327 lines
11 KiB
C++
327 lines
11 KiB
C++
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//===-- MVEVPTBlockPass.cpp - Insert MVE VPT blocks -----------------------===//
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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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#include "ARM.h"
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#include "ARMMachineFunctionInfo.h"
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#include "ARMSubtarget.h"
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#include "MCTargetDesc/ARMBaseInfo.h"
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#include "Thumb2InstrInfo.h"
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#include "llvm/ADT/SmallSet.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/CodeGen/MachineBasicBlock.h"
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#include "llvm/CodeGen/MachineFunction.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineInstr.h"
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#include "llvm/CodeGen/MachineInstrBuilder.h"
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#include "llvm/CodeGen/MachineInstrBundle.h"
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#include "llvm/CodeGen/MachineOperand.h"
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#include "llvm/IR/DebugLoc.h"
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#include "llvm/MC/MCInstrDesc.h"
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#include "llvm/MC/MCRegisterInfo.h"
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#include "llvm/Support/Debug.h"
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#include <cassert>
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#include <new>
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using namespace llvm;
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#define DEBUG_TYPE "arm-mve-vpt"
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namespace {
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class MVEVPTBlock : public MachineFunctionPass {
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public:
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static char ID;
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const Thumb2InstrInfo *TII;
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const TargetRegisterInfo *TRI;
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MVEVPTBlock() : MachineFunctionPass(ID) {}
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bool runOnMachineFunction(MachineFunction &Fn) override;
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MachineFunctionProperties getRequiredProperties() const override {
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return MachineFunctionProperties().set(
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MachineFunctionProperties::Property::NoVRegs);
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}
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StringRef getPassName() const override {
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return "MVE VPT block insertion pass";
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}
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private:
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bool InsertVPTBlocks(MachineBasicBlock &MBB);
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};
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char MVEVPTBlock::ID = 0;
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} // end anonymous namespace
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INITIALIZE_PASS(MVEVPTBlock, DEBUG_TYPE, "ARM MVE VPT block pass", false, false)
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static MachineInstr *findVCMPToFoldIntoVPST(MachineBasicBlock::iterator MI,
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const TargetRegisterInfo *TRI,
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unsigned &NewOpcode) {
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// Search backwards to the instruction that defines VPR. This may or not
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// be a VCMP, we check that after this loop. If we find another instruction
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// that reads cpsr, we return nullptr.
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MachineBasicBlock::iterator CmpMI = MI;
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while (CmpMI != MI->getParent()->begin()) {
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--CmpMI;
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if (CmpMI->modifiesRegister(ARM::VPR, TRI))
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break;
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if (CmpMI->readsRegister(ARM::VPR, TRI))
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break;
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}
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if (CmpMI == MI)
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return nullptr;
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NewOpcode = VCMPOpcodeToVPT(CmpMI->getOpcode());
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if (NewOpcode == 0)
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return nullptr;
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// Search forward from CmpMI to MI, checking if either register was def'd
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if (registerDefinedBetween(CmpMI->getOperand(1).getReg(), std::next(CmpMI),
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MI, TRI))
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return nullptr;
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if (registerDefinedBetween(CmpMI->getOperand(2).getReg(), std::next(CmpMI),
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MI, TRI))
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return nullptr;
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return &*CmpMI;
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}
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// Advances Iter past a block of predicated instructions.
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// Returns true if it successfully skipped the whole block of predicated
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// instructions. Returns false when it stopped early (due to MaxSteps), or if
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// Iter didn't point to a predicated instruction.
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static bool StepOverPredicatedInstrs(MachineBasicBlock::instr_iterator &Iter,
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MachineBasicBlock::instr_iterator EndIter,
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unsigned MaxSteps,
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unsigned &NumInstrsSteppedOver) {
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ARMVCC::VPTCodes NextPred = ARMVCC::None;
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Register PredReg;
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NumInstrsSteppedOver = 0;
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while (Iter != EndIter) {
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NextPred = getVPTInstrPredicate(*Iter, PredReg);
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assert(NextPred != ARMVCC::Else &&
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"VPT block pass does not expect Else preds");
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if (NextPred == ARMVCC::None || MaxSteps == 0)
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break;
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--MaxSteps;
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++Iter;
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++NumInstrsSteppedOver;
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};
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return NumInstrsSteppedOver != 0 &&
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(NextPred == ARMVCC::None || Iter == EndIter);
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}
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// Returns true if at least one instruction in the range [Iter, End) defines
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// or kills VPR.
