From 85958b059dcc4c1e91bb892d6cfe5987109a60ac Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Sun, 20 Sep 2009 07:21:39 +0000
Subject: [PATCH] Fold 'icmp eq (icmp), true' into an xor(icmp).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@82386 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/VMCore/ConstantFold.cpp                        | 14 ++++++++++++++
 .../ConstProp/2009-09-19-ConstFold-i1-ConstExpr.ll |  9 +++++++++
 2 files changed, 23 insertions(+)

diff --git a/lib/VMCore/ConstantFold.cpp b/lib/VMCore/ConstantFold.cpp
index e14dd7e9cff..d9ef2c95e76 100644
--- a/lib/VMCore/ConstantFold.cpp
+++ b/lib/VMCore/ConstantFold.cpp
@@ -1428,6 +1428,20 @@ Constant *llvm::ConstantFoldCompareInstruction(LLVMContext &Context,
       }
   }
 
+  // If the comparison is a comparison between two i1's, simplify it.
+  if (C1->getType() == Type::getInt1Ty(Context)) {
+    switch(pred) {
+    case ICmpInst::ICMP_EQ:
+      if (isa<ConstantInt>(C2))
+        return ConstantExpr::getXor(C1, ConstantExpr::getNot(C2));
+      return ConstantExpr::getXor(ConstantExpr::getNot(C1), C2);
+    case ICmpInst::ICMP_NE:
+      return ConstantExpr::getXor(C1, C2);
+    default:
+      break;
+    }
+  }
+
   if (isa<ConstantInt>(C1) && isa<ConstantInt>(C2)) {
     APInt V1 = cast<ConstantInt>(C1)->getValue();
     APInt V2 = cast<ConstantInt>(C2)->getValue();
diff --git a/test/Transforms/ConstProp/2009-09-19-ConstFold-i1-ConstExpr.ll b/test/Transforms/ConstProp/2009-09-19-ConstFold-i1-ConstExpr.ll
index 2dab2939d54..4cf13209739 100644
--- a/test/Transforms/ConstProp/2009-09-19-ConstFold-i1-ConstExpr.ll
+++ b/test/Transforms/ConstProp/2009-09-19-ConstFold-i1-ConstExpr.ll
@@ -27,3 +27,12 @@
 ; CHECK: @I = global i1 icmp ult (i8* @X, i8* @Y) ; <i1*> [#uses=0]
 @J = global i1 xor (i1 icmp ult (i8* @X, i8* @Y), i1 true)
 ; CHECK: @J = global i1 icmp uge (i8* @X, i8* @Y) ; <i1*> [#uses=0]
+
+@K = global i1 icmp eq (i1 icmp ult (i8* @X, i8* @Y), i1 false)
+; CHECK: @K = global i1 icmp uge (i8* @X, i8* @Y) ; <i1*> [#uses=0]
+@L = global i1 icmp eq (i1 icmp ult (i8* @X, i8* @Y), i1 true)
+; CHECK: @L = global i1 icmp ult (i8* @X, i8* @Y) ; <i1*> [#uses=0]
+@M = global i1 icmp ne (i1 icmp ult (i8* @X, i8* @Y), i1 true)
+; CHECK: @M = global i1 icmp uge (i8* @X, i8* @Y) ; <i1*> [#uses=0]
+@N = global i1 icmp ne (i1 icmp ult (i8* @X, i8* @Y), i1 false)
+; CHECK: @N = global i1 icmp ult (i8* @X, i8* @Y) ; <i1*> [#uses=0]
-- 
2.34.1