release/19.x: [WebAssembly] Fix feature coalescing (#110647) #112431
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@tlively What do you think about merging this PR to the release branch? |
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@llvm/pr-subscribers-backend-webassembly Author: None (llvmbot) ChangesBackport 5a7b79c Requested by: @nikic Full diff: https://github.com/llvm/llvm-project/pull/112431.diff 1 Files Affected:
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
index 23539a5f4b26f1..ac9e6d5a90cb3c 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
@@ -202,8 +202,7 @@ class CoalesceFeaturesAndStripAtomics final : public ModulePass {
bool runOnModule(Module &M) override {
FeatureBitset Features = coalesceFeatures(M);
- std::string FeatureStr =
- getFeatureString(Features, WasmTM->getTargetFeatureString());
+ std::string FeatureStr = getFeatureString(Features);
WasmTM->setTargetFeatureString(FeatureStr);
for (auto &F : M)
replaceFeatures(F, FeatureStr);
@@ -241,17 +240,14 @@ class CoalesceFeaturesAndStripAtomics final : public ModulePass {
return Features;
}
- static std::string getFeatureString(const FeatureBitset &Features,
- StringRef TargetFS) {
+ static std::string getFeatureString(const FeatureBitset &Features) {
std::string Ret;
for (const SubtargetFeatureKV &KV : WebAssemblyFeatureKV) {
if (Features[KV.Value])
Ret += (StringRef("+") + KV.Key + ",").str();
+ else
+ Ret += (StringRef("-") + KV.Key + ",").str();
}
- SubtargetFeatures TF{TargetFS};
- for (std::string const &F : TF.getFeatures())
- if (!SubtargetFeatures::isEnabled(F))
- Ret += F + ",";
return Ret;
}
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tlively
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This fixes a problem introduced in llvm#80094. That PR copied negative features from the TargetMachine to the end of the feature string. This is not correct, because even if we have a baseline TM of say `-simd128`, but a function with `+simd128`, the coalesced feature string should have `+simd128`, not `-simd128`. To address the original motivation of that PR, we should instead explicitly materialize the negative features in the target feature string, so that explicitly disabled default features are honored. Unfortunately, there doesn't seem to be any way to actually test this using llc, because `-mattr` appends the specified features to the end of the `"target-features"` attribute. I've tested this locally by making it prepend the features instead. (cherry picked from commit 5a7b79c)
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@nikic (or anyone else). If you would like to add a note about this fix in the release notes (completely optional). Please reply to this comment with a one or two sentence description of the fix. When you are done, please add the release:note label to this PR. |
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Backport 5a7b79c
Requested by: @nikic