979 lines
39 KiB
C++
979 lines
39 KiB
C++
//===-- UnrollLoop.cpp - Loop unrolling utilities -------------------------===//
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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 some loop unrolling utilities. It does not define any
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// actual pass or policy, but provides a single function to perform loop
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// unrolling.
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//
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// The process of unrolling can produce extraneous basic blocks linked with
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// unconditional branches. This will be corrected in the future.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/ADT/ArrayRef.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/Optional.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ADT/SetVector.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/StringRef.h"
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#include "llvm/ADT/Twine.h"
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#include "llvm/ADT/ilist_iterator.h"
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#include "llvm/ADT/iterator_range.h"
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#include "llvm/Analysis/AssumptionCache.h"
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#include "llvm/Analysis/DomTreeUpdater.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/LoopIterator.h"
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#include "llvm/Analysis/OptimizationRemarkEmitter.h"
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#include "llvm/Analysis/ScalarEvolution.h"
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/IR/CFG.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DebugInfoMetadata.h"
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#include "llvm/IR/DebugLoc.h"
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#include "llvm/IR/DiagnosticInfo.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/Instruction.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/Metadata.h"
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#include "llvm/IR/Module.h"
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#include "llvm/IR/Use.h"
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#include "llvm/IR/User.h"
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#include "llvm/IR/ValueHandle.h"
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#include "llvm/IR/ValueMap.h"
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#include "llvm/Support/Casting.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/GenericDomTree.h"
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#include "llvm/Support/MathExtras.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Transforms/Utils/Cloning.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Transforms/Utils/LoopPeel.h"
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#include "llvm/Transforms/Utils/LoopSimplify.h"
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#include "llvm/Transforms/Utils/LoopUtils.h"
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#include "llvm/Transforms/Utils/SimplifyIndVar.h"
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#include "llvm/Transforms/Utils/UnrollLoop.h"
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#include "llvm/Transforms/Utils/ValueMapper.h"
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#include <algorithm>
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#include <assert.h>
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#include <type_traits>
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#include <vector>
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namespace llvm {
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class DataLayout;
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class Value;
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} // namespace llvm
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using namespace llvm;
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#define DEBUG_TYPE "loop-unroll"
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// TODO: Should these be here or in LoopUnroll?
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STATISTIC(NumCompletelyUnrolled, "Number of loops completely unrolled");
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STATISTIC(NumUnrolled, "Number of loops unrolled (completely or otherwise)");
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STATISTIC(NumUnrolledNotLatch, "Number of loops unrolled without a conditional "
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"latch (completely or otherwise)");
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static cl::opt<bool>
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UnrollRuntimeEpilog("unroll-runtime-epilog", cl::init(false), cl::Hidden,
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cl::desc("Allow runtime unrolled loops to be unrolled "
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"with epilog instead of prolog."));
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static cl::opt<bool>
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UnrollVerifyDomtree("unroll-verify-domtree", cl::Hidden,
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cl::desc("Verify domtree after unrolling"),
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#ifdef EXPENSIVE_CHECKS
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cl::init(true)
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#else
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cl::init(false)
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#endif
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);
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/// Check if unrolling created a situation where we need to insert phi nodes to
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/// preserve LCSSA form.
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/// \param Blocks is a vector of basic blocks representing unrolled loop.
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/// \param L is the outer loop.
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/// It's possible that some of the blocks are in L, and some are not. In this
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/// case, if there is a use is outside L, and definition is inside L, we need to
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/// insert a phi-node, otherwise LCSSA will be broken.
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/// The function is just a helper function for llvm::UnrollLoop that returns
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/// true if this situation occurs, indicating that LCSSA needs to be fixed.
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static bool needToInsertPhisForLCSSA(Loop *L,
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const std::vector<BasicBlock *> &Blocks,
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LoopInfo *LI) {
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for (BasicBlock *BB : Blocks) {
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if (LI->getLoopFor(BB) == L)
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continue;
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for (Instruction &I : *BB) {
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for (Use &U : I.operands()) {
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if (const auto *Def = dyn_cast<Instruction>(U)) {
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Loop *DefLoop = LI->getLoopFor(Def->getParent());
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if (!DefLoop)
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continue;
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if (DefLoop->contains(L))
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return true;
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}
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}
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}
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}
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return false;
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}
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/// Adds ClonedBB to LoopInfo, creates a new loop for ClonedBB if necessary
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/// and adds a mapping from the original loop to the new loop to NewLoops.
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/// Returns nullptr if no new loop was created and a pointer to the
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/// original loop OriginalBB was part of otherwise.
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const Loop* llvm::addClonedBlockToLoopInfo(BasicBlock *OriginalBB,
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BasicBlock *ClonedBB, LoopInfo *LI,
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NewLoopsMap &NewLoops) {
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// Figure out which loop New is in.
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const Loop *OldLoop = LI->getLoopFor(OriginalBB);
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assert(OldLoop && "Should (at least) be in the loop being unrolled!");
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Loop *&NewLoop = NewLoops[OldLoop];
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if (!NewLoop) {
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// Found a new sub-loop.
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assert(OriginalBB == OldLoop->getHeader() &&
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"Header should be first in RPO");
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NewLoop = LI->AllocateLoop();
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Loop *NewLoopParent = NewLoops.lookup(OldLoop->getParentLoop());
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if (NewLoopParent)
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NewLoopParent->addChildLoop(NewLoop);
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else
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LI->addTopLevelLoop(NewLoop);
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NewLoop->addBasicBlockToLoop(ClonedBB, *LI);
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return OldLoop;
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} else {
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NewLoop->addBasicBlockToLoop(ClonedBB, *LI);
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return nullptr;
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}
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}
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/// The function chooses which type of unroll (epilog or prolog) is more
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/// profitabale.
