyn_cast<CallBase>(BBI))
|
|
if (CB->onlyAccessesInaccessibleMemory())
|
|
continue;
|
|
return false;
|
|
}
|
|
|
|
// Check for non-address taken alloca. If not address-taken already, it isn't
|
|
// profitable to do this xform.
|
|
if (AllocaInst *AI = dyn_cast<AllocaInst>(L->getOperand(0))) {
|
|
bool isAddressTaken = false;
|
|
for (User *U : AI->users()) {
|
|
if (isa<LoadInst>(U)) continue;
|
|
if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
|
|
// If storing TO the alloca, then the address isn't taken.
|
|
if (SI->getOperand(1) == AI) continue;
|
|
}
|
|
isAddressTaken = true;
|
|
break;
|
|
}
|
|
|
|
if (!isAddressTaken && AI->isStaticAlloca())
|
|
return false;
|
|
}
|
|
|
|
// If this load is a load from a GEP with a constant offset from an alloca,
|
|
// then we don't want to sink it. In its present form, it will be
|
|
// load [constant stack offset]. Sinking it will cause us to have to
|
|
// materialize the stack addresses in each predecessor in a register only to
|
|
// do a shared load from register in the successor.
|
|
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(L->getOperand(0)))
|
|
if (AllocaInst *AI = dyn_cast<AllocaInst>(GEP->getOperand(0)))
|
|
if (AI->isStaticAlloca() && GEP->hasAllConstantIndices())
|
|
return false;
|
|
|
|
return true;
|
|
}
|
|
|
|
Instruction *InstCombinerImpl::foldPHIArgLoadIntoPHI(PHINode &PN) {
|
|
LoadInst *FirstLI = cast<LoadInst>(PN.getIncomingValue(0));
|
|
|
|
// FIXME: This is overconservative; this transform is allowed in some cases
|
|
// for atomic operations.
|
|
if (FirstLI->isAtomic())
|
|
return nullptr;
|
|
|
|
// When processing loads, we need to propagate two bits of information to the
|
|
// sunk load: whether it is volatile, and what its alignment is. We currently
|
|
// don't sink loads when some have their alignment specified and some don't.
|
|
// visitLoadInst will propagate an alignment onto the load when TD is around,
|
|
// and if TD isn't around, we can't handle the mixed case.
|
|
bool isVolatile = FirstLI->isVolatile();
|
|
Align LoadAlignment = FirstLI->getAlign();
|
|
unsigned LoadAddrSpace = FirstLI->getPointerAddressSpace();
|
|
|
|
// We can't sink the load if the loaded value could be modified between the
|
|
// load and the PHI.
|
|
if (FirstLI->getParent() != PN.getIncomingBlock(0) ||
|
|
!isSafeAndProfitableToSinkLoad(FirstLI))
|
|
return nullptr;
|
|
|
|
// If the PHI is of volatile loads and the load block has multiple
|
|
// successors, sinking it would remove a load of the volatile value from
|
|
// the path through the other successor.
|
|
if (isVolatile &&
|
|
FirstLI->getParent()->getTerminator()->getNumSuccessors() != 1)
|
|
return nullptr;
|
|
|
|
// Check to see if all arguments are the same operation.
|
|
for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
|
|
LoadInst *LI = dyn_cast<LoadInst>(PN.getIncomingValue(i));
|
|
if (!LI || !LI->hasOneUser())
|
|
return nullptr;
|
|
|
|
// We can't sink the load if the loaded value could be modified between
|
|
// the load and the PHI.
|
|
if (LI->isVolatile() != isVolatile ||
|
|
LI->getParent() != PN.getIncomingBlock(i) ||
|
|
LI->getPointerAddressSpace() != LoadAddrSpace ||
|
|
!isSafeAndProfitableToSinkLoad(LI))
|
|
return nullptr;
|
|
|
|
LoadAlignment = std::min(LoadAlignment, Align(LI->getAlign()));
|
|
|
|
// If the PHI is of volatile loads and the load block has multiple
|
|
// successors, sinking it would remove a load of the volatile value from
|
|
// the path through the other successor.
|
|
if (isVolatile &&
|
|
LI->getParent()->getTerminator()->getNumSuccessors() != 1)
|
|
return nullptr;
|
|
}
|
|
|
|
// Okay, they are all the same operation. Create a new PHI node of the
|
|
// correct type, and PHI together all of the LHS's of the instructions.
|
|
PHINode *NewPN = PHINode::Create(FirstLI->getOperand(0)->getType(),
|
|
PN.getNumIncomingValues(),
|
|
PN.getName()+".in");
|
|
|
|
Value *InVal = FirstLI->getOperand(0);
|
|
NewPN->addIncoming(InVal, PN.getIncomingBlock(0));
|
|
LoadInst *NewLI =
|
|
new LoadInst(FirstLI->getType(), NewPN, "", isVolatile, LoadAlignment);
|
|
|
|
unsigned KnownIDs[] = {
|
|
LLVMContext::MD_tbaa,
|
|
LLVMContext::MD_range,
|
|
LLVMContext::MD_invariant_load,
|
|
LLVMContext::MD_alias_scope,
|
|
LLVMContext::MD_noalias,
|
|
LLVMContext::MD_nonnull,
|
|
LLVMContext::MD_align,
|
|
LLVMContext::MD_dereferenceable,
|
|
LLVMContext::MD_dereferenceable_or_null,
|
|
LLVMContext::MD_access_group,
|
|
};
|
|
|
|
for (unsigned ID : KnownIDs)
|
|
NewLI->setMetadata(ID, FirstLI->getMetadata(ID));
|
|
|
|
// Add all operands to the new PHI and combine TBAA metadata.
