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| //===-- NVPTXPeephole.cpp - NVPTX Peephole Optimiztions -------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// In NVPTX, NVPTXFrameLowering will emit following instruction at the beginning
// of a MachineFunction.
//
// mov %SPL, %depot
// cvta.local %SP, %SPL
//
// Because Frame Index is a generic address and alloca can only return generic
// pointer, without this pass the instructions producing alloca'ed address will
// be based on %SP. NVPTXLowerAlloca tends to help replace store and load on
// this address with their .local versions, but this may introduce a lot of
// cvta.to.local instructions. Performance can be improved if we avoid casting
// address back and forth and directly calculate local address based on %SPL.
// This peephole pass optimizes these cases, for example
//
// It will transform the following pattern
// %0 = LEA_ADDRi64 %VRFrame, 4
// %1 = cvta_to_local_yes_64 %0
//
// into
// %1 = LEA_ADDRi64 %VRFrameLocal, 4
//
// %VRFrameLocal is the virtual register name of %SPL
//
//===----------------------------------------------------------------------===//
#include "NVPTX.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
using namespace llvm;
#define DEBUG_TYPE "nvptx-peephole"
namespace llvm {
void initializeNVPTXPeepholePass(PassRegistry &);
}
namespace {
struct NVPTXPeephole : public MachineFunctionPass {
public:
static char ID;
NVPTXPeephole() : MachineFunctionPass(ID) {
initializeNVPTXPeepholePass(*PassRegistry::getPassRegistry());
}
bool runOnMachineFunction(MachineFunction &MF) override;
StringRef getPassName() const override {
return "NVPTX optimize redundant cvta.to.local instruction";
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
MachineFunctionPass::getAnalysisUsage(AU);
}
};
}
char NVPTXPeephole::ID = 0;
INITIALIZE_PASS(NVPTXPeephole, "nvptx-peephole", "NVPTX Peephole", false, false)
static bool isCVTAToLocalCombinationCandidate(MachineInstr &Root) {
auto &MBB = *Root.getParent();
auto &MF = *MBB.getParent();
// Check current instruction is cvta.to.local
if (Root.getOpcode() != NVPTX::cvta_to_local_yes_64 &&
Root.getOpcode() != NVPTX::cvta_to_local_yes)
return false;
auto &Op = Root.getOperand(1);
const auto &MRI = MF.getRegInfo();
MachineInstr *GenericAddrDef = nullptr;
if (Op.isReg() && Register::isVirtualRegister(Op.getReg())) {
GenericAddrDef = MRI.getUniqueVRegDef(Op.getReg());
}
// Check the register operand is uniquely defined by LEA_ADDRi instruction
if (!GenericAddrDef || GenericAddrDef->getParent() != &MBB ||
(GenericAddrDef->getOpcode() != NVPTX::LEA_ADDRi64 &&
GenericAddrDef->getOpcode() != NVPTX::LEA_ADDRi)) {
return false;
}
// Check the LEA_ADDRi operand is Frame index
auto &BaseAddrOp = GenericAddrDef->getOperand(1);
if (BaseAddrOp.isReg() && BaseAddrOp.getReg() == NVPTX::VRFrame) {
return true;
}
return false;
}
static void CombineCVTAToLocal(MachineInstr &Root) {
auto &MBB = *Root.getParent();
auto &MF = *MBB.getParent();
const auto &MRI = MF.getRegInfo();
const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
auto &Prev = *MRI.getUniqueVRegDef(Root.getOperand(1).getReg());
MachineInstrBuilder MIB =
BuildMI(MF, Root.getDebugLoc(), TII->get(Prev.getOpcode()),
Root.getOperand(0).getReg())
.addReg(NVPTX::VRFrameLocal)
.add(Prev.getOperand(2));
MBB.insert((MachineBasicBlock::iterator)&Root, MIB);
// Check if MRI has only one non dbg use, which is Root
if (MRI.hasOneNonDBGUse(Prev.getOperand(0).getReg())) {
Prev.eraseFromParentAndMarkDBGValuesForRemoval();
}
Root.eraseFromParentAndMarkDBGValuesForRemoval();
}
bool NVPTXPeephole::runOnMachineFunction(MachineFunction &MF) {
if (skipFunction(MF.getFunction()))
return false;
bool Changed = false;
// Loop over all of the basic blocks.
for (auto &MBB : MF) {
// Traverse the basic block.
auto BlockIter = MBB.begin();
while (BlockIter != MBB.end()) {
auto &MI = *BlockIter++;
if (isCVTAToLocalCombinationCandidate(MI)) {
CombineCVTAToLocal(MI);
Changed = true;
}
} // Instruction
} // Basic Block
// Remove unnecessary %VRFrame = cvta.local %VRFrameLocal
const auto &MRI = MF.getRegInfo();
if (MRI.use_empty(NVPTX::VRFrame)) {
if (auto MI = MRI.getUniqueVRegDef(NVPTX::VRFrame)) {
MI->eraseFromParentAndMarkDBGValuesForRemoval();
}
}
return Changed;
}
MachineFunctionPass *llvm::createNVPTXPeephole() { return new NVPTXPeephole(); }
|