[clang] [CIR] Implement function target/tune attrs and FMV metadata. (PR #195813)

[via cfe-commits]

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@@ -770,7 +770,46 @@ bool CIRGenModule::getCPUAndFeaturesAttributes(
   const auto *tc = fd ? fd->getAttr<TargetClonesAttr>() : nullptr;
   bool addedAttr = false;
   if (td || tv || sd || tc) {
-    assert(!cir::MissingFeatures::opFuncMultiVersioning());
+    llvm::StringMap<bool> featureMap;
+    astContext.getFunctionFeatureMap(featureMap, gd);
+
+    // Now add the target-cpu and target-features to the function.
+    // While we populated the feature map above, we still need to
+    // get and parse the target/target_clones attribute so we can
+    // get the cpu for the function.
+    llvm::StringRef featureStr = td ? td->getFeaturesStr() : llvm::StringRef();
+    if (tc && (getTriple().isOSAIX() || getTriple().isX86()))
+      featureStr = tc->getFeatureStr(gd.getMultiVersionIndex());
+    if (!featureStr.empty()) {
+      clang::ParsedTargetAttr parsedAttr =
+          getTarget().parseTargetAttr(featureStr);
+      if (!parsedAttr.CPU.empty() &&
+          getTarget().isValidCPUName(parsedAttr.CPU)) {
+        targetCPU = parsedAttr.CPU;
+        tuneCPU = ""; // Clear the tune CPU.
+      }
+      if (!parsedAttr.Tune.empty() &&
+          getTarget().isValidCPUName(parsedAttr.Tune))
+        tuneCPU = parsedAttr.Tune;
+    }
+
+    if (sd) {
+      // Apply the given CPU name as the 'tune-cpu' so that the optimizer can
+      // favor this processor.
+      tuneCPU = sd->getCPUName(gd.getMultiVersionIndex())->getName();
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skc7 wrote:

Checked `Sema::checkNonMultiVersionCompatAttributes` (clang/lib/Sema/SemaDecl.cpp) and seems it rejects combining `cpu_specific` with target / target_version / target_clones on the same decl, so when sd is set the only thing, this override is the command-line `-tune-cpu` default that tuneCPU was initialized with at the top of the function. Code logic here follows OGCG in `CodeGenModule.cpp`

https://github.com/llvm/llvm-project/pull/195813