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/// Epilog unroll is more profitable when there is PHI that starts from
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/// constant. In this case epilog will leave PHI start from constant,
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/// but prolog will convert it to non-constant.
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///
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/// loop:
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/// PN = PHI [I, Latch], [CI, PreHeader]
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/// I = foo(PN)
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/// ...
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///
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/// Epilog unroll case.
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/// loop:
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/// PN = PHI [I2, Latch], [CI, PreHeader]
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/// I1 = foo(PN)
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/// I2 = foo(I1)
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/// ...
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/// Prolog unroll case.
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/// NewPN = PHI [PrologI, Prolog], [CI, PreHeader]
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/// loop:
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/// PN = PHI [I2, Latch], [NewPN, PreHeader]
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/// I1 = foo(PN)
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/// I2 = foo(I1)
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/// ...
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///
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static bool isEpilogProfitable(Loop *L) {
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BasicBlock *PreHeader = L->getLoopPreheader();
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BasicBlock *Header = L->getHeader();
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assert(PreHeader && Header);
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for (const PHINode &PN : Header->phis()) {
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if (isa<ConstantInt>(PN.getIncomingValueForBlock(PreHeader)))
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return true;
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}
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return false;
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}
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/// Perform some cleanup and simplifications on loops after unrolling. It is
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/// useful to simplify the IV's in the new loop, as well as do a quick
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/// simplify/dce pass of the instructions.
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void llvm::simplifyLoopAfterUnroll(Loop *L, bool SimplifyIVs, LoopInfo *LI,
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ScalarEvolution *SE, DominatorTree *DT,
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AssumptionCache *AC,
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const TargetTransformInfo *TTI) {
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// Simplify any new induction variables in the partially unrolled loop.
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if (SE && SimplifyIVs) {
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SmallVector<WeakTrackingVH, 16> DeadInsts;
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simplifyLoopIVs(L, SE, DT, LI, TTI, DeadInsts);
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// Aggressively clean up dead instructions that simplifyLoopIVs already
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// identified. Any remaining should be cleaned up below.
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while (!DeadInsts.empty()) {
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Value *V = DeadInsts.pop_back_val();
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if (Instruction *Inst = dyn_cast_or_null<Instruction>(V))
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RecursivelyDeleteTriviallyDeadInstructions(Inst);
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}
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}
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// At this point, the code is well formed. We now do a quick sweep over the
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// inserted code, doing constant propagation and dead code elimination as we
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// go.
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const DataLayout &DL = L->getHeader()->getModule()->getDataLayout();
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for (BasicBlock *BB : L->getBlocks()) {
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for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;) {
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Instruction *Inst = &*I++;
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if (Value *V = SimplifyInstruction(Inst, {DL, nullptr, DT, AC}))
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if (LI->replacementPreservesLCSSAForm(Inst, V))
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Inst->replaceAllUsesWith(V);
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if (isInstructionTriviallyDead(Inst))
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BB->getInstList().erase(Inst);
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}
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}
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// TODO: after peeling or unrolling, previously loop variant conditions are
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// likely to fold to constants, eagerly propagating those here will require
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// fewer cleanup passes to be run. Alternatively, a LoopEarlyCSE might be
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// appropriate.
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}
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/// Unroll the given loop by Count. The loop must be in LCSSA form. Unrolling
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/// can only fail when the loop's latch block is not terminated by a conditional
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/// branch instruction. However, if the trip count (and multiple) are not known,
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/// loop unrolling will mostly produce more code that is no faster.
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///
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/// TripCount is the upper bound of the iteration on which control exits
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/// LatchBlock. Control may exit the loop prior to TripCount iterations either
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/// via an early branch in other loop block or via LatchBlock terminator. This
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/// is relaxed from the general definition of trip count which is the number of
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/// times the loop header executes. Note that UnrollLoop assumes that the loop
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/// counter test is in LatchBlock in order to remove unnecesssary instances of
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/// the test. If control can exit the loop from the LatchBlock's terminator
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/// prior to TripCount iterations, flag PreserveCondBr needs to be set.
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///
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/// PreserveCondBr indicates whether the conditional branch of the LatchBlock
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/// needs to be preserved. It is needed when we use trip count upper bound to
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/// fully unroll the loop. If PreserveOnlyFirst is also set then only the first
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/// conditional branch needs to be preserved.
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///
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/// Similarly, TripMultiple divides the number of times that the LatchBlock may
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/// execute without exiting the loop.
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///
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/// If AllowRuntime is true then UnrollLoop will consider unrolling loops that
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/// have a runtime (i.e. not compile time constant) trip count. Unrolling these
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/// loops require a unroll "prologue" that runs "RuntimeTripCount % Count"
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/// iterations before branching into the unrolled loop. UnrollLoop will not
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/// runtime-unroll the loop if computing RuntimeTripCount will be expensive and
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/// AllowExpensiveTripCount is false.
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///
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/// If we want to perform PGO-based loop peeling, PeelCount is set to the
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/// number of iterations we want to peel off.
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///
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/// The LoopInfo Analysis that is passed will be kept consistent.
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///
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/// This utility preserves LoopInfo. It will also preserve ScalarEvolution and
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/// DominatorTree if they are non-null.
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///
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/// If RemainderLoop is non-null, it will receive the remainder loop (if
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/// required and not fully unrolled).
