[clang] [clang][NVPTX] exclude feature attributes from target-features (PR #215451)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-codegen

Author: Alex MacLean (AlexMaclean)

<details>
<summary>Changes</summary>

This info is already carried in `target-cpu` and the fact that these named features exist at all is something I hope to change. 

---
Full diff: https://github.com/llvm/llvm-project/pull/215451.diff


3 Files Affected:

- (modified) clang/lib/Basic/Targets/NVPTX.cpp (+6) 
- (modified) clang/lib/CodeGen/CodeGenModule.cpp (+5-3) 
- (modified) clang/test/CodeGen/nvptx_attributes.c (+1-1) 


``````````diff
diff --git a/clang/lib/Basic/Targets/NVPTX.cpp b/clang/lib/Basic/Targets/NVPTX.cpp
index 11577b75236a6..04b95dd19ed05 100644
--- a/clang/lib/Basic/Targets/NVPTX.cpp
+++ b/clang/lib/Basic/Targets/NVPTX.cpp
@@ -66,6 +66,12 @@ NVPTXTargetInfo::NVPTXTargetInfo(const llvm::Triple &Triple,
   NoAsmVariants = true;
   GPU = OffloadArch::getUnused();
 
+  // Architectures are in the feature map only to gate builtins; the backend
+  // takes the architecture from `target-cpu`.
+#define NVPTX_GPU(NAME, KIND, VIRTUAL, SM_ID, MIN_VER, MAX_VER, SUFFIX)        \
+  ReadOnlyFeatures.insert(NAME);
+#include "llvm/TargetParser/NVPTXTargetParser.def"
+
   // PTX supports f16 as a fundamental type.
   HasFastHalfType = true;
   HasFloat16 = true;
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 5ed5385c90f26..0c0d1c272b386 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -3417,9 +3417,11 @@ bool CodeGenModule::GetCPUAndFeaturesAttributes(GlobalDecl GD,
     llvm::erase_if(Features, [&](const std::string& F) {
        return getTarget().isReadOnlyFeature(F.substr(1));
     });
-    llvm::sort(Features);
-    Attrs.addAttribute("target-features", llvm::join(Features, ","));
-    AddedAttr = true;
+    if (!Features.empty()) {
+      llvm::sort(Features);
+      Attrs.addAttribute("target-features", llvm::join(Features, ","));
+      AddedAttr = true;
+    }
   }
   // Add metadata for AArch64 Function Multi Versioning.
   if (getTarget().getTriple().isAArch64()) {
diff --git a/clang/test/CodeGen/nvptx_attributes.c b/clang/test/CodeGen/nvptx_attributes.c
index c49a68b89bc64..fbba84ff05d5a 100644
--- a/clang/test/CodeGen/nvptx_attributes.c
+++ b/clang/test/CodeGen/nvptx_attributes.c
@@ -16,7 +16,7 @@ __attribute__((nvptx_kernel)) void foo(int *ret) {
 }
 
 //.
-// CHECK: attributes #[[ATTR0]] = { convergent noinline nounwind optnone "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="sm_61" "target-features"="+sm_61" }
+// CHECK: attributes #[[ATTR0]] = { convergent noinline nounwind optnone "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="sm_61" }
 //.
 // CHECK: [[META0:![0-9]+]] = !{!"{{.*}}clang version {{.*}}"}
 //.

``````````

</details>


https://github.com/llvm/llvm-project/pull/215451