From 694488f4770468f03b974180631c0fbfa21b28cc Mon Sep 17 00:00:00 2001
From: Eli Friedman <eli.friedman@gmail.com>
Date: Sun, 31 Jan 2010 02:30:23 +0000
Subject: 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
---
 lib/Transforms/InstCombine/InstCombineAddSub.cpp | 7 +++++++
 1 file changed, 7 insertions(+)

(limited to 'lib/Transforms/InstCombine/InstCombineAddSub.cpp')

diff --git a/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 4891ff00e7..119b1cad63 100644
--- a/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -676,6 +676,13 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
               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) {
-- 
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