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LoopUnrollResult llvm::UnrollLoop(Loop *L, UnrollLoopOptions ULO, LoopInfo *LI,
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ScalarEvolution *SE, DominatorTree *DT,
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AssumptionCache *AC,
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const TargetTransformInfo *TTI,
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OptimizationRemarkEmitter *ORE,
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bool PreserveLCSSA, Loop **RemainderLoop) {
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if (!L->getLoopPreheader()) {
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LLVM_DEBUG(dbgs() << " Can't unroll; loop preheader-insertion failed.\n");
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return LoopUnrollResult::Unmodified;
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}
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if (!L->getLoopLatch()) {
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LLVM_DEBUG(dbgs() << " Can't unroll; loop exit-block-insertion failed.\n");
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return LoopUnrollResult::Unmodified;
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}
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// Loops with indirectbr cannot be cloned.
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if (!L->isSafeToClone()) {
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LLVM_DEBUG(dbgs() << " Can't unroll; Loop body cannot be cloned.\n");
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return LoopUnrollResult::Unmodified;
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}
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if (L->getHeader()->hasAddressTaken()) {
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// The loop-rotate pass can be helpful to avoid this in many cases.
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LLVM_DEBUG(
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dbgs() << " Won't unroll loop: address of header block is taken.\n");
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return LoopUnrollResult::Unmodified;
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}
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if (ULO.TripCount != 0)
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LLVM_DEBUG(dbgs() << " Trip Count = " << ULO.TripCount << "\n");
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if (ULO.TripMultiple != 1)
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LLVM_DEBUG(dbgs() << " Trip Multiple = " << ULO.TripMultiple << "\n");
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// Effectively "DCE" unrolled iterations that are beyond the tripcount
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// and will never be executed.
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if (ULO.TripCount != 0 && ULO.Count > ULO.TripCount)
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ULO.Count = ULO.TripCount;
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// Don't enter the unroll code if there is nothing to do.
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if (ULO.TripCount == 0 && ULO.Count < 2 && ULO.PeelCount == 0) {
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LLVM_DEBUG(dbgs() << "Won't unroll; almost nothing to do\n");
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return LoopUnrollResult::Unmodified;
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}
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assert(ULO.Count > 0);
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assert(ULO.TripMultiple > 0);
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assert(ULO.TripCount == 0 || ULO.TripCount % ULO.TripMultiple == 0);
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// Are we eliminating the loop control altogether?
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bool CompletelyUnroll = ULO.Count == ULO.TripCount;
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// We assume a run-time trip count if the compiler cannot
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// figure out the loop trip count and the unroll-runtime
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// flag is specified.
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bool RuntimeTripCount =
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(ULO.TripCount == 0 && ULO.Count > 0 && ULO.AllowRuntime);
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assert((!RuntimeTripCount || !ULO.PeelCount) &&
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"Did not expect runtime trip-count unrolling "
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"and peeling for the same loop");
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bool Peeled = false;
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if (ULO.PeelCount) {
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Peeled = peelLoop(L, ULO.PeelCount, LI, SE, DT, AC, PreserveLCSSA);
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// Successful peeling may result in a change in the loop preheader/trip
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// counts. If we later unroll the loop, we want these to be updated.
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if (Peeled) {
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// According to our guards and profitability checks the only
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// meaningful exit should be latch block. Other exits go to deopt,
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// so we do not worry about them.
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BasicBlock *ExitingBlock = L->getLoopLatch();
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assert(ExitingBlock && "Loop without exiting block?");
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assert(L->isLoopExiting(ExitingBlock) && "Latch is not exiting?");
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ULO.TripCount = SE->getSmallConstantTripCount(L, ExitingBlock);
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ULO.TripMultiple = SE->getSmallConstantTripMultiple(L, ExitingBlock);
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}
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}
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// All these values should be taken only after peeling because they might have
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// changed.
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BasicBlock *Preheader = L->getLoopPreheader();
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BasicBlock *Header = L->getHeader();
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BasicBlock *LatchBlock = L->getLoopLatch();
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SmallVector<BasicBlock *, 4> ExitBlocks;
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L->getExitBlocks(ExitBlocks);
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std::vector<BasicBlock *> OriginalLoopBlocks = L->getBlocks();
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// Go through all exits of L and see if there are any phi-nodes there. We just
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// conservatively assume that they're inserted to preserve LCSSA form, which
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// means that complete unrolling might break this form. We need to either fix
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// it in-place after the transformation, or entirely rebuild LCSSA. TODO: For
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// now we just recompute LCSSA for the outer loop, but it should be possible
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// to fix it in-place.
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bool NeedToFixLCSSA =
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PreserveLCSSA && CompletelyUnroll &&
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any_of(ExitBlocks,
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[](const BasicBlock *BB) { return isa<PHINode>(BB->begin()); });
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// The current loop unroll pass can unroll loops that have
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// (1) single latch; and
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// (2a) latch is unconditional; or
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// (2b) latch is conditional and is an exiting block
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// FIXME: The implementation can be extended to work with more complicated
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// cases, e.g. loops with multiple latches.
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BranchInst *LatchBI = dyn_cast<BranchInst>(LatchBlock->getTerminator());
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// A conditional branch which exits the loop, which can be optimized to an
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// unconditional branch in the unrolled loop in some cases.
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BranchInst *ExitingBI = nullptr;
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bool LatchIsExiting = L->isLoopExiting(LatchBlock);
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if (LatchIsExiting)
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ExitingBI = LatchBI;
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else if (BasicBlock *ExitingBlock = L->getExitingBlock())
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ExitingBI = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
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if (!LatchBI || (LatchBI->isConditional() && !LatchIsExiting)) {
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// If the peeling guard is changed this assert may be relaxed or even
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// deleted.