|
|
for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
|
|
LoadInst *LI = cast<LoadInst>(PN.getIncomingValue(i));
|
|
combineMetadata(NewLI, LI, KnownIDs, true);
|
|
Value *NewInVal = LI->getOperand(0);
|
|
if (NewInVal != InVal)
|
|
InVal = nullptr;
|
|
NewPN->addIncoming(NewInVal, PN.getIncomingBlock(i));
|
|
}
|
|
|
|
if (InVal) {
|
|
// The new PHI unions all of the same values together. This is really
|
|
// common, so we handle it intelligently here for compile-time speed.
|
|
NewLI->setOperand(0, InVal);
|
|
delete NewPN;
|
|
} else {
|
|
InsertNewInstBefore(NewPN, PN);
|
|
}
|
|
|
|
// If this was a volatile load that we are merging, make sure to loop through
|
|
// and mark all the input loads as non-volatile. If we don't do this, we will
|
|
// insert a new volatile load and the old ones will not be deletable.
|
|
if (isVolatile)
|
|
for (Value *IncValue : PN.incoming_values())
|
|
cast<LoadInst>(IncValue)->setVolatile(false);
|
|
|
|
PHIArgMergedDebugLoc(NewLI, PN);
|
|
return NewLI;
|
|
}
|
|
|
|
/// TODO: This function could handle other cast types, but then it might
|
|
/// require special-casing a cast from the 'i1' type. See the comment in
|
|
/// FoldPHIArgOpIntoPHI() about pessimizing illegal integer types.
|
|
Instruction *InstCombinerImpl::foldPHIArgZextsIntoPHI(PHINode &Phi) {
|
|
// We cannot create a new instruction after the PHI if the terminator is an
|
|
// EHPad because there is no valid insertion point.
|
|
if (Instruction *TI = Phi.getParent()->getTerminator())
|
|
if (TI->isEHPad())
|
|
return nullptr;
|
|
|
|
// Early exit for the common case of a phi with two operands. These are
|
|
// handled elsewhere. See the comment below where we check the count of zexts
|
|
// and constants for more details.
|
|
unsigned NumIncomingValues = Phi.getNumIncomingValues();
|
|
if (NumIncomingValues < 3)
|
|
return nullptr;
|
|
|
|
// Find the narrower type specified by the first zext.
|
|
Type *NarrowType = nullptr;
|
|
for (Value *V : Phi.incoming_values()) {
|
|
if (auto *Zext = dyn_cast<ZExtInst>(V)) {
|
|
NarrowType = Zext->getSrcTy();
|
|
break;
|
|
}
|
|
}
|
|
if (!NarrowType)
|
|
return nullptr;
|
|
|
|
// Walk the phi operands checking that we only have zexts or constants that
|
|
// we can shrink for free. Store the new operands for the new phi.
|
|
SmallVector<Value *, 4> NewIncoming;
|
|
unsigned NumZexts = 0;
|
|
unsigned NumConsts = 0;
|
|
for (Value *V : Phi.incoming_values()) {
|
|
if (auto *Zext = dyn_cast<ZExtInst>(V)) {
|
|
// All zexts must be identical and have one user.
|
|
if (Zext->getSrcTy() != NarrowType || !Zext->hasOneUser())
|
|
return nullptr;
|
|
NewIncoming.push_back(Zext->getOperand(0));
|
|
NumZexts++;
|
|
} else if (auto *C = dyn_cast<Constant>(V)) {
|
|
// Make sure that constants can fit in the new type.
|
|
Constant *Trunc = ConstantExpr::getTrunc(C, NarrowType);
|
|
if (ConstantExpr::getZExt(Trunc, C->getType()) != C)
|
|
return nullptr;
|
|
NewIncoming.push_back(Trunc);
|
|
NumConsts++;
|
|
} else {
|
|
// If it's not a cast or a constant, bail out.
|
|
return nullptr;
|
|
}
|
|
}
|
|
|
|
// The more common cases of a phi with no constant operands or just one
|
|
// variable operand are handled by FoldPHIArgOpIntoPHI() and foldOpIntoPhi()
|
|
// respectively. foldOpIntoPhi() wants to do the opposite transform that is
|
|
// performed here. It tries to replicate a cast in the phi operand's basic
|
|
// block to expose other folding opportunities. Thus, InstCombine will
|
|
// infinite loop without this check.
|
|
if (NumConsts == 0 || NumZexts < 2)
|
|
return nullptr;
|
|
|
|
// All incoming values are zexts or constants that are safe to truncate.
|
|
// Create a new phi node of the narrow type, phi together all of the new
|
|
// operands, and zext the result back to the original type.
|
|
PHINode *NewPhi = PHINode::Create(NarrowType, NumIncomingValues,
|
|
Phi.getName() + ".shrunk");
|
|
for (unsigned i = 0; i != NumIncomingValues; ++i)
|
|
NewPhi->addIncoming(NewIncoming[i], Phi.getIncomingBlock(i));
|
|
|
|
InsertNewInstBefore(NewPhi, Phi);
|
|
return CastInst::CreateZExtOrBitCast(NewPhi, Phi.getType());
|
|
}
|
|
|
|
/// If all operands to a PHI node are the same "unary" operator and they all are
|
|
/// only used by the PHI, PHI together their inputs, and do the operation once,
|
|
/// to the result of the PHI.
