[llvm-commits] [llvm] r89639 - in /llvm/trunk: lib/Transforms/Scalar/InstructionCombining.cpp test/Transforms/InstCombine/compare-signs.ll

[Nick Lewycky]

Author: nicholas
Date: Sun Nov 22 21:17:33 2009
New Revision: 89639

URL: http://llvm.org/viewvc/llvm-project?rev=89639&view=rev
Log:
Reapply r88830 with a bugfix: this transform only applies to icmp eq/ne. This
fixes part of PR5438.

Modified:
    llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
    llvm/trunk/test/Transforms/InstCombine/compare-signs.ll

Modified: llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp?rev=89639&r1=89638&r2=89639&view=diff

==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp Sun Nov 22 21:17:33 2009
@@ -8539,6 +8539,36 @@
     }
   }
 
+  // icmp ne A, B is equal to xor A, B when A and B only really have one bit.
+  // It is also profitable to transform icmp eq into not(xor(A, B)) because that
+  // may lead to additional simplifications.
+  if (ICI->isEquality() && CI.getType() == ICI->getOperand(0)->getType()) {
+    if (const IntegerType *ITy = dyn_cast<IntegerType>(CI.getType())) {
+      uint32_t BitWidth = ITy->getBitWidth();
+      if (BitWidth > 1) {
+        Value *LHS = ICI->getOperand(0);
+        Value *RHS = ICI->getOperand(1);
+
+        APInt KnownZeroLHS(BitWidth, 0), KnownOneLHS(BitWidth, 0);
+        APInt KnownZeroRHS(BitWidth, 0), KnownOneRHS(BitWidth, 0);
+        APInt TypeMask(APInt::getHighBitsSet(BitWidth, BitWidth-1));
+        ComputeMaskedBits(LHS, TypeMask, KnownZeroLHS, KnownOneLHS);
+        ComputeMaskedBits(RHS, TypeMask, KnownZeroRHS, KnownOneRHS);
+
+        if (KnownZeroLHS.countLeadingOnes() == BitWidth-1 &&
+            KnownZeroRHS.countLeadingOnes() == BitWidth-1) {
+          if (!DoXform) return ICI;
+
+          Value *Xor = Builder->CreateXor(LHS, RHS);
+          if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
+            Xor = Builder->CreateXor(Xor, ConstantInt::get(ITy, 1));
+          Xor->takeName(ICI);
+          return ReplaceInstUsesWith(CI, Xor);
+        }
+      }
+    }
+  }
+
   return 0;
 }
 

Modified: llvm/trunk/test/Transforms/InstCombine/compare-signs.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/compare-signs.ll?rev=89639&r1=89638&r2=89639&view=diff

==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/compare-signs.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/compare-signs.ll Sun Nov 22 21:17:33 2009
@@ -1,5 +1,4 @@
 ; RUN: opt %s -instcombine -S | FileCheck %s
-; XFAIL: *
 ; PR5438
 
 ; TODO: This should also optimize down.