From 0fd4e2e5a1836e52e0851e0ebb811e301dfd807e Mon Sep 17 00:00:00 2001
From: David Majnemer <david.majnemer@gmail.com>
Date: Sun, 19 Oct 2014 08:32:32 +0000
Subject: [PATCH] InstCombine: (sub (or A B) (xor A B)) --> (and A B)

The following implements the transformation:
(sub (or A B) (xor A B)) --> (and A B).

Patch by Ankur Garg!

Differential Revision: http://reviews.llvm.org/D5719

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220163 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/InstCombine/InstCombineAddSub.cpp |  9 +++++++++
 test/Transforms/InstCombine/sub.ll               | 10 ++++++++++
 2 files changed, 19 insertions(+)

diff --git a/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index ace75978331..ef6875238dd 100644
--- a/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1621,6 +1621,15 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
       return BinaryOperator::CreateNeg(Y);
   }
 
+  // (sub (or A, B) (xor A, B)) --> (and A, B)
+  {
+    Value *A = nullptr, *B = nullptr;
+    if (match(Op1, m_Xor(m_Value(A), m_Value(B))) &&
+        (match(Op0, m_Or(m_Specific(A), m_Specific(B))) ||
+         match(Op0, m_Or(m_Specific(B), m_Specific(A)))))
+      return BinaryOperator::CreateAnd(A, B);
+  }
+
   if (Op1->hasOneUse()) {
     Value *X = nullptr, *Y = nullptr, *Z = nullptr;
     Constant *C = nullptr;
diff --git a/test/Transforms/InstCombine/sub.ll b/test/Transforms/InstCombine/sub.ll
index 1d1bedc0a7b..95a61b1747c 100644
--- a/test/Transforms/InstCombine/sub.ll
+++ b/test/Transforms/InstCombine/sub.ll
@@ -530,3 +530,13 @@ define i32 @test44(i32 %x) {
 ; CHECK-NEXT: [[ADD:%.*]] = add nsw i32 %x, -32768
 ; CHECK: ret i32 [[ADD]]
 }
+
+define i32 @test45(i32 %x, i32 %y) {
+  %or = or i32 %x, %y
+  %xor = xor i32 %x, %y
+  %sub = sub i32 %or, %xor
+  ret i32 %sub
+; CHECK-LABEL: @test45(
+; CHECK-NEXT: %sub = and i32 %x, %y
+; CHECK: ret i32 %sub
+}