transform fmin/fmax calls when possible (PR24314)
If we can ignore NaNs, fmin/fmax libcalls can become compare and select
(this is what we turn std::min / std::max into).
This IR should then be optimized in the backend to whatever is best for
any given target. Eg, x86 can use minss/maxss instructions.
This should solve PR24314:
https://llvm.org/bugs/show_bug.cgi?id=24314
Differential Revision: http://reviews.llvm.org/D11866
llvm-svn: 245187
diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index bb03c98..50513642 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1184,6 +1184,60 @@
return Ret;
}
+Value *LibCallSimplifier::optimizeFMinFMax(CallInst *CI, IRBuilder<> &B) {
+ // If we can shrink the call to a float function rather than a double
+ // function, do that first.
+ Function *Callee = CI->getCalledFunction();
+ if ((Callee->getName() == "fmin" && TLI->has(LibFunc::fminf)) ||
+ (Callee->getName() == "fmax" && TLI->has(LibFunc::fmaxf))) {
+ Value *Ret = optimizeBinaryDoubleFP(CI, B);
+ if (Ret)
+ return Ret;
+ }
+
+ // Make sure this has 2 arguments of FP type which match the result type.
+ FunctionType *FT = Callee->getFunctionType();
+ if (FT->getNumParams() != 2 || FT->getReturnType() != FT->getParamType(0) ||
+ FT->getParamType(0) != FT->getParamType(1) ||
+ !FT->getParamType(0)->isFloatingPointTy())
+ return nullptr;
+
+ // FIXME: For finer-grain optimization, we need intrinsics to have the same
+ // fast-math flag decorations that are applied to FP instructions. For now,
+ // we have to rely on the function-level attributes to do this optimization
+ // because there's no other way to express that the calls can be relaxed.
+ IRBuilder<true, ConstantFolder,
+ IRBuilderDefaultInserter<true> >::FastMathFlagGuard Guard(B);
+ FastMathFlags FMF;
+ Function *F = CI->getParent()->getParent();
+ Attribute Attr = F->getFnAttribute("unsafe-fp-math");
+ if (Attr.getValueAsString() == "true") {
+ // Unsafe algebra sets all fast-math-flags to true.
+ FMF.setUnsafeAlgebra();
+ } else {
+ // At a minimum, no-nans-fp-math must be true.
+ Attr = F->getFnAttribute("no-nans-fp-math");
+ if (Attr.getValueAsString() != "true")
+ return nullptr;
+ // No-signed-zeros is implied by the definitions of fmax/fmin themselves:
+ // "Ideally, fmax would be sensitive to the sign of zero, for example
+ // fmax(−0. 0, +0. 0) would return +0; however, implementation in software
+ // might be impractical."
+ FMF.setNoSignedZeros();
+ FMF.setNoNaNs();
+ }
+ B.SetFastMathFlags(FMF);
+
+ // We have a relaxed floating-point environment. We can ignore NaN-handling
+ // and transform to a compare and select. We do not have to consider errno or
+ // exceptions, because fmin/fmax do not have those.
+ Value *Op0 = CI->getArgOperand(0);
+ Value *Op1 = CI->getArgOperand(1);
+ Value *Cmp = Callee->getName().startswith("fmin") ?
+ B.CreateFCmpOLT(Op0, Op1) : B.CreateFCmpOGT(Op0, Op1);
+ return B.CreateSelect(Cmp, Op0, Op1);
+}
+
Value *LibCallSimplifier::optimizeSqrt(CallInst *CI, IRBuilder<> &B) {
Function *Callee = CI->getCalledFunction();
@@ -2110,11 +2164,16 @@
return optimizeUnaryDoubleFP(CI, Builder, true);
return nullptr;
case LibFunc::copysign:
- case LibFunc::fmin:
- case LibFunc::fmax:
if (hasFloatVersion(FuncName))
return optimizeBinaryDoubleFP(CI, Builder);
return nullptr;
+ case LibFunc::fminf:
+ case LibFunc::fmin:
+ case LibFunc::fminl:
+ case LibFunc::fmaxf:
+ case LibFunc::fmax:
+ case LibFunc::fmaxl:
+ return optimizeFMinFMax(CI, Builder);
default:
return nullptr;
}