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assert(!Peeled && "Peeling guard changed!");
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LLVM_DEBUG(
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dbgs() << "Can't unroll; a conditional latch must exit the loop");
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return LoopUnrollResult::Unmodified;
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}
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LLVM_DEBUG({
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if (ExitingBI)
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dbgs() << " Exiting Block = " << ExitingBI->getParent()->getName()
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<< "\n";
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else
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dbgs() << " No single exiting block\n";
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});
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// Loops containing convergent instructions must have a count that divides
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// their TripMultiple.
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LLVM_DEBUG(
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{
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bool HasConvergent = false;
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for (auto &BB : L->blocks())
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for (auto &I : *BB)
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if (auto *CB = dyn_cast<CallBase>(&I))
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HasConvergent |= CB->isConvergent();
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assert((!HasConvergent || ULO.TripMultiple % ULO.Count == 0) &&
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"Unroll count must divide trip multiple if loop contains a "
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"convergent operation.");
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});
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bool EpilogProfitability =
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UnrollRuntimeEpilog.getNumOccurrences() ? UnrollRuntimeEpilog
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: isEpilogProfitable(L);
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if (RuntimeTripCount && ULO.TripMultiple % ULO.Count != 0 &&
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!UnrollRuntimeLoopRemainder(L, ULO.Count, ULO.AllowExpensiveTripCount,
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EpilogProfitability, ULO.UnrollRemainder,
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ULO.ForgetAllSCEV, LI, SE, DT, AC, TTI,
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PreserveLCSSA, RemainderLoop)) {
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if (ULO.Force)
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RuntimeTripCount = false;
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else {
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LLVM_DEBUG(dbgs() << "Won't unroll; remainder loop could not be "
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"generated when assuming runtime trip count\n");
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return LoopUnrollResult::Unmodified;
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}
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}
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|
|
|
// If we know the trip count, we know the multiple...
|
|
unsigned BreakoutTrip = 0;
|
|
if (ULO.TripCount != 0) {
|
|
BreakoutTrip = ULO.TripCount % ULO.Count;
|
|
ULO.TripMultiple = 0;
|
|
} else {
|
|
// Figure out what multiple to use.
|
|
BreakoutTrip = ULO.TripMultiple =
|
|
(unsigned)GreatestCommonDivisor64(ULO.Count, ULO.TripMultiple);
|
|
}
|
|
|
|
using namespace ore;
|
|
// Report the unrolling decision.
|
|
if (CompletelyUnroll) {
|
|
LLVM_DEBUG(dbgs() << "COMPLETELY UNROLLING loop %" << Header->getName()
|
|
<< " with trip count " << ULO.TripCount << "!\n");
|
|
if (ORE)
|
|
ORE->emit([&]() {
|
|
return OptimizationRemark(DEBUG_TYPE, "FullyUnrolled", L->getStartLoc(),
|
|
L->getHeader())
|
|
<< "completely unrolled loop with "
|
|
<< NV("UnrollCount", ULO.TripCount) << " iterations";
|
|
});
|
|
} else if (ULO.PeelCount) {
|
|
LLVM_DEBUG(dbgs() << "PEELING loop %" << Header->getName()
|
|
<< " with iteration count " << ULO.PeelCount << "!\n");
|
|
if (ORE)
|
|
ORE->emit([&]() {
|
|
return OptimizationRemark(DEBUG_TYPE, "Peeled", L->getStartLoc(),
|
|
L->getHeader())
|
|
<< " peeled loop by " << NV("PeelCount", ULO.PeelCount)
|
|
<< " iterations";
|
|
});
|
|
} else {
|
|
auto DiagBuilder = [&]() {
|
|
OptimizationRemark Diag(DEBUG_TYPE, "PartialUnrolled", L->getStartLoc(),
|
|
L->getHeader());
|
|
return Diag << "unrolled loop by a factor of "
|
|
<< NV("UnrollCount", ULO.Count);
|
|
};
|
|
|
|
LLVM_DEBUG(dbgs() << "UNROLLING loop %" << Header->getName() << " by "
|
|
<< ULO.Count);
|
|
if (ULO.TripMultiple == 0 || BreakoutTrip != ULO.TripMultiple) {
|
|
LLVM_DEBUG(dbgs() << " with a breakout at trip " << BreakoutTrip);
|
|
if (ORE)
|
|
ORE->emit([&]() {
|
|
return DiagBuilder() << " with a breakout at trip "
|
|
<< NV("BreakoutTrip", BreakoutTrip);
|
|
});
|
|
} else if (ULO.TripMultiple != 1) {
|
|
LLVM_DEBUG(dbgs() << " with " << ULO.TripMultiple << " trips per branch");
|
|
if (ORE)
|
|
ORE->emit([&]() {
|
|
return DiagBuilder()
|
|
<< " with " << NV("TripMultiple", ULO.TripMultiple)
|
|
<< " trips per branch";
|
|
});
|
|
} else if (RuntimeTripCount) {
|
|
LLVM_DEBUG(dbgs() << " with run-time trip count");
|
|
if (ORE)
|
|
ORE->emit(
|
|
[&]() { return DiagBuilder() << " with run-time trip count"; });
|
|
}
|
|
LLVM_DEBUG(dbgs() << "!\n");
|
|
}
|
|
|
|
// We are going to make changes to this loop. SCEV may be keeping cached info
|
|
// about it, in particular about backedge taken count. The changes we make
|
|
// are guaranteed to invalidate this information for our loop. It is tempting
|
|
// to only invalidate the loop being unrolled, but it is incorrect as long as
|
|
// all exiting branches from all inner loops have impact on the outer loops,
|
|
// and if something changes inside them then any of outer loops may also
|
|
// change. When we forget outermost loop, we also forget all contained loops
|
|
// and this is what we need here.
