diff options
Diffstat (limited to 'llvm/lib')
| -rw-r--r-- | llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp | 37 |
1 files changed, 23 insertions, 14 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp index b3366bb9888..f1a66816c4c 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp @@ -3734,15 +3734,7 @@ Instruction *InstCombiner::FoldFCmp_IntToFP_Cst(FCmpInst &I, IntegerType *IntTy = cast<IntegerType>(LHSI->getOperand(0)->getType()); - // Check to see that the input is converted from an integer type that is small - // enough that preserves all bits. TODO: check here for "known" sign bits. - // This would allow us to handle (fptosi (x >>s 62) to float) if x is i64 f.e. - unsigned InputSize = IntTy->getScalarSizeInBits(); - - // If this is a uitofp instruction, we need an extra bit to hold the sign. bool LHSUnsigned = isa<UIToFPInst>(LHSI); - if (LHSUnsigned) - ++InputSize; if (I.isEquality()) { FCmpInst::Predicate P = I.getPredicate(); @@ -3769,13 +3761,30 @@ Instruction *InstCombiner::FoldFCmp_IntToFP_Cst(FCmpInst &I, // equality compares as integer? } - // Comparisons with zero are a special case where we know we won't lose - // information. - bool IsCmpZero = RHS.isPosZero(); + // Check to see that the input is converted from an integer type that is small + // enough that preserves all bits. TODO: check here for "known" sign bits. + // This would allow us to handle (fptosi (x >>s 62) to float) if x is i64 f.e. + unsigned InputSize = IntTy->getScalarSizeInBits(); - // If the conversion would lose info, don't hack on this. - if ((int)InputSize > MantissaWidth && !IsCmpZero) - return nullptr; + // Following test does NOT adjust InputSize downwards for signed inputs, + // because the most negative value still requires all the mantissa bits + // to distinguish it from one less than that value. + if ((int)InputSize > MantissaWidth) { + // Conversion would lose accuracy. Check if loss can impact comparison. + int Exp = ilogb(RHS); + if (Exp == APFloat::IEK_Inf) { + int MaxExponent = ilogb(APFloat::getLargest(RHS.getSemantics())); + if (MaxExponent < (int)InputSize - !LHSUnsigned) + // Conversion could create infinity. + return nullptr; + } else { + // Note that if RHS is zero or NaN, then Exp is negative + // and first condition is trivially false. + if (MantissaWidth <= Exp && Exp <= (int)InputSize - !LHSUnsigned) + // Conversion could affect comparison. + return nullptr; + } + } // Otherwise, we can potentially simplify the comparison. We know that it // will always come through as an integer value and we know the constant is |