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static bool IsVPRDefinedOrKilledByBlock(MachineBasicBlock::iterator Iter,
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MachineBasicBlock::iterator End) {
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for (; Iter != End; ++Iter)
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if (Iter->definesRegister(ARM::VPR) || Iter->killsRegister(ARM::VPR))
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return true;
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return false;
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}
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// Creates a T, TT, TTT or TTTT BlockMask depending on BlockSize.
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static ARM::PredBlockMask GetInitialBlockMask(unsigned BlockSize) {
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switch (BlockSize) {
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case 1:
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return ARM::PredBlockMask::T;
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case 2:
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return ARM::PredBlockMask::TT;
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case 3:
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return ARM::PredBlockMask::TTT;
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case 4:
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return ARM::PredBlockMask::TTTT;
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default:
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llvm_unreachable("Invalid BlockSize!");
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}
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}
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// Given an iterator (Iter) that points at an instruction with a "Then"
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// predicate, tries to create the largest block of continuous predicated
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// instructions possible, and returns the VPT Block Mask of that block.
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//
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// This will try to perform some minor optimization in order to maximize the
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// size of the block.
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static ARM::PredBlockMask
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CreateVPTBlock(MachineBasicBlock::instr_iterator &Iter,
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MachineBasicBlock::instr_iterator EndIter,
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SmallVectorImpl<MachineInstr *> &DeadInstructions) {
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MachineBasicBlock::instr_iterator BlockBeg = Iter;
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(void)BlockBeg;
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assert(getVPTInstrPredicate(*Iter) == ARMVCC::Then &&
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"Expected a Predicated Instruction");
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LLVM_DEBUG(dbgs() << "VPT block created for: "; Iter->dump());
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unsigned BlockSize;
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StepOverPredicatedInstrs(Iter, EndIter, 4, BlockSize);
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LLVM_DEBUG(for (MachineBasicBlock::instr_iterator AddedInstIter =
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std::next(BlockBeg);
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AddedInstIter != Iter; ++AddedInstIter) {
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dbgs() << " adding: ";
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AddedInstIter->dump();
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});
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// Generate the initial BlockMask
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ARM::PredBlockMask BlockMask = GetInitialBlockMask(BlockSize);
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// Remove VPNOTs while there's still room in the block, so we can make the
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// largest block possible.
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ARMVCC::VPTCodes CurrentPredicate = ARMVCC::Else;
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while (BlockSize < 4 && Iter != EndIter &&
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Iter->getOpcode() == ARM::MVE_VPNOT) {
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// Try to skip all of the predicated instructions after the VPNOT, stopping
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// after (4 - BlockSize). If we can't skip them all, stop.
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unsigned ElseInstCnt = 0;
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MachineBasicBlock::instr_iterator VPNOTBlockEndIter = std::next(Iter);
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if (!StepOverPredicatedInstrs(VPNOTBlockEndIter, EndIter, (4 - BlockSize),
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ElseInstCnt))
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break;
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// Check if this VPNOT can be removed or not: It can only be removed if at
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// least one of the predicated instruction that follows it kills or sets
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// VPR.
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if (!IsVPRDefinedOrKilledByBlock(Iter, VPNOTBlockEndIter))
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break;
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LLVM_DEBUG(dbgs() << " removing VPNOT: "; Iter->dump(););
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// Record the new size of the block
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BlockSize += ElseInstCnt;
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assert(BlockSize <= 4 && "Block is too large!");
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// Record the VPNot to remove it later.
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DeadInstructions.push_back(&*Iter);
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++Iter;
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// Replace the predicates of the instructions we're adding.
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// Note that we are using "Iter" to iterate over the block so we can update
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// it at the same time.
