diff options
| -rw-r--r-- | lib/Transforms/InstCombine/InstCombineSelect.cpp | 28 | ||||
| -rw-r--r-- | test/Transforms/InstCombine/fcmp-select.ll | 53 |
2 files changed, 76 insertions, 5 deletions
diff --git a/lib/Transforms/InstCombine/InstCombineSelect.cpp b/lib/Transforms/InstCombine/InstCombineSelect.cpp index 7807d9a..2fc9325 100644 --- a/lib/Transforms/InstCombine/InstCombineSelect.cpp +++ b/lib/Transforms/InstCombine/InstCombineSelect.cpp @@ -539,9 +539,18 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) { !CFPf->getValueAPF().isZero())) return ReplaceInstUsesWith(SI, FalseVal); } - // Transform (X != Y) ? X : Y -> X - if (FCI->getPredicate() == FCmpInst::FCMP_ONE) + // Transform (X une Y) ? X : Y -> X + if (FCI->getPredicate() == FCmpInst::FCMP_UNE) { + // This is not safe in general for floating point: + // consider X== -0, Y== +0. + // It becomes safe if either operand is a nonzero constant. + ConstantFP *CFPt, *CFPf; + if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && + !CFPt->getValueAPF().isZero()) || + ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && + !CFPf->getValueAPF().isZero())) return ReplaceInstUsesWith(SI, TrueVal); + } // NOTE: if we wanted to, this is where to detect MIN/MAX } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){ @@ -557,9 +566,18 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) { !CFPf->getValueAPF().isZero())) return ReplaceInstUsesWith(SI, FalseVal); } - // Transform (X != Y) ? Y : X -> Y - if (FCI->getPredicate() == FCmpInst::FCMP_ONE) - return ReplaceInstUsesWith(SI, TrueVal); + // Transform (X une Y) ? Y : X -> Y + if (FCI->getPredicate() == FCmpInst::FCMP_UNE) { + // This is not safe in general for floating point: + // consider X== -0, Y== +0. + // It becomes safe if either operand is a nonzero constant. + ConstantFP *CFPt, *CFPf; + if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && + !CFPt->getValueAPF().isZero()) || + ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && + !CFPf->getValueAPF().isZero())) + return ReplaceInstUsesWith(SI, TrueVal); + } // NOTE: if we wanted to, this is where to detect MIN/MAX } // NOTE: if we wanted to, this is where to detect ABS diff --git a/test/Transforms/InstCombine/fcmp-select.ll b/test/Transforms/InstCombine/fcmp-select.ll new file mode 100644 index 0000000..e04ab3e --- /dev/null +++ b/test/Transforms/InstCombine/fcmp-select.ll @@ -0,0 +1,53 @@ +; RUN: opt < %s -instcombine -S | FileCheck %s + +; x != y ? x : y -> x if it's the right kind of != and at least +; one of x and y is not negative zero. + +; CHECK: f0 +; CHECK: ret double %x +define double @f0(double %x) nounwind readnone { +entry: + %cmp = fcmp une double %x, -1.0 + %cond = select i1 %cmp, double %x, double -1.0 + ret double %cond +} +; CHECK: f1 +; CHECK: ret double -1.000000e+00 +define double @f1(double %x) nounwind readnone { +entry: + %cmp = fcmp une double %x, -1.0 + %cond = select i1 %cmp, double -1.0, double %x + ret double %cond +} +; CHECK: f2 +; CHECK: ret double %cond +define double @f2(double %x, double %y) nounwind readnone { +entry: + %cmp = fcmp une double %x, %y + %cond = select i1 %cmp, double %x, double %y + ret double %cond +} +; CHECK: f3 +; CHECK: ret double %cond +define double @f3(double %x, double %y) nounwind readnone { +entry: + %cmp = fcmp une double %x, %y + %cond = select i1 %cmp, double %y, double %x + ret double %cond +} +; CHECK: f4 +; CHECK: ret double %cond +define double @f4(double %x) nounwind readnone { +entry: + %cmp = fcmp one double %x, -1.0 + %cond = select i1 %cmp, double %x, double -1.0 + ret double %cond +} +; CHECK: f5 +; CHECK: ret double %cond +define double @f5(double %x) nounwind readnone { +entry: + %cmp = fcmp one double %x, -1.0 + %cond = select i1 %cmp, double -1.0, double %x + ret double %cond +} |