|
|
Instruction *InstCombinerImpl::foldPHIArgOpIntoPHI(PHINode &PN) {
|
|
// We cannot create a new instruction after the PHI if the terminator is an
|
|
// EHPad because there is no valid insertion point.
|
|
if (Instruction *TI = PN.getParent()->getTerminator())
|
|
if (TI->isEHPad())
|
|
return nullptr;
|
|
|
|
Instruction *FirstInst = cast<Instruction>(PN.getIncomingValue(0));
|
|
|
|
if (isa<GetElementPtrInst>(FirstInst))
|
|
return foldPHIArgGEPIntoPHI(PN);
|
|
if (isa<LoadInst>(FirstInst))
|
|
return foldPHIArgLoadIntoPHI(PN);
|
|
if (isa<InsertValueInst>(FirstInst))
|
|
return foldPHIArgInsertValueInstructionIntoPHI(PN);
|
|
if (isa<ExtractValueInst>(FirstInst))
|
|
return foldPHIArgExtractValueInstructionIntoPHI(PN);
|
|
|
|
// Scan the instruction, looking for input operations that can be folded away.
|
|
// If all input operands to the phi are the same instruction (e.g. a cast from
|
|
// the same type or "+42") we can pull the operation through the PHI, reducing
|
|
// code size and simplifying code.
|
|
Constant *ConstantOp = nullptr;
|
|
Type *CastSrcTy = nullptr;
|
|
|
|
if (isa<CastInst>(FirstInst)) {
|
|
CastSrcTy = FirstInst->getOperand(0)->getType();
|
|
|
|
// Be careful about transforming integer PHIs. We don't want to pessimize
|
|
// the code by turning an i32 into an i1293.
|
|
if (PN.getType()->isIntegerTy() && CastSrcTy->isIntegerTy()) {
|
|
if (!shouldChangeType(PN.getType(), CastSrcTy))
|
|
return nullptr;
|
|
}
|
|
} else if (isa<BinaryOperator>(FirstInst) || isa<CmpInst>(FirstInst)) {
|
|
// Can fold binop, compare or shift here if the RHS is a constant,
|
|
// otherwise call FoldPHIArgBinOpIntoPHI.
|
|
ConstantOp = dyn_cast<Constant>(FirstInst->getOperand(1));
|
|
if (!ConstantOp)
|
|
return foldPHIArgBinOpIntoPHI(PN);
|
|
} else {
|
|
return nullptr; // Cannot fold this operation.
|
|
}
|
|
|
|
// Check to see if all arguments are the same operation.
|
|
for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
|
|
Instruction *I = dyn_cast<Instruction>(PN.getIncomingValue(i));
|
|
if (!I || !I->hasOneUser() || !I->isSameOperationAs(FirstInst))
|
|
return nullptr;
|
|
if (CastSrcTy) {
|
|
if (I->getOperand(0)->getType() != CastSrcTy)
|
|
return nullptr; // Cast operation must match.
|
|
} else if (I->getOperand(1) != ConstantOp) {
|
|
return nullptr;
|
|
}
|
|
}
|
|
|
|
// Okay, they are all the same operation. Create a new PHI node of the
|
|
// correct type, and PHI together all of the LHS's of the instructions.
|
|
PHINode *NewPN = PHINode::Create(FirstInst->getOperand(0)->getType(),
|
|
PN.getNumIncomingValues(),
|
|
PN.getName()+".in");
|
|
|
|
Value *InVal = FirstInst->getOperand(0);
|
|
NewPN->addIncoming(InVal, PN.getIncomingBlock(0));
|
|
|
|
// Add all operands to the new PHI.
|
|
for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
|
|
Value *NewInVal = cast<Instruction>(PN.getIncomingValue(i))->getOperand(0);
|
|
if (NewInVal != InVal)
|
|
InVal = nullptr;
|
|
NewPN->addIncoming(NewInVal, PN.getIncomingBlock(i));
|
|
}
|
|
|
|
Value *PhiVal;
|
|
if (InVal) {
|
|
// The new PHI unions all of the same values together. This is really
|
|
// common, so we handle it intelligently here for compile-time speed.
|
|
PhiVal = InVal;
|
|
delete NewPN;
|
|
} else {
|
|
InsertNewInstBefore(NewPN, PN);
|
|
PhiVal = NewPN;
|
|
}
|
|
|
|
// Insert and return the new operation.
|
|
if (CastInst *FirstCI = dyn_cast<CastInst>(FirstInst)) {
|
|
CastInst *NewCI = CastInst::Create(FirstCI->getOpcode(), PhiVal,
|
|
PN.getType());
|
|
PHIArgMergedDebugLoc(NewCI, PN);
|
|
return NewCI;
|
|
}
|
|
|
|
if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(FirstInst)) {
|
|
BinOp = BinaryOperator::Create(BinOp->getOpcode(), PhiVal, ConstantOp);
|
|
BinOp->copyIRFlags(PN.getIncomingValue(0));
|
|
|
|
for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i)
|
|
BinOp->andIRFlags(PN.getIncomingValue(i));
|
|
|
|
PHIArgMergedDebugLoc(BinOp, PN);
|
|
return BinOp;
|
|
}
|
|
|
|
CmpInst *CIOp = cast<CmpInst>(FirstInst);
|
|
CmpInst *NewCI = CmpInst::Create(CIOp->getOpcode(), CIOp->getPredicate(),
|
|
PhiVal, ConstantOp);
|
|
PHIArgMergedDebugLoc(NewCI, PN);
|
|
return NewCI;
|
|
}
|
|
|
|
/// Return true if this PHI node is only used by a PHI node cycle that is dead.
