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[DirectX] Legalize Freeze instruction (#136043)

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fixes #135719

LLVM 3.7 did not have a freeze instruction
Further this instruction is really only used as syntactic sugar
in LLVM's optimizer passes to not aggressively optimize things that
could be undef or poison ie x*2 to x+x.
Most backends treat it as a no-op so we will do the same
by removing it and replacing its uses with its input.
This commit is contained in:
Farzon Lotfi 2025-04-17 12:02:05 -04:00 committed by GitHub
parent 8311620933
commit 168092e2ba
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2 changed files with 29 additions and 0 deletions
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12
llvm/lib/Target/DirectX/DXILLegalizePass.cpp
View File

@ -20,6 +20,17 @@
using namespace llvm;
static void legalizeFreeze(Instruction &I,
SmallVectorImpl<Instruction *> &ToRemove,
DenseMap<Value *, Value *>) {
auto *FI = dyn_cast<FreezeInst>(&I);
if (!FI)
return;
FI->replaceAllUsesWith(FI->getOperand(0));
ToRemove.push_back(FI);
}
static void fixI8TruncUseChain(Instruction &I,
SmallVectorImpl<Instruction *> &ToRemove,
DenseMap<Value *, Value *> &ReplacedValues) {
@ -169,6 +180,7 @@ private:
void initializeLegalizationPipeline() {
LegalizationPipeline.push_back(fixI8TruncUseChain);
LegalizationPipeline.push_back(downcastI64toI32InsertExtractElements);
LegalizationPipeline.push_back(legalizeFreeze);
}
};

17
llvm/test/CodeGen/DirectX/legalize-freeze.ll Normal file
View File

@ -0,0 +1,17 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
; RUN: opt -S -passes='dxil-legalize' -mtriple=dxil-pc-shadermodel6.3-library %s | FileCheck %s
define i32 @test_remove_freeze(i32 %x) {
; CHECK-LABEL: define i32 @test_remove_freeze(
; CHECK-SAME: i32 [[X:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[Y:%.*]] = add i32 [[X]], 1
; CHECK-NEXT: ret i32 [[Y]]
;
entry:
%f = freeze i32 %x
%y = add i32 %f, 1
ret i32 %y
}