[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, 16 insertions, 10 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index b57004f7e12..19cfffd81c4 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -5033,22 +5033,28 @@ void CodeGenModule::AddVTableTypeMetadata(llvm::GlobalVariable *VTable,
   }
 }
 
+TargetAttr::ParsedTargetAttr CodeGenModule::filterFunctionTargetAttrs(const TargetAttr *TD) {
+  assert(TD != nullptr);
+  TargetAttr::ParsedTargetAttr ParsedAttr = TD->parse();
+
+  ParsedAttr.Features.erase(
+      llvm::remove_if(ParsedAttr.Features,
+                      [&](const std::string &Feat) {
+                        return !Target.isValidFeatureName(
+                            StringRef{Feat}.substr(1));
+                      }),
+      ParsedAttr.Features.end());
+  return ParsedAttr;
+}
+
+
 // Fills in the supplied string map with the set of target features for the
 // passed in function.
 void CodeGenModule::getFunctionFeatureMap(llvm::StringMap<bool> &FeatureMap,
                                           const FunctionDecl *FD) {
   StringRef TargetCPU = Target.getTargetOpts().CPU;
   if (const auto *TD = FD->getAttr<TargetAttr>()) {
-    // If we have a TargetAttr build up the feature map based on that.
-    TargetAttr::ParsedTargetAttr ParsedAttr = TD->parse();
-
-    ParsedAttr.Features.erase(
-        llvm::remove_if(ParsedAttr.Features,
-                        [&](const std::string &Feat) {
-                          return !Target.isValidFeatureName(
-                              StringRef{Feat}.substr(1));
-                        }),
-        ParsedAttr.Features.end());
+    TargetAttr::ParsedTargetAttr ParsedAttr = filterFunctionTargetAttrs(TD);
 
     // Make a copy of the features as passed on the command line into the
     // beginning of the additional features from the function to override.