|
|
static bool DeadPHICycle(PHINode *PN,
|
|
SmallPtrSetImpl<PHINode*> &PotentiallyDeadPHIs) {
|
|
if (PN->use_empty()) return true;
|
|
if (!PN->hasOneUse()) return false;
|
|
|
|
// Remember this node, and if we find the cycle, return.
|
|
if (!PotentiallyDeadPHIs.insert(PN).second)
|
|
return true;
|
|
|
|
// Don't scan crazily complex things.
|
|
if (PotentiallyDeadPHIs.size() == 16)
|
|
return false;
|
|
|
|
if (PHINode *PU = dyn_cast<PHINode>(PN->user_back()))
|
|
return DeadPHICycle(PU, PotentiallyDeadPHIs);
|
|
|
|
return false;
|
|
}
|
|
|
|
/// Return true if this phi node is always equal to NonPhiInVal.
|
|
/// This happens with mutually cyclic phi nodes like:
|
|
/// z = some value; x = phi (y, z); y = phi (x, z)
|
|
static bool PHIsEqualValue(PHINode *PN, Value *NonPhiInVal,
|
|
SmallPtrSetImpl<PHINode*> &ValueEqualPHIs) {
|
|
// See if we already saw this PHI node.
|
|
if (!ValueEqualPHIs.insert(PN).second)
|
|
return true;
|
|
|
|
// Don't scan crazily complex things.
|
|
if (ValueEqualPHIs.size() == 16)
|
|
return false;
|
|
|
|
// Scan the operands to see if they are either phi nodes or are equal to
|
|
// the value.
|
|
for (Value *Op : PN->incoming_values()) {
|
|
if (PHINode *OpPN = dyn_cast<PHINode>(Op)) {
|
|
if (!PHIsEqualValue(OpPN, NonPhiInVal, ValueEqualPHIs))
|
|
return false;
|
|
} else if (Op != NonPhiInVal)
|
|
return false;
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
/// Return an existing non-zero constant if this phi node has one, otherwise
|
|
/// return constant 1.
|
|
static ConstantInt *GetAnyNonZeroConstInt(PHINode &PN) {
|
|
assert(isa<IntegerType>(PN.getType()) && "Expect only integer type phi");
|
|
for (Value *V : PN.operands())
|
|
if (auto *ConstVA = dyn_cast<ConstantInt>(V))
|
|
if (!ConstVA->isZero())
|
|
return ConstVA;
|
|
return ConstantInt::get(cast<IntegerType>(PN.getType()), 1);
|
|
}
|
|
|
|
namespace {
|
|
struct PHIUsageRecord {
|
|
unsigned PHIId; // The ID # of the PHI (something determinstic to sort on)
|
|
unsigned Shift; // The amount shifted.
|
|
Instruction *Inst; // The trunc instruction.
|
|
|
|
PHIUsageRecord(unsigned pn, unsigned Sh, Instruction *User)
|
|
: PHIId(pn), Shift(Sh), Inst(User) {}
|
|
|
|
bool operator<(const PHIUsageRecord &RHS) const {
|
|
if (PHIId < RHS.PHIId) return true;
|
|
if (PHIId > RHS.PHIId) return false;
|
|
if (Shift < RHS.Shift) return true;
|
|
if (Shift > RHS.Shift) return false;
|
|
return Inst->getType()->getPrimitiveSizeInBits() <
|
|
RHS.Inst->getType()->getPrimitiveSizeInBits();
|
|
}
|
|
};
|
|
|
|
struct LoweredPHIRecord {
|
|
PHINode *PN; // The PHI that was lowered.
|
|
unsigned Shift; // The amount shifted.
|
|
unsigned Width; // The width extracted.
|
|
|
|
LoweredPHIRecord(PHINode *pn, unsigned Sh, Type *Ty)
|
|
: PN(pn), Shift(Sh), Width(Ty->getPrimitiveSizeInBits()) {}
|
|
|
|
// Ctor form used by DenseMap.
|
|
LoweredPHIRecord(PHINode *pn, unsigned Sh)
|
|
: PN(pn), Shift(Sh), Width(0) {}
|
|
};
|
|
} // namespace
|
|
|
|
namespace llvm {
|
|
template<>
|
|
struct DenseMapInfo<LoweredPHIRecord> {
|
|
static inline LoweredPHIRecord getEmptyKey() {
|
|
return LoweredPHIRecord(nullptr, 0);
|
|
}
|
|
static inline LoweredPHIRecord getTombstoneKey() {
|
|
return LoweredPHIRecord(nullptr, 1);
|
|
}
|
|
static unsigned getHashValue(const LoweredPHIRecord &Val) {
|
|
return DenseMapInfo<PHINode*>::getHashValue(Val.PN) ^ (Val.Shift>>3) ^
|
|
(Val.Width>>3);
|
|
}
|
|
static bool isEqual(const LoweredPHIRecord &LHS,
|
|
const LoweredPHIRecord &RHS) {
|
|
return LHS.PN == RHS.PN && LHS.Shift == RHS.Shift &&
|
|
LHS.Width == RHS.Width;
|
|
}
|
|
};
|
|
} // namespace llvm
|
|
|
|
|
|
/// This is an integer PHI and we know that it has an illegal type: see if it is
|
|
/// only used by trunc or trunc(lshr) operations. If so, we split the PHI into
|
|
/// the various pieces being extracted. This sort of thing is introduced when
|
|
/// SROA promotes an aggregate to large integer values.
