[llvm-commits] [llvm] r54906 - in /llvm/trunk: lib/Transforms/Scalar/InstructionCombining.cpp test/Transforms/InstCombine/2008-08-17-ICmpXorSignbit.ll

[Nick Lewycky]

Author: nicholas
Date: Sun Aug 17 14:58:24 2008
New Revision: 54906

URL: http://llvm.org/viewvc/llvm-project?rev=54906&view=rev
Log:
Consider the case where xor by -1 and xor by 128 have been combined already to
produce an xor by 127.

Modified:
    llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
    llvm/trunk/test/Transforms/InstCombine/2008-08-17-ICmpXorSignbit.ll

Modified: llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp?rev=54906&r1=54905&r2=54906&view=diff

==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp Sun Aug 17 14:58:24 2008
@@ -5503,8 +5503,8 @@
             return new ICmpInst(I.getPredicate(), Op0I->getOperand(0),
                                 Op1I->getOperand(0));
           } else {
-            // icmp u/s (a ^ signbit), (b ^ signbit) --> icmp s/u a, b
             if (ConstantInt *CI = dyn_cast<ConstantInt>(Op0I->getOperand(1))) {
+              // icmp u/s (a ^ signbit), (b ^ signbit) --> icmp s/u a, b
               if (CI->getValue().isSignBit()) {
                 ICmpInst::Predicate Pred = I.isSignedPredicate()
                                                ? I.getUnsignedPredicate()
@@ -5512,6 +5512,17 @@
                 return new ICmpInst(Pred, Op0I->getOperand(0),
                                     Op1I->getOperand(0));
               }
+
+              // icmp u/s (a ^ ~signbit), (b ^ ~signbit) --> icmp s/u b, a
+              if ((~CI->getValue()).isSignBit()) {
+                ICmpInst::Predicate Pred = I.isSignedPredicate()
+                                               ? I.getUnsignedPredicate()
+                                               : I.getSignedPredicate();
+                Pred = I.getSwappedPredicate(Pred);
+                return new ICmpInst(Pred, Op0I->getOperand(0),
+                                    Op1I->getOperand(0));
+
+              }
             }
           }
           break;
@@ -5818,6 +5829,17 @@
         return new ICmpInst(Pred, LHSI->getOperand(0),
                             ConstantInt::get(RHSV ^ SignBit));
       }
+
+      // (icmp u/s (xor A ~SignBit), C) -> (icmp ~s/u A, (xor C ~SignBit))
+      if (!ICI.isEquality() && (~XorCST->getValue()).isSignBit()) {
+        const APInt &NotSignBit = XorCST->getValue();
+        ICmpInst::Predicate Pred = ICI.isSignedPredicate()
+                                       ? ICI.getUnsignedPredicate()
+                                       : ICI.getSignedPredicate();
+        Pred = ICI.getSwappedPredicate(Pred);
+        return new ICmpInst(Pred, LHSI->getOperand(0),
+                            ConstantInt::get(RHSV ^ NotSignBit));
+      }
     }
     break;
   case Instruction::And:         // (icmp pred (and X, AndCST), RHS)

Modified: llvm/trunk/test/Transforms/InstCombine/2008-08-17-ICmpXorSignbit.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/2008-08-17-ICmpXorSignbit.ll?rev=54906&r1=54905&r2=54906&view=diff

==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/2008-08-17-ICmpXorSignbit.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/2008-08-17-ICmpXorSignbit.ll Sun Aug 17 14:58:24 2008
@@ -20,3 +20,22 @@
   ret i1 %tmp
 }
 
+define i1 @test4(i8 %x, i8 %y) {
+  %X = xor i8 %x, 127
+  %Y = xor i8 %y, 127
+  %tmp = icmp slt i8 %X, %Y
+  ret i1 %tmp
+}
+
+define i1 @test5(i8 %x, i8 %y) {
+  %X = xor i8 %x, 127
+  %Y = xor i8 %y, 127
+  %tmp = icmp ult i8 %X, %Y
+  ret i1 %tmp
+}
+
+define i1 @test6(i8 %x) {
+  %X = xor i8 %x, 127
+  %tmp = icmp uge i8 %X, 15
+  ret i1 %tmp
+}