From d08831499818771527e2da55eedd0bdfbdc37edb Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Sun, 11 Oct 2009 22:22:13 +0000
Subject: [PATCH] teach instcombine to simplify xor's harder, catching the new
 testcase.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@83799 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../Scalar/InstructionCombining.cpp           | 27 +++++++++++++++++++
 test/Transforms/InstCombine/xor2.ll           | 11 ++++++++
 2 files changed, 38 insertions(+)

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 6d166664f8f..dcb65a8ed91 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -1047,6 +1047,33 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
     if (ShrinkDemandedConstant(I, 1, DemandedMask))
       return I;
     
+    // If our LHS is an 'and' and if it has one use, and if any of the bits we
+    // are flipping are known to be set, then the xor is just resetting those
+    // bits to zero.  We can just knock out bits from the 'and' and the 'xor',
+    // simplifying both of them.
+    if (Instruction *LHSInst = dyn_cast<Instruction>(I->getOperand(0)))
+      if (LHSInst->getOpcode() == Instruction::And && LHSInst->hasOneUse() &&
+          isa<ConstantInt>(I->getOperand(1)) &&
+          isa<ConstantInt>(LHSInst->getOperand(1)) &&
+          (LHSKnownOne & RHSKnownOne & DemandedMask) != 0) {
+        ConstantInt *AndRHS = cast<ConstantInt>(LHSInst->getOperand(1));
+        ConstantInt *XorRHS = cast<ConstantInt>(I->getOperand(1));
+        APInt NewMask = ~(LHSKnownOne & RHSKnownOne & DemandedMask);
+        
+        Constant *AndC =
+          ConstantInt::get(I->getType(), NewMask & AndRHS->getValue());
+        Instruction *NewAnd = 
+          BinaryOperator::CreateAnd(I->getOperand(0), AndC, "tmp");
+        InsertNewInstBefore(NewAnd, *I);
+        
+        Constant *XorC =
+          ConstantInt::get(I->getType(), NewMask & XorRHS->getValue());
+        Instruction *NewXor =
+          BinaryOperator::CreateXor(NewAnd, XorC, "tmp");
+        return InsertNewInstBefore(NewXor, *I);
+      }
+          
+          
     RHSKnownZero = KnownZeroOut;
     RHSKnownOne  = KnownOneOut;
     break;
diff --git a/test/Transforms/InstCombine/xor2.ll b/test/Transforms/InstCombine/xor2.ll
index 94a464c8dcd..23a99158137 100644
--- a/test/Transforms/InstCombine/xor2.ll
+++ b/test/Transforms/InstCombine/xor2.ll
@@ -30,3 +30,14 @@ define i32 @test2(i32 %tmp1) {
         %ov110 = xor i32 %ov3, 153
         ret i32 %ov110
 }
+
+define i32 @test3(i32 %tmp1) {
+; CHECK:      @test3
+; CHECK-NEXT:   or i32 %tmp1, 8 
+; CHECK-NEXT:   and i32
+; CHECK-NEXT:   ret i32
+  %ovm = or i32 %tmp1, 145 
+  %ov31 = and i32 %ovm, 177
+  %ov110 = xor i32 %ov31, 153
+  ret i32 %ov110
+}