|
|
///
|
|
/// TODO: The user of the trunc may be an bitcast to float/double/vector or an
|
|
/// inttoptr. We should produce new PHIs in the right type.
|
|
///
|
|
Instruction *InstCombinerImpl::SliceUpIllegalIntegerPHI(PHINode &FirstPhi) {
|
|
// PHIUsers - Keep track of all of the truncated values extracted from a set
|
|
// of PHIs, along with their offset. These are the things we want to rewrite.
|
|
SmallVector<PHIUsageRecord, 16> PHIUsers;
|
|
|
|
// PHIs are often mutually cyclic, so we keep track of a whole set of PHI
|
|
// nodes which are extracted from. PHIsToSlice is a set we use to avoid
|
|
// revisiting PHIs, PHIsInspected is a ordered list of PHIs that we need to
|
|
// check the uses of (to ensure they are all extracts).
|
|
SmallVector<PHINode*, 8> PHIsToSlice;
|
|
SmallPtrSet<PHINode*, 8> PHIsInspected;
|
|
|
|
PHIsToSlice.push_back(&FirstPhi);
|
|
PHIsInspected.insert(&FirstPhi);
|
|
|
|
for (unsigned PHIId = 0; PHIId != PHIsToSlice.size(); ++PHIId) {
|
|
PHINode *PN = PHIsToSlice[PHIId];
|
|
|
|
// Scan the input list of the PHI. If any input is an invoke, and if the
|
|
// input is defined in the predecessor, then we won't be split the critical
|
|
// edge which is required to insert a truncate. Because of this, we have to
|
|
// bail out.
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
InvokeInst *II = dyn_cast<InvokeInst>(PN->getIncomingValue(i));
|
|
if (!II) continue;
|
|
if (II->getParent() != PN->getIncomingBlock(i))
|
|
continue;
|
|
|
|
// If we have a phi, and if it's directly in the predecessor, then we have
|
|
// a critical edge where we need to put the truncate. Since we can't
|
|
// split the edge in instcombine, we have to bail out.
|
|
return nullptr;
|
|
}
|
|
|
|
for (User *U : PN->users()) {
|
|
Instruction *UserI = cast<Instruction>(U);
|
|
|
|
// If the user is a PHI, inspect its uses recursively.
|
|
if (PHINode *UserPN = dyn_cast<PHINode>(UserI)) {
|
|
if (PHIsInspected.insert(UserPN).second)
|
|
PHIsToSlice.push_back(UserPN);
|
|
continue;
|
|
}
|
|
|
|
// Truncates are always ok.
|
|
if (isa<TruncInst>(UserI)) {
|
|
PHIUsers.push_back(PHIUsageRecord(PHIId, 0, UserI));
|
|
continue;
|
|
}
|
|
|
|
// Otherwise it must be a lshr which can only be used by one trunc.
|
|
if (UserI->getOpcode() != Instruction::LShr ||
|
|
!UserI->hasOneUse() || !isa<TruncInst>(UserI->user_back()) ||
|
|
!isa<ConstantInt>(UserI->getOperand(1)))
|
|
return nullptr;
|
|
|
|
// Bail on out of range shifts.
|
|
unsigned SizeInBits = UserI->getType()->getScalarSizeInBits();
|
|
if (cast<ConstantInt>(UserI->getOperand(1))->getValue().uge(SizeInBits))
|
|
return nullptr;
|
|
|
|
unsigned Shift = cast<ConstantInt>(UserI->getOperand(1))->getZExtValue();
|
|
PHIUsers.push_back(PHIUsageRecord(PHIId, Shift, UserI->user_back()));
|
|
}
|
|
}
|
|
|
|
// If we have no users, they must be all self uses, just nuke the PHI.
|
|
if (PHIUsers.empty())
|
|
return replaceInstUsesWith(FirstPhi, UndefValue::get(FirstPhi.getType()));
|
|
|
|
// If this phi node is transformable, create new PHIs for all the pieces
|
|
// extracted out of it. First, sort the users by their offset and size.
|
|
array_pod_sort(PHIUsers.begin(), PHIUsers.end());
|
|
|
|
LLVM_DEBUG(dbgs() << "SLICING UP PHI: " << FirstPhi << '\n';
|
|
for (unsigned i = 1, e = PHIsToSlice.size(); i != e; ++i) dbgs()
|
|
<< "AND USER PHI #" << i << ": " << *PHIsToSlice[i] << '\n';);
|
|
|
|
// PredValues - This is a temporary used when rewriting PHI nodes. It is
|
|
// hoisted out here to avoid construction/destruction thrashing.
|
|
DenseMap<BasicBlock*, Value*> PredValues;
|
|
|
|
// ExtractedVals - Each new PHI we introduce is saved here so we don't
|
|
// introduce redundant PHIs.
|
|
DenseMap<LoweredPHIRecord, PHINode*> ExtractedVals;
|
|
|
|
for (unsigned UserI = 0, UserE = PHIUsers.size(); UserI != UserE; ++UserI) {
|
|
unsigned PHIId = PHIUsers[UserI].PHIId;
|
|
PHINode *PN = PHIsToSlice[PHIId];
|
|
unsigned Offset = PHIUsers[UserI].Shift;
|
|
Type *Ty = PHIUsers[UserI].Inst->getType();
|
|
|
|
PHINode *EltPHI;
|
|
|
|
// If we've already lowered a user like this, reuse the previously lowered
|
|
// value.
