diff options
| -rw-r--r-- | lib/Transforms/Scalar/InstructionCombining.cpp | 17 |
1 files changed, 17 insertions, 0 deletions
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp index fac659f39b..b12c6b5841 100644 --- a/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/lib/Transforms/Scalar/InstructionCombining.cpp @@ -6023,6 +6023,23 @@ Instruction *InstCombiner::visitTrunc(CastInst &CI) { Value *V = InsertCastBefore(SrcI->getOperand(0), Ty, CI); return new ShiftInst(Instruction::LShr, V, SrcI->getOperand(1)); } + } else { // This is a variable shr. + + // Turn 'trunc (lshr X, Y) to bool' into '(X & (1 << Y)) != 0'. This is + // more LLVM instructions, but allows '1 << Y' to be hoisted if + // loop-invariant and CSE'd. + if (CI.getType() == Type::BoolTy && SrcI->hasOneUse()) { + Value *One = ConstantInt::get(SrcI->getType(), 1); + + Value *V = InsertNewInstBefore(new ShiftInst(Instruction::Shl, One, + SrcI->getOperand(1), + "tmp"), CI); + V = InsertNewInstBefore(BinaryOperator::createAnd(V, + SrcI->getOperand(0), + "tmp"), CI); + Value *Zero = Constant::getNullValue(V->getType()); + return BinaryOperator::createSetNE(V, Zero); + } } break; } |