From e4b953939c2848cd71ab4aeaecaa150ba1ae7fd9 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Fri, 31 Mar 2006 18:06:18 +0000
Subject: [PATCH] Delete dead loads in the dag.  This allows us to compile
 vector.ll:test_extract_elt2 into:

_test_extract_elt2:
        lfd f1, 32(r3)
        blr

instead of:

_test_extract_elt2:
        lfd f0, 56(r3)
        lfd f0, 48(r3)
        lfd f0, 40(r3)
        lfd f1, 32(r3)
        lfd f0, 24(r3)
        lfd f0, 16(r3)
        lfd f0, 8(r3)
        lfd f0, 0(r3)
        blr


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@27296 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index a559d3e469e..4d1e39359ba 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2261,6 +2261,11 @@ SDOperand DAGCombiner::visitLOAD(SDNode *N) {
   SDOperand Chain    = N->getOperand(0);
   SDOperand Ptr      = N->getOperand(1);
   SDOperand SrcValue = N->getOperand(2);
+
+  // If there are no uses of the loaded value, change uses of the chain value
+  // into uses of the chain input (i.e. delete the dead load).
+  if (N->hasNUsesOfValue(0, 0))
+    return CombineTo(N, DAG.getNode(ISD::UNDEF, N->getValueType(0)), Chain);
   
   // If this load is directly stored, replace the load value with the stored
   // value.