[PATCH] D45180: libcalls must check for "RtLibUseGOT" metadata during simplification

[Eli Friedman via Phabricator via llvm-commits]

efriedma added inline comments.


================
Comment at: lib/Transforms/Utils/BuildLibCalls.cpp:991
   if (File->getType()->isPointerTy())
-    inferLibFuncAttributes(*M->getFunction("fputc"), *TLI);
+    inferLibFuncAttributes(*M->getFunction("fputc"), *TLI, M);
   Char = B.CreateIntCast(Char, B.getInt32Ty(), /*isSigned*/true,
----------------
tmsriram wrote:
> efriedma wrote:
> > The "if (File->getType()->isPointerTy())" here is suspicious... I think we always need to honor the RtLibUseGOT metadata?
> Good catch, thanks!  Looking at the other functions only the F{PutS, Putc,Write}  functions have this where it is safe to tag the param values with no capture.  When would this condition  File->getType()->isPointerTy() be false?  
Never, I think?  At least, I can't come up with a case where it would be false; all the SimplifyLibCalls transforms should call isValidProtoForLibFunc, which should check that FILE* parameters are pointers.

That said, there is a related problem here; we don't ever check that the function returned by `M->getFunction("fputc")` has the expected signature, so this could crash if there's an existing function named fputc with the wrong signature.  (Defining a function like that has undefined behavior, so it's unlikely to come up in practice, but we still shouldn't crash.)


https://reviews.llvm.org/D45180