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Remove llvm::shouldOptForSize() from Utils.h #112630

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Merged
merged 2 commits into from
Oct 29, 2024
Merged

Remove llvm::shouldOptForSize() from Utils.h #112630

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e2cd7f9
Remove llvm::shouldOptForSize()
ellishg Oct 16, 2024
fa93c01
Merge branch 'main' into remove-optforsize
ellishg Oct 29, 2024
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9 changes: 7 additions & 2 deletions llvm/include/llvm/CodeGen/GlobalISel/GIMatchTableExecutor.h
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,7 @@
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGenTypes/LowLevelType.h"
#include "llvm/IR/Function.h"
#include "llvm/Transforms/Utils/SizeOpts.h"
#include <bitset>
#include <cstddef>
#include <cstdint>
Expand Down Expand Up @@ -635,8 +636,12 @@ class GIMatchTableExecutor {

bool shouldOptForSize(const MachineFunction *MF) const {
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@kyulee-com kyulee-com Oct 28, 2024 •
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I don't think this is from your change, but it's a bit confusing how shouldOptForSize differs from llvm::shouldOptimizeForSize. I guess this is specifically used for GISel, and as long as the current processing block is optimized for size, we consider this function optimized for size? But don't we derive this check for a block by checking its parent function? Basically, my understanding is that even if shouldOptimizeForSize for a function is false, shouldOptimizeForSize for a block that belongs to the function may be true. Here, it doesn't seem like that's the case.

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@ellishg ellishg Oct 28, 2024

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Yes, I would like to remove this too, but this caused some build errors because of generated code. In fact, some implementors don't even check PGO.

llvm-project/llvm/include/llvm/CodeGen/FastISel.h

Lines 520 to 523 in 66bbbf2

bool shouldOptForSize(const MachineFunction *MF) const {
// TODO: Implement PGSO.
return MF->getFunction().hasOptSize();
}

Since I'm less familiar with ISel, I thought I'd leave this alone for now.

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@kyulee-com kyulee-com Oct 28, 2024

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It appears that ISel generally prioritizes optimization for size. Since the shouldOptForSize derives its result from the current processing block, the outcome may not be consistent depending on which blocks are being processed, which is counterintuitive.
Upon examining another usage of DAGISel below, I believe this API is actually asking whether the current function should be optimized for size based on the current processing block or DAG.

llvm-project/llvm/include/llvm/CodeGen/SelectionDAGISel.h

Lines 396 to 398 in 66bbbf2

bool shouldOptForSize(const MachineFunction *MF) const {
return CurDAG->shouldOptForSize();
}

So, we should keep this way on this context.

const auto &F = MF->getFunction();
return F.hasOptSize() || F.hasMinSize() ||
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@arsenm arsenm Oct 17, 2024

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Lost the hasMinSize check?

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@ellishg ellishg Oct 28, 2024

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As mentioned above (but got lost in the changes), F.hasOptSize() already calls hasMinSize().

llvm-project/llvm/include/llvm/IR/Function.h

Lines 707 to 709 in 927af63

bool hasOptSize() const {
return hasFnAttribute(Attribute::OptimizeForSize) || hasMinSize();
}

(PSI && BFI && CurMBB && llvm::shouldOptForSize(*CurMBB, PSI, BFI));
if (F.hasOptSize())
return true;
if (CurMBB)
if (auto *BB = CurMBB->getBasicBlock())
return llvm::shouldOptimizeForSize(BB, PSI, BFI);
return false;
}

public:
Expand Down
4 changes: 0 additions & 4 deletions llvm/include/llvm/CodeGen/GlobalISel/Utils.h
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Expand Up @@ -542,10 +542,6 @@ bool isConstFalseVal(const TargetLowering &TLI, int64_t Val, bool IsVector,
/// TargetBooleanContents.
int64_t getICmpTrueVal(const TargetLowering &TLI, bool IsVector, bool IsFP);

/// Returns true if the given block should be optimized for size.
bool shouldOptForSize(const MachineBasicBlock &MBB, ProfileSummaryInfo *PSI,
BlockFrequencyInfo *BFI);

using SmallInstListTy = GISelWorkList<4>;
void saveUsesAndErase(MachineInstr &MI, MachineRegisterInfo &MRI,
LostDebugLocObserver *LocObserver,
Expand Down
5 changes: 0 additions & 5 deletions llvm/lib/CodeGen/GlobalISel/Utils.cpp
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Expand Up @@ -1619,11 +1619,6 @@ int64_t llvm::getICmpTrueVal(const TargetLowering &TLI, bool IsVector,
llvm_unreachable("Invalid boolean contents");
}

bool llvm::shouldOptForSize(const MachineBasicBlock &MBB,
ProfileSummaryInfo *PSI, BlockFrequencyInfo *BFI) {
return llvm::shouldOptimizeForSize(MBB.getBasicBlock(), PSI, BFI);
}

void llvm::saveUsesAndErase(MachineInstr &MI, MachineRegisterInfo &MRI,
LostDebugLocObserver *LocObserver,
SmallInstListTy &DeadInstChain) {
Expand Down
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