From 922d4ab57489bd1ae29cc7714ef496dbfef26cc7 Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Mon, 23 Nov 2009 03:17:33 +0000
Subject: [PATCH] Reapply r88830 with a bugfix: this transform only applies to
 icmp eq/ne. This fixes part of PR5438.

llvm-svn: 89639
---
 .../Scalar/InstructionCombining.cpp           | 30 +++++++++++++++++++
 .../Transforms/InstCombine/compare-signs.ll   |  1 -
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
index 6f74902e1b42..99555ea9b38b 100644
--- a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -8539,6 +8539,36 @@ Instruction *InstCombiner::transformZExtICmp(ICmpInst *ICI, Instruction &CI,
     }
   }
 
+  // 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;
 }
 
diff --git a/llvm/test/Transforms/InstCombine/compare-signs.ll b/llvm/test/Transforms/InstCombine/compare-signs.ll
index 2f98641a2494..ba638ba36fc0 100644
--- a/llvm/test/Transforms/InstCombine/compare-signs.ll
+++ b/llvm/test/Transforms/InstCombine/compare-signs.ll
@@ -1,5 +1,4 @@
 ; RUN: opt %s -instcombine -S | FileCheck %s
-; XFAIL: *
 ; PR5438
 
 ; TODO: This should also optimize down.