[InjectTLIMappings] Use StringRef instead of std::string for FN name.

[nadav]

Summary

Remove thousands of std::string instances in a helper function that is frequently called. In the common case we don't need to construct an std::string instance when we can just pass the StringRef to TTI.

All of the clang-check tests pass. I discovered this with a Facebook-internal tool.

[fhahn]

LGTM thanks. It might be good to adjust the commit message to be a bit more descriptive, e.g. something like [InjectTLIMappings] Use StringRef instead of std::string for FN name.

llvm/lib/Transforms/Utils/InjectTLIMappings.cpp

80–81

It might be worth spelling out StringRef here, as the return type is not completely obvious.

86

nit: unrelated whitespace change.

[nadav]

Thank you. I will make the changes and try to commit the patch.

[fhahn]

@nadav I think the change landed in rG8f0a8ed44e27 and the revision can be closed now, right?

It looks like you included the URL to the review in the commit message, but I think you need to put a something like Differential Revision: https://reviews.llvm.org/D83797 in the message for Phabricator to automatically close the revision.

llvm/lib/Transforms/Utils/InjectTLIMappings.cpp

   if (CI.isNoBuiltin() || !CI.getCalledFunction())
     return;
 
-  const std::string ScalarName = std::string(CI.getCalledFunction()->getName());
+  auto NameRef = CI.getCalledFunction()->getName();
+
   // Nothing to be done if the TLI thinks the function is not
   // vectorizable.
-  if (!TLI.isFunctionVectorizable(ScalarName))
+  if (!TLI.isFunctionVectorizable(NameRef))
     return;
+
+  const std::string ScalarName = std::string(NameRef);
   SmallVector<std::string, 8> Mappings;
   VFABI::getVectorVariantNames(CI, Mappings);
   Module *M = CI.getModule();