[llvm-commits] [llvm] r58555 - in /llvm/trunk: lib/Transforms/Scalar/InstructionCombining.cpp test/Transforms/InstCombine/2008-11-01-SRemDemandedBits.ll

[Nick Lewycky]

Author: nicholas
Date: Sat Nov  1 21:41:50 2008
New Revision: 58555

URL: http://llvm.org/viewvc/llvm-project?rev=58555&view=rev
Log:
Fix demanded bits analysis with srem by negative number. Based on a patch
by Richard Osborne.

Added:
    llvm/trunk/test/Transforms/InstCombine/2008-11-01-SRemDemandedBits.ll
Modified:
    llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp?rev=58555&r1=58554&r2=58555&view=diff

==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp Sat Nov  1 21:41:50 2008
@@ -1274,12 +1274,12 @@
     break;
   case Instruction::SRem:
     if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
-      APInt RA = Rem->getValue();
-      if (RA.isPowerOf2() || (-RA).isPowerOf2()) {
+      APInt RA = Rem->getValue().abs();
+      if (RA.isPowerOf2()) {
         if (DemandedMask.ule(RA))    // srem won't affect demanded bits
           return UpdateValueUsesWith(I, I->getOperand(0));
 
-        APInt LowBits = RA.isStrictlyPositive() ? (RA - 1) : ~RA;
+        APInt LowBits = RA - 1;
         APInt Mask2 = LowBits | APInt::getSignBit(BitWidth);
         if (SimplifyDemandedBits(I->getOperand(0), Mask2,
                                  LHSKnownZero, LHSKnownOne, Depth+1))

Added: llvm/trunk/test/Transforms/InstCombine/2008-11-01-SRemDemandedBits.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/2008-11-01-SRemDemandedBits.ll?rev=58555&view=auto

==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/2008-11-01-SRemDemandedBits.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/2008-11-01-SRemDemandedBits.ll Sat Nov  1 21:41:50 2008
@@ -0,0 +1,8 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {ret i1 true}
+; PR2993
+
+define i1 @foo(i32 %x) {
+  %1 = srem i32 %x, -1
+  %2 = icmp eq i32 %1, 0
+  ret i1 %2
+}