|
|
if (SE) {
|
|
if (ULO.ForgetAllSCEV)
|
|
SE->forgetAllLoops();
|
|
else
|
|
SE->forgetTopmostLoop(L);
|
|
}
|
|
|
|
if (!LatchIsExiting)
|
|
++NumUnrolledNotLatch;
|
|
Optional<bool> ContinueOnTrue = None;
|
|
BasicBlock *LoopExit = nullptr;
|
|
if (ExitingBI) {
|
|
ContinueOnTrue = L->contains(ExitingBI->getSuccessor(0));
|
|
LoopExit = ExitingBI->getSuccessor(*ContinueOnTrue);
|
|
}
|
|
|
|
// For the first iteration of the loop, we should use the precloned values for
|
|
// PHI nodes. Insert associations now.
|
|
ValueToValueMapTy LastValueMap;
|
|
std::vector<PHINode*> OrigPHINode;
|
|
for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
|
|
OrigPHINode.push_back(cast<PHINode>(I));
|
|
}
|
|
|
|
std::vector<BasicBlock *> Headers;
|
|
std::vector<BasicBlock *> ExitingBlocks;
|
|
std::vector<BasicBlock *> ExitingSucc;
|
|
std::vector<BasicBlock *> Latches;
|
|
Headers.push_back(Header);
|
|
Latches.push_back(LatchBlock);
|
|
if (ExitingBI) {
|
|
ExitingBlocks.push_back(ExitingBI->getParent());
|
|
ExitingSucc.push_back(ExitingBI->getSuccessor(!(*ContinueOnTrue)));
|
|
}
|
|
|
|
// The current on-the-fly SSA update requires blocks to be processed in
|
|
// reverse postorder so that LastValueMap contains the correct value at each
|
|
// exit.
|
|
LoopBlocksDFS DFS(L);
|
|
DFS.perform(LI);
|
|
|
|
// Stash the DFS iterators before adding blocks to the loop.
|
|
LoopBlocksDFS::RPOIterator BlockBegin = DFS.beginRPO();
|
|
LoopBlocksDFS::RPOIterator BlockEnd = DFS.endRPO();
|
|
|
|
std::vector<BasicBlock*> UnrolledLoopBlocks = L->getBlocks();
|
|
|
|
// Loop Unrolling might create new loops. While we do preserve LoopInfo, we
|
|
// might break loop-simplified form for these loops (as they, e.g., would
|
|
// share the same exit blocks). We'll keep track of loops for which we can
|
|
// break this so that later we can re-simplify them.
|
|
SmallSetVector<Loop *, 4> LoopsToSimplify;
|
|
for (Loop *SubLoop : *L)
|
|
LoopsToSimplify.insert(SubLoop);
|
|
|
|
if (Header->getParent()->isDebugInfoForProfiling())
|
|
for (BasicBlock *BB : L->getBlocks())
|
|
for (Instruction &I : *BB)
|
|
if (!isa<DbgInfoIntrinsic>(&I))
|
|
if (const DILocation *DIL = I.getDebugLoc()) {
|
|
auto NewDIL = DIL->cloneByMultiplyingDuplicationFactor(ULO.Count);
|
|
if (NewDIL)
|
|
I.setDebugLoc(NewDIL.getValue());
|
|
else
|
|
LLVM_DEBUG(dbgs()
|
|
<< "Failed to create new discriminator: "
|
|
<< DIL->getFilename() << " Line: " << DIL->getLine());
|
|
}
|
|
|
|
// Identify what noalias metadata is inside the loop: if it is inside the
|
|
// loop, the associated metadata must be cloned for each iteration.
|
|
SmallVector<MDNode *, 6> LoopLocalNoAliasDeclScopes;
|
|
identifyNoAliasScopesToClone(L->getBlocks(), LoopLocalNoAliasDeclScopes);
|
|
|
|
for (unsigned It = 1; It != ULO.Count; ++It) {
|
|
SmallVector<BasicBlock *, 8> NewBlocks;
|
|
SmallDenseMap<const Loop *, Loop *, 4> NewLoops;
|
|
NewLoops[L] = L;
|
|
|
|
for (LoopBlocksDFS::RPOIterator BB = BlockBegin; BB != BlockEnd; ++BB) {
|
|
ValueToValueMapTy VMap;
|
|
BasicBlock *New = CloneBasicBlock(*BB, VMap, "." + Twine(It));
|
|
Header->getParent()->getBasicBlockList().push_back(New);
|
|
|
|
assert((*BB != Header || LI->getLoopFor(*BB) == L) &&
|
|
"Header should not be in a sub-loop");
|
|
// Tell LI about New.
|
|
const Loop *OldLoop = addClonedBlockToLoopInfo(*BB, New, LI, NewLoops);
|
|
if (OldLoop)
|
|
LoopsToSimplify.insert(NewLoops[OldLoop]);
|
|
|
|
if (*BB == Header)
|
|
// Loop over all of the PHI nodes in the block, changing them to use
|
|
// the incoming values from the previous block.
|
|
for (PHINode *OrigPHI : OrigPHINode) {
|
|
PHINode *NewPHI = cast<PHINode>(VMap[OrigPHI]);
|
|
Value *InVal = NewPHI->getIncomingValueForBlock(LatchBlock);
|
|
if (Instruction *InValI = dyn_cast<Instruction>(InVal))
|
|
if (It > 1 && L->contains(InValI))
|
|
InVal = LastValueMap[InValI];
|
|
VMap[OrigPHI] = InVal;
|
|
New->getInstList().erase(NewPHI);
|
|
}
|
|
|
|
// Update our running map of newest clones
|
|
LastValueMap[*BB] = New;
|
|
for (ValueToValueMapTy::iterator VI = VMap.begin(), VE = VMap.end();
|
|
VI != VE; ++VI)
|
|
LastValueMap[VI->first] = VI->second;
|
|
|
|
// Add phi entries for newly created values to all exit blocks.
