From 1606fc0bf90fa984f335c7d9d7b56761afa0e67a Mon Sep 17 00:00:00 2001 From: Andrew Ng Date: Tue, 25 Apr 2017 12:36:14 +0000 Subject: [PATCH] [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 --- llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp | 18 +++++++ .../Transforms/Util/libcalls-fast-math-inf-loop.ll | 60 ++++++++++++++++++++++ 2 files changed, 78 insertions(+) create mode 100644 llvm/test/Transforms/Util/libcalls-fast-math-inf-loop.ll 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 @@ static Value *optimizeUnaryDoubleFP(CallInst *CI, IRBuilder<> &B, 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()); diff --git a/llvm/test/Transforms/Util/libcalls-fast-math-inf-loop.ll b/llvm/test/Transforms/Util/libcalls-fast-math-inf-loop.ll new file mode 100644 index 0000000..a351fe8 --- /dev/null +++ b/llvm/test/Transforms/Util/libcalls-fast-math-inf-loop.ll @@ -0,0 +1,60 @@ +; RUN: opt -S -instcombine -o - %s | FileCheck %s + +; Test that fast math lib call simplification of double math function to float +; equivalent doesn't occur when the calling function matches the float +; equivalent math function. Otherwise this can cause the generation of infinite +; loops when compiled with -O2/3 and fast math. + +; Test case C source: +; +; extern double exp(double x); +; inline float expf(float x) { return (float) exp((double) x); } +; float fn(float f) { return expf(f); } +; +; IR generated with command: +; +; clang -cc1 -O2 -ffast-math -emit-llvm -disable-llvm-passes -triple x86_64-unknown-unknown -o - + +target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128" +target triple = "x86_64-unknown-unknown" + +; Function Attrs: nounwind +define float @fn(float %f) #0 { +; CHECK: define float @fn( +; CHECK: call fast float @expf( + %f.addr = alloca float, align 4 + store float %f, float* %f.addr, align 4, !tbaa !1 + %1 = load float, float* %f.addr, align 4, !tbaa !1 + %call = call fast float @expf(float %1) #3 + ret float %call +} + +; Function Attrs: inlinehint nounwind readnone +define available_externally float @expf(float %x) #1 { +; CHECK: define available_externally float @expf( +; CHECK: fpext float +; CHECK: call fast double @exp( +; CHECK: fptrunc double + %x.addr = alloca float, align 4 + store float %x, float* %x.addr, align 4, !tbaa !1 + %1 = load float, float* %x.addr, align 4, !tbaa !1 + %conv = fpext float %1 to double + %call = call fast double @exp(double %conv) #3 + %conv1 = fptrunc double %call to float + ret float %conv1 +} + +; Function Attrs: nounwind readnone +declare double @exp(double) #2 + +attributes #0 = { nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-features"="+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" } +attributes #1 = { inlinehint nounwind readnone "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-features"="+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" } +attributes #2 = { nounwind readnone } + +!llvm.ident = !{!0} + +!0 = !{!"clang version 5.0.0"} +!1 = !{!2, !2, i64 0} +!2 = !{!"float", !3, i64 0} +!3 = !{!"omnipotent char", !4, i64 0} +!4 = !{!"Simple C/C++ TBAA"} -- 2.7.4