[CodeGen] Improve diagnostics related to target attributes

Summary:
When requirement imposed by __target__ attributes on functions
are not satisfied, prefer printing those requirements, which
are explicitly mentioned in the attributes.

This makes such messages more useful, e.g. printing avx512f instead of avx2
in the following scenario:

```
$ cat foo.c
static inline void __attribute__((__always_inline__, __target__("avx512f")))
x(void)
{
}

int main(void)
{
            x();
}
$ clang foo.c
foo.c:7:2: error: always_inline function 'x' requires target feature 'avx2', but would be inlined into function 'main' that is compiled without support for 'avx2'
        x();
    ^
1 error generated.
```

bugzilla: https://bugs.llvm.org/show_bug.cgi?id=37338

Reviewers: craig.topper, echristo, dblaikie

Reviewed By: craig.topper, echristo

Differential Revision: https://reviews.llvm.org/D46541

llvm-svn: 334174

1 files changed, 4 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
index 961bae324d3..89823982ac2 100644
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -1089,6 +1089,10 @@ public:
   /// It's up to you to ensure that this is safe.
   void AddDefaultFnAttrs(llvm::Function &F);
 
+  /// Parses the target attributes passed in, and returns only the ones that are
+  /// valid feature names.
+  TargetAttr::ParsedTargetAttr filterFunctionTargetAttrs(const TargetAttr *TD);
+
   // Fills in the supplied string map with the set of target features for the
   // passed in function.
   void getFunctionFeatureMap(llvm::StringMap<bool> &FeatureMap,