|
|
for (BasicBlock *Succ : successors(*BB)) {
|
|
if (L->contains(Succ))
|
|
continue;
|
|
for (PHINode &PHI : Succ->phis()) {
|
|
Value *Incoming = PHI.getIncomingValueForBlock(*BB);
|
|
ValueToValueMapTy::iterator It = LastValueMap.find(Incoming);
|
|
if (It != LastValueMap.end())
|
|
Incoming = It->second;
|
|
PHI.addIncoming(Incoming, New);
|
|
}
|
|
}
|
|
// Keep track of new headers and latches as we create them, so that
|
|
// we can insert the proper branches later.
|
|
if (*BB == Header)
|
|
Headers.push_back(New);
|
|
if (*BB == LatchBlock)
|
|
Latches.push_back(New);
|
|
|
|
// Keep track of the exiting block and its successor block contained in
|
|
// the loop for the current iteration.
|
|
if (ExitingBI) {
|
|
if (*BB == ExitingBlocks[0])
|
|
ExitingBlocks.push_back(New);
|
|
if (*BB == ExitingSucc[0])
|
|
ExitingSucc.push_back(New);
|
|
}
|
|
|
|
NewBlocks.push_back(New);
|
|
UnrolledLoopBlocks.push_back(New);
|
|
|
|
// Update DomTree: since we just copy the loop body, and each copy has a
|
|
// dedicated entry block (copy of the header block), this header's copy
|
|
// dominates all copied blocks. That means, dominance relations in the
|
|
// copied body are the same as in the original body.
|
|
if (DT) {
|
|
if (*BB == Header)
|
|
DT->addNewBlock(New, Latches[It - 1]);
|
|
else {
|
|
auto BBDomNode = DT->getNode(*BB);
|
|
auto BBIDom = BBDomNode->getIDom();
|
|
BasicBlock *OriginalBBIDom = BBIDom->getBlock();
|
|
DT->addNewBlock(
|
|
New, cast<BasicBlock>(LastValueMap[cast<Value>(OriginalBBIDom)]));
|
|
}
|
|
}
|
|
}
|
|
|
|
// Remap all instructions in the most recent iteration
|
|
remapInstructionsInBlocks(NewBlocks, LastValueMap);
|
|
for (BasicBlock *NewBlock : NewBlocks) {
|
|
for (Instruction &I : *NewBlock) {
|
|
if (auto *II = dyn_cast<IntrinsicInst>(&I))
|
|
if (II->getIntrinsicID() == Intrinsic::assume)
|
|
AC->registerAssumption(II);
|
|
}
|
|
}
|
|
|
|
{
|
|
// Identify what other metadata depends on the cloned version. After
|
|
// cloning, replace the metadata with the corrected version for both
|
|
// memory instructions and noalias intrinsics.
|
|
std::string ext = (Twine("It") + Twine(It)).str();
|
|
cloneAndAdaptNoAliasScopes(LoopLocalNoAliasDeclScopes, NewBlocks,
|
|
Header->getContext(), ext);
|
|
}
|
|
}
|
|
|
|
// Loop over the PHI nodes in the original block, setting incoming values.
|
|
for (PHINode *PN : OrigPHINode) {
|
|
if (CompletelyUnroll) {
|
|
PN->replaceAllUsesWith(PN->getIncomingValueForBlock(Preheader));
|
|
Header->getInstList().erase(PN);
|
|
} else if (ULO.Count > 1) {
|
|
Value *InVal = PN->removeIncomingValue(LatchBlock, false);
|
|
// If this value was defined in the loop, take the value defined by the
|
|
// last iteration of the loop.
|
|
if (Instruction *InValI = dyn_cast<Instruction>(InVal)) {
|
|
if (L->contains(InValI))
|
|
InVal = LastValueMap[InVal];
|
|
}
|
|
assert(Latches.back() == LastValueMap[LatchBlock] && "bad last latch");
|
|
PN->addIncoming(InVal, Latches.back());
|
|
}
|
|
}
|
|
|
|
auto setDest = [](BasicBlock *Src, BasicBlock *Dest, BasicBlock *BlockInLoop,
|
|
bool NeedConditional, Optional<bool> ContinueOnTrue,
|
|
bool IsDestLoopExit) {
|
|
auto *Term = cast<BranchInst>(Src->getTerminator());
|
|
if (NeedConditional) {
|
|
// Update the conditional branch's successor for the following
|
|
// iteration.
|
|
assert(ContinueOnTrue.hasValue() &&
|
|
"Expecting valid ContinueOnTrue when NeedConditional is true");
|
|
Term->setSuccessor(!(*ContinueOnTrue), Dest);
|
|
} else {
|
|
// Remove phi operands at this loop exit
|
|
if (!IsDestLoopExit) {
|
|
BasicBlock *BB = Src;
|
|
for (BasicBlock *Succ : successors(BB)) {
|
|
// Preserve the incoming value from BB if we are jumping to the block
|
|
// in the current loop.
|
|
if (Succ == BlockInLoop)
|
|
continue;
|
|
for (PHINode &Phi : Succ->phis())
|
|
Phi.removeIncomingValue(BB, false);
|
|
}
|
|
}
|
|
// Replace the conditional branch with an unconditional one.
|
|
BranchInst::Create(Dest, Term);
|
|
Term->eraseFromParent();
|
|
}
|
|
};
|
|
|
|
// Connect latches of the unrolled iterations to the headers of the next
|
|
// iteration. If the latch is also the exiting block, the conditional branch
|
|
// may have to be preserved.
|
|
for (unsigned i = 0, e = Latches.size(); i != e; ++i) {
|
|
// The branch destination.