|
|
if ((EltPHI = ExtractedVals[LoweredPHIRecord(PN, Offset, Ty)]) == nullptr) {
|
|
|
|
// Otherwise, Create the new PHI node for this user.
|
|
EltPHI = PHINode::Create(Ty, PN->getNumIncomingValues(),
|
|
PN->getName()+".off"+Twine(Offset), PN);
|
|
assert(EltPHI->getType() != PN->getType() &&
|
|
"Truncate didn't shrink phi?");
|
|
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
BasicBlock *Pred = PN->getIncomingBlock(i);
|
|
Value *&PredVal = PredValues[Pred];
|
|
|
|
// If we already have a value for this predecessor, reuse it.
|
|
if (PredVal) {
|
|
EltPHI->addIncoming(PredVal, Pred);
|
|
continue;
|
|
}
|
|
|
|
// Handle the PHI self-reuse case.
|
|
Value *InVal = PN->getIncomingValue(i);
|
|
if (InVal == PN) {
|
|
PredVal = EltPHI;
|
|
EltPHI->addIncoming(PredVal, Pred);
|
|
continue;
|
|
}
|
|
|
|
if (PHINode *InPHI = dyn_cast<PHINode>(PN)) {
|
|
// If the incoming value was a PHI, and if it was one of the PHIs we
|
|
// already rewrote it, just use the lowered value.
|
|
if (Value *Res = ExtractedVals[LoweredPHIRecord(InPHI, Offset, Ty)]) {
|
|
PredVal = Res;
|
|
EltPHI->addIncoming(PredVal, Pred);
|
|
continue;
|
|
}
|
|
}
|
|
|
|
// Otherwise, do an extract in the predecessor.
|
|
Builder.SetInsertPoint(Pred->getTerminator());
|
|
Value *Res = InVal;
|
|
if (Offset)
|
|
Res = Builder.CreateLShr(Res, ConstantInt::get(InVal->getType(),
|
|
Offset), "extract");
|
|
Res = Builder.CreateTrunc(Res, Ty, "extract.t");
|
|
PredVal = Res;
|
|
EltPHI->addIncoming(Res, Pred);
|
|
|
|
// If the incoming value was a PHI, and if it was one of the PHIs we are
|
|
// rewriting, we will ultimately delete the code we inserted. This
|
|
// means we need to revisit that PHI to make sure we extract out the
|
|
// needed piece.
|
|
if (PHINode *OldInVal = dyn_cast<PHINode>(PN->getIncomingValue(i)))
|
|
if (PHIsInspected.count(OldInVal)) {
|
|
unsigned RefPHIId =
|
|
find(PHIsToSlice, OldInVal) - PHIsToSlice.begin();
|
|
PHIUsers.push_back(PHIUsageRecord(RefPHIId, Offset,
|
|
cast<Instruction>(Res)));
|
|
++UserE;
|
|
}
|
|
}
|
|
PredValues.clear();
|
|
|
|
LLVM_DEBUG(dbgs() << " Made element PHI for offset " << Offset << ": "
|
|
<< *EltPHI << '\n');
|
|
ExtractedVals[LoweredPHIRecord(PN, Offset, Ty)] = EltPHI;
|
|
}
|
|
|
|
// Replace the use of this piece with the PHI node.
|
|
replaceInstUsesWith(*PHIUsers[UserI].Inst, EltPHI);
|
|
}
|
|
|
|
// Replace all the remaining uses of the PHI nodes (self uses and the lshrs)
|
|
// with undefs.
|
|
Value *Undef = UndefValue::get(FirstPhi.getType());
|
|
for (unsigned i = 1, e = PHIsToSlice.size(); i != e; ++i)
|
|
replaceInstUsesWith(*PHIsToSlice[i], Undef);
|
|
return replaceInstUsesWith(FirstPhi, Undef);
|
|
}
|
|
|
|
static Value *SimplifyUsingControlFlow(InstCombiner &Self, PHINode &PN,
|
|
const DominatorTree &DT) {
|
|
// Simplify the following patterns:
|
|
// if (cond)
|
|
// / \
|
|
// ... ...
|
|
// \ /
|
|
// phi [true] [false]
|
|
if (!PN.getType()->isIntegerTy(1))
|
|
return nullptr;
|
|
|
|
if (PN.getNumOperands() != 2)
|
|
return nullptr;
|
|
|
|
// Make sure all inputs are constants.
|
|
if (!all_of(PN.operands(), [](Value *V) { return isa<ConstantInt>(V); }))
|
|
return nullptr;
|
|
|
|
BasicBlock *BB = PN.getParent();
|
|
// Do not bother with unreachable instructions.
|
|
if (!DT.isReachableFromEntry(BB))
|
|
return nullptr;
|
|
|
|
// Same inputs.
|
|
if (PN.getOperand(0) == PN.getOperand(1))
|
|
return PN.getOperand(0);
|
|
|
|
BasicBlock *TruePred = nullptr, *FalsePred = nullptr;
|
|
for (auto *Pred : predecessors(BB)) {
|
|
auto *Input = cast<ConstantInt>(PN.getIncomingValueForBlock(Pred));
|
|
if (Input->isAllOnesValue())
|
|
TruePred = Pred;
|
|
else
|
|
FalsePred = Pred;
|
|
}
|
|
assert(TruePred && FalsePred && "Must be!");
|
|
|
|
// Check which edge of the dominator dominates the true input. If it is the
|
|
// false edge, we should invert the condition.
