Add a small transform: transform -(X<<Y) to (-X<<Y) when the shift has a single
use and X is free to negate.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94941 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 4891ff0..119b1ca 100644
--- a/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -676,6 +676,13 @@
return BinaryOperator::CreateSDiv(Op1I->getOperand(0),
ConstantExpr::getNeg(DivRHS));
+ // 0 - (C << X) -> (-C << X)
+ if (Op1I->getOpcode() == Instruction::Shl)
+ if (ConstantInt *CSI = dyn_cast<ConstantInt>(Op0))
+ if (CSI->isZero())
+ if (Value *ShlLHSNeg = dyn_castNegVal(Op1I->getOperand(0)))
+ return BinaryOperator::CreateShl(ShlLHSNeg, Op1I->getOperand(1));
+
// X - X*C --> X * (1-C)
ConstantInt *C2 = 0;
if (dyn_castFoldableMul(Op1I, C2) == Op0) {