|
|
unsigned j = (i + 1) % e;
|
|
BasicBlock *Dest = Headers[j];
|
|
bool NeedConditional = LatchIsExiting;
|
|
|
|
if (LatchIsExiting) {
|
|
if (RuntimeTripCount && j != 0)
|
|
NeedConditional = false;
|
|
|
|
// For a complete unroll, make the last iteration end with a branch
|
|
// to the exit block.
|
|
if (CompletelyUnroll) {
|
|
if (j == 0)
|
|
Dest = LoopExit;
|
|
// If using trip count upper bound to completely unroll, we need to
|
|
// keep the conditional branch except the last one because the loop
|
|
// may exit after any iteration.
|
|
assert(NeedConditional &&
|
|
"NeedCondition cannot be modified by both complete "
|
|
"unrolling and runtime unrolling");
|
|
NeedConditional =
|
|
(ULO.PreserveCondBr && j && !(ULO.PreserveOnlyFirst && i != 0));
|
|
} else if (j != BreakoutTrip &&
|
|
(ULO.TripMultiple == 0 || j % ULO.TripMultiple != 0)) {
|
|
// If we know the trip count or a multiple of it, we can safely use an
|
|
// unconditional branch for some iterations.
|
|
NeedConditional = false;
|
|
}
|
|
}
|
|
|
|
setDest(Latches[i], Dest, Headers[i], NeedConditional, ContinueOnTrue,
|
|
Dest == LoopExit);
|
|
}
|
|
|
|
if (!LatchIsExiting) {
|
|
// If the latch is not exiting, we may be able to simplify the conditional
|
|
// branches in the unrolled exiting blocks.
|
|
for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) {
|
|
// The branch destination.
|
|
unsigned j = (i + 1) % e;
|
|
bool NeedConditional = true;
|
|
|
|
if (RuntimeTripCount && j != 0)
|
|
NeedConditional = false;
|
|
|
|
if (CompletelyUnroll)
|
|
// We cannot drop the conditional branch for the last condition, as we
|
|
// may have to execute the loop body depending on the condition.
|
|
NeedConditional = j == 0 || ULO.PreserveCondBr;
|
|
else if (j != BreakoutTrip &&
|
|
(ULO.TripMultiple == 0 || j % ULO.TripMultiple != 0))
|
|
// If we know the trip count or a multiple of it, we can safely use an
|
|
// unconditional branch for some iterations.
|
|
NeedConditional = false;
|
|
|
|
// Conditional branches from non-latch exiting block have successors
|
|
// either in the same loop iteration or outside the loop. The branches are
|
|
// already correct.
|
|
if (NeedConditional)
|
|
continue;
|
|
setDest(ExitingBlocks[i], ExitingSucc[i], ExitingSucc[i], NeedConditional,
|
|
None, false);
|
|
}
|
|
|
|
// When completely unrolling, the last latch becomes unreachable.
|
|
if (CompletelyUnroll) {
|
|
BranchInst *Term = cast<BranchInst>(Latches.back()->getTerminator());
|
|
new UnreachableInst(Term->getContext(), Term);
|
|
Term->eraseFromParent();
|
|
}
|
|
}
|
|
|
|
// Update dominators of blocks we might reach through exits.
|
|
// Immediate dominator of such block might change, because we add more
|
|
// routes which can lead to the exit: we can now reach it from the copied
|
|
// iterations too.
|
|
if (DT && ULO.Count > 1) {
|
|
for (auto *BB : OriginalLoopBlocks) {
|
|
auto *BBDomNode = DT->getNode(BB);
|
|
SmallVector<BasicBlock *, 16> ChildrenToUpdate;
|
|
for (auto *ChildDomNode : BBDomNode->children()) {
|
|
auto *ChildBB = ChildDomNode->getBlock();
|
|
if (!L->contains(ChildBB))
|
|
ChildrenToUpdate.push_back(ChildBB);
|
|
}
|
|
BasicBlock *NewIDom;
|
|
if (ExitingBI && BB == ExitingBlocks[0]) {
|
|
// The latch is special because we emit unconditional branches in
|
|
// some cases where the original loop contained a conditional branch.
|
|
// Since the latch is always at the bottom of the loop, if the latch
|
|
// dominated an exit before unrolling, the new dominator of that exit
|
|
// must also be a latch. Specifically, the dominator is the first
|
|
// latch which ends in a conditional branch, or the last latch if
|
|
// there is no such latch.
|
|
// For loops exiting from non latch exiting block, we limit the
|
|
// branch simplification to single exiting block loops.
|
|
NewIDom = ExitingBlocks.back();
|
|
for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) {
|
|
Instruction *Term = ExitingBlocks[i]->getTerminator();
|
|
if (isa<BranchInst>(Term) && cast<BranchInst>(Term)->isConditional()) {
|
|
NewIDom =
|
|
DT->findNearestCommonDominator(ExitingBlocks[i], Latches[i]);
|
|
break;
|
|
}
|
|
}
|
|
} else {
|
|
// The new idom of the block will be the nearest common dominator
|
|
// of all copies of the previous idom. This is equivalent to the
|
|
// nearest common dominator of the previous idom and the first latch,
|
|
// which dominates all copies of the previous idom.
|
|
NewIDom = DT->findNearestCommonDominator(BB, LatchBlock);
|
|
}
|
|
for (auto *ChildBB : ChildrenToUpdate)
|
|
DT->changeImmediateDominator(ChildBB, NewIDom);
|
|
}
|
|
}
|
|
|
|
assert(!DT || !UnrollVerifyDomtree ||
|
|
DT->verify(DominatorTree::VerificationLevel::Fast));
|
|
|
|
DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
|
|
// Merge adjacent basic blocks, if possible.
