From eabfa4787a23b3dc88d8a0022b334501bbc66d17 Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Fri, 6 May 2005 04:53:20 +0000 Subject: [PATCH] Teach instcombine propagate zeroness through shl instructions, implementing and.ll:test31 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@21717 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/Scalar/InstructionCombining.cpp | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-) diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp index 6cc7bbe3dc7..51141162bfb 100644 --- a/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/lib/Transforms/Scalar/InstructionCombining.cpp @@ -1361,14 +1361,10 @@ static bool MaskedValueIsZero(Value *V, ConstantIntegral *Mask) { break; } case Instruction::Shl: - // (shl X, C1) & C2 == 0 iff (-1 << C1) & C2 == 0 - if (ConstantUInt *SA = dyn_cast(I->getOperand(1))) { - Constant *C1 = ConstantIntegral::getAllOnesValue(I->getType()); - C1 = ConstantExpr::getShl(C1, SA); - C1 = ConstantExpr::getAnd(C1, Mask); - if (C1->isNullValue()) - return true; - } + // (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0 + if (ConstantUInt *SA = dyn_cast(I->getOperand(1))) + return MaskedValueIsZero(I->getOperand(0), + cast(ConstantExpr::getUShr(Mask, SA))); break; case Instruction::Shr: // (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0