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[WebAssembly] Remove FAKE_USEs before ExplicitLocals #160228

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Merged
merged 2 commits into from
Sep 23, 2025
Merged

[WebAssembly] Remove FAKE_USEs before ExplicitLocals #160228

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f167fc8
[WebAssembly] Remove FAKE_USEs before ExplicitLocals
aheejin Sep 23, 2025
ebd82bc
clang-format
aheejin Sep 23, 2025
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14 changes: 14 additions & 0 deletions llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -216,6 +216,18 @@ static MachineInstr *findStartOfTree(MachineOperand &MO,
return Def;
}

// FAKE_USEs are no-ops, so remove them here so that the values used by them
// will be correctly dropped later.
static void removeFakeUses(MachineFunction &MF) {
SmallVector<MachineInstr *> ToDelete;
for (auto &MBB : MF)
for (auto &MI : MBB)
if (MI.isFakeUse())
ToDelete.push_back(&MI);
for (auto *MI : ToDelete)
MI->eraseFromParent();
}

bool WebAssemblyExplicitLocals::runOnMachineFunction(MachineFunction &MF) {
LLVM_DEBUG(dbgs() << "********** Make Locals Explicit **********\n"
"********** Function: "
Expand All @@ -226,6 +238,8 @@ bool WebAssemblyExplicitLocals::runOnMachineFunction(MachineFunction &MF) {
WebAssemblyFunctionInfo &MFI = *MF.getInfo<WebAssemblyFunctionInfo>();
const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();

removeFakeUses(MF);

// Map non-stackified virtual registers to their local ids.
DenseMap<unsigned, unsigned> Reg2Local;

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15 changes: 15 additions & 0 deletions llvm/test/CodeGen/WebAssembly/fake-use.ll
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@@ -0,0 +1,15 @@
; RUN: llc < %s | llvm-mc -triple=wasm32-unknown-unknown
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llvm-mc runs the type checker. Without this patch this wouldn't succeed.


target triple = "wasm32-unknown-unknown"

define void @fake_use_test() {
%t = call i32 @foo()
tail call void (...) @llvm.fake.use(i32 %t)
ret void
}

declare void @foo()
; Function Attrs: mustprogress nocallback nofree nosync nounwind willreturn memory(inaccessiblemem: readwrite)
declare void @llvm.fake.use(...) #0

attributes #0 = { mustprogress nocallback nofree nosync nounwind willreturn memory(inaccessiblemem: readwrite) }
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