|
|
for (BasicBlock *Latch : Latches) {
|
|
BranchInst *Term = dyn_cast<BranchInst>(Latch->getTerminator());
|
|
assert((Term ||
|
|
(CompletelyUnroll && !LatchIsExiting && Latch == Latches.back())) &&
|
|
"Need a branch as terminator, except when fully unrolling with "
|
|
"unconditional latch");
|
|
if (Term && Term->isUnconditional()) {
|
|
BasicBlock *Dest = Term->getSuccessor(0);
|
|
BasicBlock *Fold = Dest->getUniquePredecessor();
|
|
if (MergeBlockIntoPredecessor(Dest, &DTU, LI)) {
|
|
// Dest has been folded into Fold. Update our worklists accordingly.
|
|
std::replace(Latches.begin(), Latches.end(), Dest, Fold);
|
|
llvm::erase_value(UnrolledLoopBlocks, Dest);
|
|
}
|
|
}
|
|
}
|
|
// Apply updates to the DomTree.
|
|
DT = &DTU.getDomTree();
|
|
|
|
// At this point, the code is well formed. We now simplify the unrolled loop,
|
|
// doing constant propagation and dead code elimination as we go.
|
|
simplifyLoopAfterUnroll(L, !CompletelyUnroll && (ULO.Count > 1 || Peeled), LI,
|
|
SE, DT, AC, TTI);
|
|
|
|
NumCompletelyUnrolled += CompletelyUnroll;
|
|
++NumUnrolled;
|
|
|
|
Loop *OuterL = L->getParentLoop();
|
|
// Update LoopInfo if the loop is completely removed.
|
|
if (CompletelyUnroll)
|
|
LI->erase(L);
|
|
|
|
// After complete unrolling most of the blocks should be contained in OuterL.
|
|
// However, some of them might happen to be out of OuterL (e.g. if they
|
|
// precede a loop exit). In this case we might need to insert PHI nodes in
|
|
// order to preserve LCSSA form.
|
|
// We don't need to check this if we already know that we need to fix LCSSA
|
|
// form.
|
|
// TODO: For now we just recompute LCSSA for the outer loop in this case, but
|
|
// it should be possible to fix it in-place.
|
|
if (PreserveLCSSA && OuterL && CompletelyUnroll && !NeedToFixLCSSA)
|
|
NeedToFixLCSSA |= ::needToInsertPhisForLCSSA(OuterL, UnrolledLoopBlocks, LI);
|
|
|
|
// If we have a pass and a DominatorTree we should re-simplify impacted loops
|
|
// to ensure subsequent analyses can rely on this form. We want to simplify
|
|
// at least one layer outside of the loop that was unrolled so that any
|
|
// changes to the parent loop exposed by the unrolling are considered.
|
|
if (DT) {
|
|
if (OuterL) {
|
|
// OuterL includes all loops for which we can break loop-simplify, so
|
|
// it's sufficient to simplify only it (it'll recursively simplify inner
|
|
// loops too).
|
|
if (NeedToFixLCSSA) {
|
|
// LCSSA must be performed on the outermost affected loop. The unrolled
|
|
// loop's last loop latch is guaranteed to be in the outermost loop
|
|
// after LoopInfo's been updated by LoopInfo::erase.
|
|
Loop *LatchLoop = LI->getLoopFor(Latches.back());
|
|
Loop *FixLCSSALoop = OuterL;
|
|
if (!FixLCSSALoop->contains(LatchLoop))
|
|
while (FixLCSSALoop->getParentLoop() != LatchLoop)
|
|
FixLCSSALoop = FixLCSSALoop->getParentLoop();
|
|
|
|
formLCSSARecursively(*FixLCSSALoop, *DT, LI, SE);
|
|
} else if (PreserveLCSSA) {
|
|
assert(OuterL->isLCSSAForm(*DT) &&
|
|
"Loops should be in LCSSA form after loop-unroll.");
|
|
}
|
|
|
|
// TODO: That potentially might be compile-time expensive. We should try
|
|
// to fix the loop-simplified form incrementally.
|
|
simplifyLoop(OuterL, DT, LI, SE, AC, nullptr, PreserveLCSSA);
|
|
} else {
|
|
// Simplify loops for which we might've broken loop-simplify form.
|
|
for (Loop *SubLoop : LoopsToSimplify)
|
|
simplifyLoop(SubLoop, DT, LI, SE, AC, nullptr, PreserveLCSSA);
|
|
}
|
|
}
|
|
|
|
return CompletelyUnroll ? LoopUnrollResult::FullyUnrolled
|
|
: LoopUnrollResult::PartiallyUnrolled;
|
|
}
|
|
|
|
/// Given an llvm.loop loop id metadata node, returns the loop hint metadata
|
|
/// node with the given name (for example, "llvm.loop.unroll.count"). If no
|
|
/// such metadata node exists, then nullptr is returned.
|
|
MDNode *llvm::GetUnrollMetadata(MDNode *LoopID, StringRef Name) {
|
|
// First operand should refer to the loop id itself.
|
|
assert(LoopID->getNumOperands() > 0 && "requires at least one operand");
|
|
assert(LoopID->getOperand(0) == LoopID && "invalid loop id");
|
|
|
|
for (unsigned i = 1, e = LoopID->getNumOperands(); i < e; ++i) {
|
|
MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i));
|
|
if (!MD)
|
|
continue;
|
|
|
|
MDString *S = dyn_cast<MDString>(MD->getOperand(0));
|
|
if (!S)
|
|
continue;
|
|
|
|
if (Name.equals(S->getString()))
|
|
return MD;
|
|
}
|
|
return nullptr;
|
|
}
|