diff options
Diffstat (limited to 'llvm/lib')
| -rw-r--r-- | llvm/lib/Target/README.txt | 11 | ||||
| -rw-r--r-- | llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp | 31 |
2 files changed, 31 insertions, 11 deletions
diff --git a/llvm/lib/Target/README.txt b/llvm/lib/Target/README.txt index 90afe3640ce..4d7ee08de1d 100644 --- a/llvm/lib/Target/README.txt +++ b/llvm/lib/Target/README.txt @@ -906,17 +906,6 @@ The expression should optimize to something like //===---------------------------------------------------------------------===// -From GCC Bug 3756: -int -pn (int n) -{ - return (n >= 0 ? 1 : -1); -} -Should combine to (n >> 31) | 1. Currently not optimized with "clang --emit-llvm-bc | opt -std-compile-opts | llc". - -//===---------------------------------------------------------------------===// - void a(int variable) { if (variable == 4 || variable == 6) diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp index c958cde0917..c44fe9db6e3 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp @@ -329,6 +329,37 @@ Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI, } } + // Transform (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 - C1)) + C1 + // and (X <s 0) ? C2 : C1 --> ((X >>s 31) & (C2 - C1)) + C1 + // FIXME: Type and constness constraints could be lifted, but we have to + // watch code size carefully. We should consider xor instead of + // sub/add when we decide to do that. + if (const IntegerType *Ty = dyn_cast<IntegerType>(CmpLHS->getType())) { + if (TrueVal->getType() == Ty) { + if (ConstantInt *Cmp = dyn_cast<ConstantInt>(CmpRHS)) { + ConstantInt *C1 = NULL, *C2 = NULL; + if (Pred == ICmpInst::ICMP_SGT && Cmp->isAllOnesValue()) { + C1 = dyn_cast<ConstantInt>(TrueVal); + C2 = dyn_cast<ConstantInt>(FalseVal); + } else if (Pred == ICmpInst::ICMP_SLT && Cmp->isNullValue()) { + C1 = dyn_cast<ConstantInt>(FalseVal); + C2 = dyn_cast<ConstantInt>(TrueVal); + } + if (C1 && C2) { + // This shift results in either -1 or 0. + Value *AShr = Builder->CreateAShr(CmpLHS, Ty->getBitWidth()-1); + + // Check if we can express the operation with a single or. + if (C2->isAllOnesValue()) + return ReplaceInstUsesWith(SI, Builder->CreateOr(AShr, C1)); + + Value *And = Builder->CreateAnd(AShr, C2->getValue()-C1->getValue()); + return ReplaceInstUsesWith(SI, Builder->CreateAdd(And, C1)); + } + } + } + } + if (CmpLHS == TrueVal && CmpRHS == FalseVal) { // Transform (X == Y) ? X : Y -> Y if (Pred == ICmpInst::ICMP_EQ) |
