[llvm] [WebAssembly] avoid to enable explicit disabled feature (PR #80094)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-webassembly

Author: Congcong Cai (HerrCai0907)

<details>
<summary>Changes</summary>

In `CoalesceFeaturesAndStripAtomics`, feature string is converted to FeatureBitset and back to feature string. It will lose information about explicit diasbled features.

---
Full diff: https://github.com/llvm/llvm-project/pull/80094.diff


2 Files Affected:

- (modified) llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp (+8-2) 
- (added) llvm/test/CodeGen/WebAssembly/disable-feature.ll (+22) 


``````````diff
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
index 2db1b6493cc47..0aadc6aca228d 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
@@ -200,7 +200,8 @@ class CoalesceFeaturesAndStripAtomics final : public ModulePass {
   bool runOnModule(Module &M) override {
     FeatureBitset Features = coalesceFeatures(M);
 
-    std::string FeatureStr = getFeatureString(Features);
+    std::string FeatureStr =
+        getFeatureString(Features, WasmTM->getTargetFeatureString());
     WasmTM->setTargetFeatureString(FeatureStr);
     for (auto &F : M)
       replaceFeatures(F, FeatureStr);
@@ -238,12 +239,17 @@ class CoalesceFeaturesAndStripAtomics final : public ModulePass {
     return Features;
   }
 
-  std::string getFeatureString(const FeatureBitset &Features) {
+  static std::string getFeatureString(const FeatureBitset &Features,
+                                      StringRef TargetFS) {
     std::string Ret;
     for (const SubtargetFeatureKV &KV : WebAssemblyFeatureKV) {
       if (Features[KV.Value])
         Ret += (StringRef("+") + KV.Key + ",").str();
     }
+    SubtargetFeatures TF{TargetFS};
+    for (std::string const &F : TF.getFeatures())
+      if (!SubtargetFeatures::isEnabled(F))
+        Ret += F;
     return Ret;
   }
 
diff --git a/llvm/test/CodeGen/WebAssembly/disable-feature.ll b/llvm/test/CodeGen/WebAssembly/disable-feature.ll
new file mode 100644
index 0000000000000..a9b07e2aaed5d
--- /dev/null
+++ b/llvm/test/CodeGen/WebAssembly/disable-feature.ll
@@ -0,0 +1,22 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -mattr=-sign-ext | FileCheck %s
+
+target triple = "wasm32-unknown-unknown"
+
+define i8 @ashr(i8 %v, i8 %x) {
+; CHECK-LABEL: ashr:
+; CHECK:         .functype ashr (i32, i32) -> (i32)
+; CHECK-NEXT:  # %bb.0:
+; CHECK-NEXT:    local.get 0
+; CHECK-NEXT:    i32.const 24
+; CHECK-NEXT:    i32.shl
+; CHECK-NEXT:    i32.const 24
+; CHECK-NEXT:    i32.shr_s
+; CHECK-NEXT:    local.get 1
+; CHECK-NEXT:    i32.const 255
+; CHECK-NEXT:    i32.and
+; CHECK-NEXT:    i32.shr_s
+; CHECK-NEXT:    # fallthrough-return
+  %a = ashr i8 %v, %x
+  ret i8 %a
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/80094