[llvm-commits] [llvm] r94941 - in /llvm/trunk: lib/Transforms/InstCombine/InstCombineAddSub.cpp test/Transforms/InstCombine/sub.ll

[Eli Friedman]

Author: efriedma
Date: Sat Jan 30 20:30:23 2010
New Revision: 94941

URL: http://llvm.org/viewvc/llvm-project?rev=94941&view=rev
Log:
Add a small transform: transform -(X<<Y) to (-X<<Y) when the shift has a single
use and X is free to negate.


Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp
    llvm/trunk/test/Transforms/InstCombine/sub.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp?rev=94941&r1=94940&r2=94941&view=diff

==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp Sat Jan 30 20:30:23 2010
@@ -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) {

Modified: llvm/trunk/test/Transforms/InstCombine/sub.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/sub.ll?rev=94941&r1=94940&r2=94941&view=diff

==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/sub.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/sub.ll Sat Jan 30 20:30:23 2010
@@ -272,4 +272,12 @@
 ; CHECK-NEXT: ret i64 
 }
 
+define i32 @test26(i32 %x) {
+  %shl = shl i32 3, %x
+  %neg = sub i32 0, %shl
+  ret i32 %neg
+; CHECK: @test26
+; CHECK-NEXT: shl i32 -3
+; CHECK-NEXT: ret i32
+}