From c6b8ba86738cb6187835e440f2baafaa24dea0b2 Mon Sep 17 00:00:00 2001
From: Eli Friedman <eli.friedman@gmail.com>
Date: Mon, 19 Sep 2011 21:58:15 +0000
Subject: [PATCH] Fix an infinite loop where a transform in
 InstCombiner::visitAnd claims a construct is changed when it is not.  (See
 included testcase.)

Patch by Xiaoyi Guo.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@140072 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../InstCombine/InstCombineAndOrXor.cpp       | 43 ++++++++++---------
 test/Transforms/InstCombine/and2.ll           |  7 +++
 2 files changed, 29 insertions(+), 21 deletions(-)

diff --git a/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 32920fabc3d..d16f8ce821d 100644
--- a/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -1174,30 +1174,31 @@ Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
         ((A == C && B == D) || (A == D && B == C)))
       return BinaryOperator::CreateXor(A, B);
     
-    if (Op0->hasOneUse() &&
-        match(Op0, m_Xor(m_Value(A), m_Value(B)))) {
-      if (A == Op1) {                                // (A^B)&A -> A&(A^B)
-        I.swapOperands();     // Simplify below
-        std::swap(Op0, Op1);
-      } else if (B == Op1) {                         // (A^B)&B -> B&(B^A)
-        cast<BinaryOperator>(Op0)->swapOperands();
-        I.swapOperands();     // Simplify below
-        std::swap(Op0, Op1);
+    // A&(A^B) => A & ~B
+    {
+      Value *tmpOp0 = Op0;
+      Value *tmpOp1 = Op1;
+      if (Op0->hasOneUse() &&
+          match(Op0, m_Xor(m_Value(A), m_Value(B)))) {
+        if (A == Op1 || B == Op1 ) {
+          tmpOp1 = Op0;
+          tmpOp0 = Op1;
+          // Simplify below
+        }
       }
-    }
 
-    if (Op1->hasOneUse() &&
-        match(Op1, m_Xor(m_Value(A), m_Value(B)))) {
-      if (B == Op0) {                                // B&(A^B) -> B&(B^A)
-        cast<BinaryOperator>(Op1)->swapOperands();
-        std::swap(A, B);
+      if (tmpOp1->hasOneUse() &&
+          match(tmpOp1, m_Xor(m_Value(A), m_Value(B)))) {
+        if (B == tmpOp0) {
+          std::swap(A, B);
+        }
+        // Notice that the patten (A&(~B)) is actually (A&(-1^B)), so if
+        // A is originally -1 (or a vector of -1 and undefs), then we enter
+        // an endless loop. By checking that A is non-constant we ensure that
+        // we will never get to the loop.
+        if (A == tmpOp0 && !isa<Constant>(A)) // A&(A^B) -> A & ~B
+          return BinaryOperator::CreateAnd(A, Builder->CreateNot(B, "tmp"));
       }
-      // Notice that the patten (A&(~B)) is actually (A&(-1^B)), so if
-      // A is originally -1 (or a vector of -1 and undefs), then we enter
-      // an endless loop. By checking that A is non-constant we ensure that
-      // we will never get to the loop.
-      if (A == Op0 && !isa<Constant>(A)) // A&(A^B) -> A & ~B
-        return BinaryOperator::CreateAnd(A, Builder->CreateNot(B, "tmp"));
     }
 
     // (A&((~A)|B)) -> A&B
diff --git a/test/Transforms/InstCombine/and2.ll b/test/Transforms/InstCombine/and2.ll
index a8881522eac..531aedb668a 100644
--- a/test/Transforms/InstCombine/and2.ll
+++ b/test/Transforms/InstCombine/and2.ll
@@ -35,3 +35,10 @@ define i1 @test4(i32 %X) {
 ; CHECK: @test4
 ; CHECK-NEXT: ret i1 false
 }
+
+; Make sure we don't go into an infinite loop with this test
+define <4 x i32> @test5(<4 x i32> %A) {
+  %1 = xor <4 x i32> %A, <i32 1, i32 2, i32 3, i32 4>
+  %2 = and <4 x i32> <i32 1, i32 2, i32 3, i32 4>, %1
+  ret <4 x i32> %2
+}