[llvm-commits] CVS: llvm/lib/Transforms/Scalar/InstructionCombining.cpp

[Chris Lattner]

Changes in directory llvm/lib/Transforms/Scalar:

InstructionCombining.cpp updated: 1.723 -> 1.724
---
Log message:

Fix PR1253: http://llvm.org/PR1253  and xor2.ll:test[01]



---
Diffs of the changes:  (+30 -1)

 InstructionCombining.cpp |   31 ++++++++++++++++++++++++++++++-
 1 files changed, 30 insertions(+), 1 deletion(-)


Index: llvm/lib/Transforms/Scalar/InstructionCombining.cpp
diff -u llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.723 llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.724
--- llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.723	Mon Apr  2 08:45:30 2007
+++ llvm/lib/Transforms/Scalar/InstructionCombining.cpp	Mon Apr  2 20:47:41 2007
@@ -4714,7 +4714,36 @@
     // instruction can be folded into the icmp 
     if (Instruction *LHSI = dyn_cast<Instruction>(Op0))
       switch (LHSI->getOpcode()) {
-      case Instruction::And:
+      case Instruction::Xor:         // (icmp pred (and X, XorCST), CI)
+        if (ConstantInt *XorCST = dyn_cast<ConstantInt>(LHSI->getOperand(1))) {
+          // If this is a comparison that tests the signbit (X < 0) or (x > -1),
+          // fold the xor.
+          if (I.getPredicate() == ICmpInst::ICMP_SLT && CI->isZero() ||
+              I.getPredicate() == ICmpInst::ICMP_SGT && CI->isAllOnesValue()) {
+            Value *CompareVal = LHSI->getOperand(0);
+            
+            // If the sign bit of the XorCST is not set, there is no change to
+            // the operation, just stop using the Xor.
+            if (!XorCST->getValue().isNegative()) {
+              I.setOperand(0, CompareVal);
+              AddToWorkList(LHSI);
+              return &I;
+            }
+            
+            // Was the old condition true if the operand is positive?
+            bool isTrueIfPositive = I.getPredicate() == ICmpInst::ICMP_SGT;
+            
+            // If so, the new one isn't.
+            isTrueIfPositive ^= true;
+            
+            if (isTrueIfPositive)
+              return new ICmpInst(ICmpInst::ICMP_SGT, CompareVal, SubOne(CI));
+            else
+              return new ICmpInst(ICmpInst::ICMP_SLT, CompareVal, AddOne(CI));
+          }
+        }
+        break;
+      case Instruction::And:         // (icmp pred (and X, AndCST), CI)
         if (LHSI->hasOneUse() && isa<ConstantInt>(LHSI->getOperand(1)) &&
             LHSI->getOperand(0)->hasOneUse()) {
           ConstantInt *AndCST = cast<ConstantInt>(LHSI->getOperand(1));