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//===-- AMDGPUMarkLastScratchLoad.cpp -------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Mark scratch load/spill instructions which are guaranteed to be the last time
// this scratch slot is used so it can be evicted from caches.
//
// TODO: Handle general stack accesses not just spilling.
//
//===----------------------------------------------------------------------===//
#include "AMDGPU.h"
#include "GCNSubtarget.h"
#include "llvm/CodeGen/LiveIntervals.h"
#include "llvm/CodeGen/LiveStacks.h"
#include "llvm/CodeGen/MachineOperand.h"
using namespace llvm;
#define DEBUG_TYPE "amdgpu-mark-last-scratch-load"
namespace {
class AMDGPUMarkLastScratchLoad : public MachineFunctionPass {
private:
LiveStacks *LS = nullptr;
LiveIntervals *LIS = nullptr;
SlotIndexes *SI = nullptr;
const SIInstrInfo *SII = nullptr;
public:
static char ID;
AMDGPUMarkLastScratchLoad() : MachineFunctionPass(ID) {
initializeAMDGPUMarkLastScratchLoadPass(*PassRegistry::getPassRegistry());
}
bool runOnMachineFunction(MachineFunction &MF) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<SlotIndexesWrapperPass>();
AU.addRequired<LiveIntervalsWrapperPass>();
AU.addRequired<LiveStacks>();
AU.setPreservesAll();
MachineFunctionPass::getAnalysisUsage(AU);
}
StringRef getPassName() const override {
return "AMDGPU Mark Last Scratch Load";
}
};
} // end anonymous namespace
bool AMDGPUMarkLastScratchLoad::runOnMachineFunction(MachineFunction &MF) {
if (skipFunction(MF.getFunction()))
return false;
const GCNSubtarget &ST = MF.getSubtarget<GCNSubtarget>();
if (ST.getGeneration() < AMDGPUSubtarget::GFX12)
return false;
LS = &getAnalysis<LiveStacks>();
LIS = &getAnalysis<LiveIntervalsWrapperPass>().getLIS();
SI = &getAnalysis<SlotIndexesWrapperPass>().getSI();
SII = ST.getInstrInfo();
SlotIndexes &Slots = *LIS->getSlotIndexes();
const unsigned NumSlots = LS->getNumIntervals();
if (NumSlots == 0) {
LLVM_DEBUG(dbgs() << "No live slots, skipping\n");
return false;
}
LLVM_DEBUG(dbgs() << LS->getNumIntervals() << " intervals\n");
bool Changed = false;
for (auto &[SS, LI] : *LS) {
for (const LiveRange::Segment &Segment : LI.segments) {
// Ignore segments that run to the end of basic block because in this case
// slot is still live at the end of it.
if (Segment.end.isBlock())
continue;
const int FrameIndex = Register::stackSlot2Index(LI.reg());
MachineInstr *LastLoad = nullptr;
MachineInstr *MISegmentEnd = SI->getInstructionFromIndex(Segment.end);
// If there is no instruction at this slot because it was deleted take the
// instruction from the next slot.
if (!MISegmentEnd) {
SlotIndex NextSlot = Slots.getNextNonNullIndex(Segment.end);
MISegmentEnd = SI->getInstructionFromIndex(NextSlot);
}
MachineInstr *MISegmentStart = SI->getInstructionFromIndex(Segment.start);
MachineBasicBlock *BB = MISegmentEnd->getParent();
// Start iteration backwards from segment end until the start of basic
// block or start of segment if it is in the same basic block.
auto End = BB->rend();
if (MISegmentStart && MISegmentStart->getParent() == BB)
End = MISegmentStart->getReverseIterator();
for (auto MI = MISegmentEnd->getReverseIterator(); MI != End; ++MI) {
int LoadFI = 0;
if (SII->isLoadFromStackSlot(*MI, LoadFI) && LoadFI == FrameIndex) {
LastLoad = &*MI;
break;
}
}
if (LastLoad && !LastLoad->memoperands_empty()) {
MachineMemOperand *MMO = *LastLoad->memoperands_begin();
MMO->setFlags(MOLastUse);
Changed = true;
LLVM_DEBUG(dbgs() << " Found last load: " << *LastLoad);
}
}
}
return Changed;
}
char AMDGPUMarkLastScratchLoad::ID = 0;
char &llvm::AMDGPUMarkLastScratchLoadID = AMDGPUMarkLastScratchLoad::ID;
INITIALIZE_PASS_BEGIN(AMDGPUMarkLastScratchLoad, DEBUG_TYPE,
"AMDGPU Mark last scratch load", false, false)
INITIALIZE_PASS_DEPENDENCY(SlotIndexesWrapperPass)
INITIALIZE_PASS_DEPENDENCY(LiveStacks)
INITIALIZE_PASS_END(AMDGPUMarkLastScratchLoad, DEBUG_TYPE,
"AMDGPU Mark last scratch load", false, false)
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