From fd27f8a5b38e8a2771db58b8b52843d13bc0cef0 Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Sun, 11 Oct 2009 21:29:45 +0000 Subject: [PATCH] generalize a transformation even more: we don't care whether the input the the mul is a zext from bool, just that it is all zeros other than the low bit. This fixes some phase ordering issues that would cause us to miss some xforms in mul.ll when the worklist is visited differently. llvm-svn: 83794 --- .../Scalar/InstructionCombining.cpp | 22 +++++++++---------- llvm/test/Transforms/InstCombine/mul.ll | 7 ++++++ 2 files changed, 17 insertions(+), 12 deletions(-) diff --git a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp index e9ffb7303055..549c57633a43 100644 --- a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp @@ -2781,20 +2781,18 @@ Instruction *InstCombiner::visitMul(BinaryOperator &I) { // If one of the operands of the multiply is a cast from a boolean value, then // we know the bool is either zero or one, so this is a 'masking' multiply. - // See if we can simplify things based on how the boolean was originally - // formed. - { - Value *BoolCast = 0, *OtherOp = 0; - if (ZExtInst *CI = dyn_cast(Op0)) - if (CI->getOperand(0)->getType() == Type::getInt1Ty(*Context)) - BoolCast = CI, OtherOp = I.getOperand(1); - if (!BoolCast) - if (ZExtInst *CI = dyn_cast(I.getOperand(1))) - if (CI->getOperand(0)->getType() == Type::getInt1Ty(*Context)) - BoolCast = CI, OtherOp = Op0; + // X * Y (where Y is 0 or 1) -> X & (0-Y) + if (!isa(I.getType())) { + // -2 is "-1 << 1" so it is all bits set except the low one. + APInt Negative2(I.getType()->getPrimitiveSizeInBits(), -2, true); + Value *BoolCast = 0, *OtherOp = 0; + if (MaskedValueIsZero(Op0, Negative2)) + BoolCast = Op0, OtherOp = I.getOperand(1); + else if (MaskedValueIsZero(I.getOperand(1), Negative2)) + BoolCast = I.getOperand(1), OtherOp = Op0; + if (BoolCast) { - // X * Y (where Y is 0 or 1) -> X & (0-Y) Value *V = Builder->CreateSub(Constant::getNullValue(I.getType()), BoolCast, "tmp"); return BinaryOperator::CreateAnd(V, OtherOp); diff --git a/llvm/test/Transforms/InstCombine/mul.ll b/llvm/test/Transforms/InstCombine/mul.ll index d8e623c48346..53a56434aede 100644 --- a/llvm/test/Transforms/InstCombine/mul.ll +++ b/llvm/test/Transforms/InstCombine/mul.ll @@ -105,5 +105,12 @@ define i32 @test16(i32 %b, i1 %c) { ret i32 %e } +; X * Y (when Y is 0 or 1) --> x & (0-Y) +define i32 @test17(i32 %a, i32 %b) { + %a.lobit = lshr i32 %a, 31 + %e = mul i32 %a.lobit, %b + ret i32 %e +} +