|
|
auto *IDom = DT.getNode(BB)->getIDom()->getBlock();
|
|
auto *BI = dyn_cast<BranchInst>(IDom->getTerminator());
|
|
if (!BI || BI->isUnconditional())
|
|
return nullptr;
|
|
|
|
// Check that edges outgoing from the idom's terminators dominate respective
|
|
// inputs of the Phi.
|
|
BasicBlockEdge TrueOutEdge(IDom, BI->getSuccessor(0));
|
|
BasicBlockEdge FalseOutEdge(IDom, BI->getSuccessor(1));
|
|
|
|
BasicBlockEdge TrueIncEdge(TruePred, BB);
|
|
BasicBlockEdge FalseIncEdge(FalsePred, BB);
|
|
|
|
auto *Cond = BI->getCondition();
|
|
if (DT.dominates(TrueOutEdge, TrueIncEdge) &&
|
|
DT.dominates(FalseOutEdge, FalseIncEdge))
|
|
// This Phi is actually equivalent to branching condition of IDom.
|
|
return Cond;
|
|
else if (DT.dominates(TrueOutEdge, FalseIncEdge) &&
|
|
DT.dominates(FalseOutEdge, TrueIncEdge)) {
|
|
// This Phi is actually opposite to branching condition of IDom. We invert
|
|
// the condition that will potentially open up some opportunities for
|
|
// sinking.
|
|
auto InsertPt = BB->getFirstInsertionPt();
|
|
if (InsertPt != BB->end()) {
|
|
Self.Builder.SetInsertPoint(&*InsertPt);
|
|
return Self.Builder.CreateNot(Cond);
|
|
}
|
|
}
|
|
|
|
return nullptr;
|
|
}
|
|
|
|
// PHINode simplification
|
|
//
|
|
Instruction *InstCombinerImpl::visitPHINode(PHINode &PN) {
|
|
if (Value *V = SimplifyInstruction(&PN, SQ.getWithInstruction(&PN)))
|
|
return replaceInstUsesWith(PN, V);
|
|
|
|
if (Instruction *Result = foldPHIArgZextsIntoPHI(PN))
|
|
return Result;
|
|
|
|
// If all PHI operands are the same operation, pull them through the PHI,
|
|
// reducing code size.
|
|
if (isa<Instruction>(PN.getIncomingValue(0)) &&
|
|
isa<Instruction>(PN.getIncomingValue(1)) &&
|
|
cast<Instruction>(PN.getIncomingValue(0))->getOpcode() ==
|
|
cast<Instruction>(PN.getIncomingValue(1))->getOpcode() &&
|
|
PN.getIncomingValue(0)->hasOneUser())
|
|
if (Instruction *Result = foldPHIArgOpIntoPHI(PN))
|
|
return Result;
|
|
|
|
// If this is a trivial cycle in the PHI node graph, remove it. Basically, if
|
|
// this PHI only has a single use (a PHI), and if that PHI only has one use (a
|
|
// PHI)... break the cycle.
|
|
if (PN.hasOneUse()) {
|
|
if (Instruction *Result = foldIntegerTypedPHI(PN))
|
|
return Result;
|
|
|
|
Instruction *PHIUser = cast<Instruction>(PN.user_back());
|
|
if (PHINode *PU = dyn_cast<PHINode>(PHIUser)) {
|
|
SmallPtrSet<PHINode*, 16> PotentiallyDeadPHIs;
|
|
PotentiallyDeadPHIs.insert(&PN);
|
|
if (DeadPHICycle(PU, PotentiallyDeadPHIs))
|
|
return replaceInstUsesWith(PN, UndefValue::get(PN.getType()));
|
|
}
|
|
|
|
// If this phi has a single use, and if that use just computes a value for
|
|
// the next iteration of a loop, delete the phi. This occurs with unused
|
|
// induction variables, e.g. "for (int j = 0; ; ++j);". Detecting this
|
|
// common case here is good because the only other things that catch this
|
|
// are induction variable analysis (sometimes) and ADCE, which is only run
|
|
// late.
|
|
if (PHIUser->hasOneUse() &&
|
|
(isa<BinaryOperator>(PHIUser) || isa<GetElementPtrInst>(PHIUser)) &&
|
|
PHIUser->user_back() == &PN) {
|
|
return replaceInstUsesWith(PN, UndefValue::get(PN.getType()));
|
|
}
|
|
// When a PHI is used only to be compared with zero, it is safe to replace
|
|
// an incoming value proved as known nonzero with any non-zero constant.
|
|
// For example, in the code below, the incoming value %v can be replaced
|
|
// with any non-zero constant based on the fact that the PHI is only used to
|
|
// be compared with zero and %v is a known non-zero value:
|
|
// %v = select %cond, 1, 2
|
|
// %p = phi [%v, BB] ...
|
|
// icmp eq, %p, 0
|
|
auto *CmpInst = dyn_cast<ICmpInst>(PHIUser);
|
|
// FIXME: To be simple, handle only integer type for now.
