From 9808f11b094a0b3a059e12cbe14ab627da7eecd4 Mon Sep 17 00:00:00 2001
From: David Majnemer <david.majnemer@gmail.com>
Date: Mon, 3 Nov 2014 05:53:55 +0000
Subject: [PATCH] InstCombine: Combine (X | Y) - X to (~X & Y)

This implements the transformation from (X | Y) - X to (~X & Y).

Differential Revision: http://reviews.llvm.org/D5791

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221129 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../InstCombine/InstCombineAddSub.cpp         | 21 +++++++++++++------
 test/Transforms/InstCombine/sub.ll            | 10 +++++++++
 2 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index ef6875238dd..902b640daca 100644
--- a/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1431,11 +1431,11 @@ Instruction *InstCombiner::visitFAdd(BinaryOperator &I) {
             Z2 = dyn_cast<Constant>(B2); B = B1;
         } else if (match(B1, m_AnyZero()) && match(A2, m_AnyZero())) {
             Z1 = dyn_cast<Constant>(B1); B = B2;
-            Z2 = dyn_cast<Constant>(A2); A = A1; 
+            Z2 = dyn_cast<Constant>(A2); A = A1;
         }
-        
-        if (Z1 && Z2 && 
-            (I.hasNoSignedZeros() || 
+
+        if (Z1 && Z2 &&
+            (I.hasNoSignedZeros() ||
              (Z1->isNegativeZeroValue() && Z2->isNegativeZeroValue()))) {
           return SelectInst::Create(C, A, B);
         }
@@ -1594,7 +1594,7 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
     // -(X >>u 31) -> (X >>s 31)
     // -(X >>s 31) -> (X >>u 31)
     if (C->isZero()) {
-      Value *X; 
+      Value *X;
       ConstantInt *CI;
       if (match(Op1, m_LShr(m_Value(X), m_ConstantInt(CI))) &&
           // Verify we are shifting out everything but the sign bit.
@@ -1609,7 +1609,7 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
   }
 
 
-  { 
+  {
     Value *Y;
     // X-(X+Y) == -Y    X-(Y+X) == -Y
     if (match(Op1, m_Add(m_Specific(Op0), m_Value(Y))) ||
@@ -1630,6 +1630,15 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
       return BinaryOperator::CreateAnd(A, B);
   }
 
+  if (Op0->hasOneUse()) {
+    Value *Y = nullptr;
+    // ((X | Y) - X) --> (~X & Y)
+    if (match(Op0, m_Or(m_Value(Y), m_Specific(Op1))) ||
+        match(Op0, m_Or(m_Specific(Op1), m_Value(Y))))
+      return BinaryOperator::CreateAnd(
+          Y, Builder->CreateNot(Op1, Op1->getName() + ".not"));
+  }
+
   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 95a61b1747c..0e421f75f13 100644
--- a/test/Transforms/InstCombine/sub.ll
+++ b/test/Transforms/InstCombine/sub.ll
@@ -540,3 +540,13 @@ define i32 @test45(i32 %x, i32 %y) {
 ; CHECK-NEXT: %sub = and i32 %x, %y
 ; CHECK: ret i32 %sub
 }
+
+define i32 @test46(i32 %x, i32 %y) {
+ %or = or i32 %x, %y
+ %sub = sub i32 %or, %x
+ ret i32 %sub
+; CHECK-LABEL: @test46(
+; CHECK-NEXT: %x.not = xor i32 %x, -1
+; CHECK-NEXT: %sub = and i32 %y, %x.not
+; CHECK: ret i32 %sub
+}
-- 
2.34.1