From 854077d3a5a42c3286f22fd5f72ee98797ed3d71 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Mon, 17 Oct 2005 01:07:11 +0000
Subject: add a trivial fold

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@23764 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 5b1d103..69478e3 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -532,6 +532,10 @@ SDOperand DAGCombiner::visitSUB(SDNode *N) {
   ConstantSDNode *N0C = dyn_cast<ConstantSDNode>(N0.Val);
   ConstantSDNode *N1C = dyn_cast<ConstantSDNode>(N1.Val);
   
+  // fold (sub x, x) -> 0
+  if (N0 == N1)
+    return DAG.getConstant(0, N->getValueType(0));
+  
   // fold (sub c1, c2) -> c1-c2
   if (N0C && N1C)
     return DAG.getConstant(N0C->getValue() - N1C->getValue(),
-- 
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