|
|
if (CmpInst && isa<IntegerType>(PN.getType()) && CmpInst->isEquality() &&
|
|
match(CmpInst->getOperand(1), m_Zero())) {
|
|
ConstantInt *NonZeroConst = nullptr;
|
|
bool MadeChange = false;
|
|
for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
|
|
Instruction *CtxI = PN.getIncomingBlock(i)->getTerminator();
|
|
Value *VA = PN.getIncomingValue(i);
|
|
if (isKnownNonZero(VA, DL, 0, &AC, CtxI, &DT)) {
|
|
if (!NonZeroConst)
|
|
NonZeroConst = GetAnyNonZeroConstInt(PN);
|
|
|
|
if (NonZeroConst != VA) {
|
|
replaceOperand(PN, i, NonZeroConst);
|
|
MadeChange = true;
|
|
}
|
|
}
|
|
}
|
|
if (MadeChange)
|
|
return &PN;
|
|
}
|
|
}
|
|
|
|
// We sometimes end up with phi cycles that non-obviously end up being the
|
|
// same value, for example:
|
|
// z = some value; x = phi (y, z); y = phi (x, z)
|
|
// where the phi nodes don't necessarily need to be in the same block. Do a
|
|
// quick check to see if the PHI node only contains a single non-phi value, if
|
|
// so, scan to see if the phi cycle is actually equal to that value.
|
|
{
|
|
unsigned InValNo = 0, NumIncomingVals = PN.getNumIncomingValues();
|
|
// Scan for the first non-phi operand.
|
|
while (InValNo != NumIncomingVals &&
|
|
isa<PHINode>(PN.getIncomingValue(InValNo)))
|
|
++InValNo;
|
|
|
|
if (InValNo != NumIncomingVals) {
|
|
Value *NonPhiInVal = PN.getIncomingValue(InValNo);
|
|
|
|
// Scan the rest of the operands to see if there are any conflicts, if so
|
|
// there is no need to recursively scan other phis.
|
|
for (++InValNo; InValNo != NumIncomingVals; ++InValNo) {
|
|
Value *OpVal = PN.getIncomingValue(InValNo);
|
|
if (OpVal != NonPhiInVal && !isa<PHINode>(OpVal))
|
|
break;
|
|
}
|
|
|
|
// If we scanned over all operands, then we have one unique value plus
|
|
// phi values. Scan PHI nodes to see if they all merge in each other or
|
|
// the value.
|
|
if (InValNo == NumIncomingVals) {
|
|
SmallPtrSet<PHINode*, 16> ValueEqualPHIs;
|
|
if (PHIsEqualValue(&PN, NonPhiInVal, ValueEqualPHIs))
|
|
return replaceInstUsesWith(PN, NonPhiInVal);
|
|
}
|
|
}
|
|
}
|
|
|
|
// If there are multiple PHIs, sort their operands so that they all list
|
|
// the blocks in the same order. This will help identical PHIs be eliminated
|
|
// by other passes. Other passes shouldn't depend on this for correctness
|
|
// however.
|
|
PHINode *FirstPN = cast<PHINode>(PN.getParent()->begin());
|
|
if (&PN != FirstPN)
|
|
for (unsigned i = 0, e = FirstPN->getNumIncomingValues(); i != e; ++i) {
|
|
BasicBlock *BBA = PN.getIncomingBlock(i);
|
|
BasicBlock *BBB = FirstPN->getIncomingBlock(i);
|
|
if (BBA != BBB) {
|
|
Value *VA = PN.getIncomingValue(i);
|
|
unsigned j = PN.getBasicBlockIndex(BBB);
|
|
Value *VB = PN.getIncomingValue(j);
|
|
PN.setIncomingBlock(i, BBB);
|
|
PN.setIncomingValue(i, VB);
|
|
PN.setIncomingBlock(j, BBA);
|
|
PN.setIncomingValue(j, VA);
|
|
// NOTE: Instcombine normally would want us to "return &PN" if we
|
|
// modified any of the operands of an instruction. However, since we
|
|
// aren't adding or removing uses (just rearranging them) we don't do
|
|
// this in this case.
|
|
}
|
|
}
|
|
|
|
// Is there an identical PHI node in this basic block?
|
|
for (PHINode &IdenticalPN : PN.getParent()->phis()) {
|
|
// Ignore the PHI node itself.
|
|
if (&IdenticalPN == &PN)
|
|
continue;
|
|
// Note that even though we've just canonicalized this PHI, due to the
|
|
// worklist visitation order, there are no guarantess that *every* PHI
|
|
// has been canonicalized, so we can't just compare operands ranges.
|
|
if (!PN.isIdenticalToWhenDefined(&IdenticalPN))
|
|
continue;
|
|
// Just use that PHI instead then.
|
|
++NumPHICSEs;
|
|
return replaceInstUsesWith(PN, &IdenticalPN);
|
|
}
|
|
|
|
// If this is an integer PHI and we know that it has an illegal type, see if
|
|
// it is only used by trunc or trunc(lshr) operations. If so, we split the
|
|
// PHI into the various pieces being extracted. This sort of thing is
|
|
// introduced when SROA promotes an aggregate to a single large integer type.
|
|
if (PN.getType()->isIntegerTy() &&
|
|
!DL.isLegalInteger(PN.getType()->getPrimitiveSizeInBits()))
|
|
if (Instruction *Res = SliceUpIllegalIntegerPHI(PN))
|
|
return Res;
|
|
|
|
// Ultimately, try to replace this Phi with a dominating condition.
|
|
if (auto *V = SimplifyUsingControlFlow(*this, PN, DT))
|
|
return replaceInstUsesWith(PN, V);
|
|
|
|
return nullptr;
|
|
}
|