[SimplifyLibCalls] Fix infinite loop with fast-math optimization.
One of the fast-math optimizations is to replace calls to standard double
functions with their float equivalents, e.g. exp -> expf. However, this can
cause infinite loops for the following:
float expf(float val) { return (float) exp((double) val); }
A similar inline declaration exists in the MinGW-w64 math.h header file which
when compiled with -O2/3 and fast-math generates infinite loops.
So this fix checks that the calling function to the standard double function
that is being replaced does not match the float equivalent.
Differential Revision: https://reviews.llvm.org/D31806
llvm-svn: 301304
diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index 956bd08..4818939 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -926,6 +926,24 @@
if (V == nullptr)
return nullptr;
+ // If call isn't an intrinsic, check that it isn't within a function with the
+ // same name as the float version of this call.
+ //
+ // e.g. inline float expf(float val) { return (float) exp((double) val); }
+ //
+ // A similar such definition exists in the MinGW-w64 math.h header file which
+ // when compiled with -O2 -ffast-math causes the generation of infinite loops
+ // where expf is called.
+ if (!Callee->isIntrinsic()) {
+ const Function *F = CI->getFunction();
+ StringRef FName = F->getName();
+ StringRef CalleeName = Callee->getName();
+ if ((FName.size() == (CalleeName.size() + 1)) &&
+ (FName.back() == 'f') &&
+ FName.startswith(CalleeName))
+ return nullptr;
+ }
+
// Propagate fast-math flags from the existing call to the new call.
IRBuilder<>::FastMathFlagGuard Guard(B);
B.setFastMathFlags(CI->getFastMathFlags());