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for (; Iter != VPNOTBlockEndIter; ++Iter) {
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// Find the register in which the predicate is
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int OpIdx = findFirstVPTPredOperandIdx(*Iter);
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assert(OpIdx != -1);
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// Change the predicate and update the mask
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Iter->getOperand(OpIdx).setImm(CurrentPredicate);
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BlockMask = expandPredBlockMask(BlockMask, CurrentPredicate);
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LLVM_DEBUG(dbgs() << " adding : "; Iter->dump());
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}
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CurrentPredicate =
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(CurrentPredicate == ARMVCC::Then ? ARMVCC::Else : ARMVCC::Then);
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}
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return BlockMask;
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}
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bool MVEVPTBlock::InsertVPTBlocks(MachineBasicBlock &Block) {
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bool Modified = false;
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MachineBasicBlock::instr_iterator MBIter = Block.instr_begin();
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MachineBasicBlock::instr_iterator EndIter = Block.instr_end();
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SmallVector<MachineInstr *, 4> DeadInstructions;
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while (MBIter != EndIter) {
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MachineInstr *MI = &*MBIter;
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Register PredReg;
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DebugLoc DL = MI->getDebugLoc();
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ARMVCC::VPTCodes Pred = getVPTInstrPredicate(*MI, PredReg);
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// The idea of the predicate is that None, Then and Else are for use when
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// handling assembly language: they correspond to the three possible
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// suffixes "", "t" and "e" on the mnemonic. So when instructions are read
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// from assembly source or disassembled from object code, you expect to
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// see a mixture whenever there's a long VPT block. But in code
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// generation, we hope we'll never generate an Else as input to this pass.
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assert(Pred != ARMVCC::Else && "VPT block pass does not expect Else preds");
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if (Pred == ARMVCC::None) {
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++MBIter;
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continue;
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}
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ARM::PredBlockMask BlockMask =
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CreateVPTBlock(MBIter, EndIter, DeadInstructions);
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// Search back for a VCMP that can be folded to create a VPT, or else
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// create a VPST directly
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MachineInstrBuilder MIBuilder;
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unsigned NewOpcode;
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LLVM_DEBUG(dbgs() << " final block mask: " << (unsigned)BlockMask << "\n");
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if (MachineInstr *VCMP = findVCMPToFoldIntoVPST(MI, TRI, NewOpcode)) {
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LLVM_DEBUG(dbgs() << " folding VCMP into VPST: "; VCMP->dump());
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MIBuilder = BuildMI(Block, MI, DL, TII->get(NewOpcode));
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MIBuilder.addImm((uint64_t)BlockMask);
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MIBuilder.add(VCMP->getOperand(1));
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MIBuilder.add(VCMP->getOperand(2));
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MIBuilder.add(VCMP->getOperand(3));
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// We need to remove any kill flags between the original VCMP and the new
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// insertion point.
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for (MachineInstr &MII :
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make_range(VCMP->getIterator(), MI->getIterator())) {
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MII.clearRegisterKills(VCMP->getOperand(1).getReg(), TRI);
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MII.clearRegisterKills(VCMP->getOperand(2).getReg(), TRI);
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}
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VCMP->eraseFromParent();
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} else {
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MIBuilder = BuildMI(Block, MI, DL, TII->get(ARM::MVE_VPST));
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MIBuilder.addImm((uint64_t)BlockMask);
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}
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// Erase all dead instructions (VPNOT's). Do that now so that they do not
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// mess with the bundle creation.
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for (MachineInstr *DeadMI : DeadInstructions)
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DeadMI->eraseFromParent();
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DeadInstructions.clear();
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finalizeBundle(
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Block, MachineBasicBlock::instr_iterator(MIBuilder.getInstr()), MBIter);
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Modified = true;
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}
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return Modified;
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}
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bool MVEVPTBlock::runOnMachineFunction(MachineFunction &Fn) {
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const ARMSubtarget &STI =
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static_cast<const ARMSubtarget &>(Fn.getSubtarget());
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if (!STI.isThumb2() || !STI.hasMVEIntegerOps())
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return false;
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TII = static_cast<const Thumb2InstrInfo *>(STI.getInstrInfo());
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TRI = STI.getRegisterInfo();
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LLVM_DEBUG(dbgs() << "********** ARM MVE VPT BLOCKS **********\n"
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<< "********** Function: " << Fn.getName() << '\n');
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bool Modified = false;
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for (MachineBasicBlock &MBB : Fn)
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Modified |= InsertVPTBlocks(MBB);
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LLVM_DEBUG(dbgs() << "**************************************\n");
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return Modified;
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}
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/// createMVEVPTBlock - Returns an instance of the MVE VPT block
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/// insertion pass.
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FunctionPass *llvm::createMVEVPTBlockPass() { return new MVEVPTBlock(); }
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