[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, 10 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index 6c73a8cebdc..916051556a2 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -2330,9 +2330,19 @@ void CodeGenFunction::checkTargetFeatures(const CallExpr *E,
 
   } else if (TargetDecl->hasAttr<TargetAttr>()) {
     // Get the required features for the callee.
+
+    const TargetAttr *TD = TargetDecl->getAttr<TargetAttr>();
+    TargetAttr::ParsedTargetAttr ParsedAttr = CGM.filterFunctionTargetAttrs(TD);
+
     SmallVector<StringRef, 1> ReqFeatures;
     llvm::StringMap<bool> CalleeFeatureMap;
     CGM.getFunctionFeatureMap(CalleeFeatureMap, TargetDecl);
+
+    for (const auto &F : ParsedAttr.Features) {
+      if (F[0] == '+' && CalleeFeatureMap.lookup(F.substr(1)))
+        ReqFeatures.push_back(StringRef(F).substr(1));
+    }
+
     for (const auto &F : CalleeFeatureMap) {
       // Only positive features are "required".
       if (F.getValue())