[PATCH] D31806: [SimplifyLibCalls] Fix infinite loop with fast-math optimization.

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

gcc transforms the given C code to a call to expf(), just like LLVM, but then it looks like their inliner works a bit differently so the generated code ends up with a call to expf() rather than an infinite loop.  With your patch, LLVM also generates a call to expf().  This seems weird... does MinGW's C library actually have an expf() function?



================
Comment at: lib/Transforms/Utils/SimplifyLibCalls.cpp:935
+  // same name and signature as the float version of this call!
+  // e.g. float floorf(float val) { return (float) floor((double) val); }
+  if (!Callee->isIntrinsic()) {
----------------
You might want to explicitly note that MinGW is doing this; otherwise it seems like a weird hack, because it makes no sense to write an inline function like this if you have a standard-compliant C library.


================
Comment at: lib/Transforms/Utils/SimplifyLibCalls.cpp:945
+      if (FT->getReturnType()->isFloatTy() && (FT->getNumParams() == 1) &&
+          FT->getParamType(0)->isFloatTy())
+        return nullptr;
----------------
The FunctionType check doesn't seem necessary here.


================
Comment at: test/Transforms/Util/libcalls-fast-math-inf-loop.ll:1
+; RUN: opt -S -O2 -o - %s | FileCheck %s
+
----------------
Please don't use -O2 in tests... just test the specific pass you care about (in this case, instcombine).


https://reviews.llvm.org/D31806