From 29cd7db31097a1ae70a88d7f721a46f207363b46 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Fri, 31 Mar 2006 18:10:41 +0000
Subject: [PATCH] Remove dead *extloads.  This allows us to codegen
 vector.ll:test_extract_elt to:

test_extract_elt:
        alloc r3 = ar.pfs,0,1,0,0
        adds r8 = 12, r32
        ;;
        ldfs f8 = [r8]
        mov ar.pfs = r3
        br.ret.sptk.many rp

instead of:

test_extract_elt:
        alloc r3 = ar.pfs,0,1,0,0
        adds r8 = 28, r32
        adds r9 = 24, r32
        adds r10 = 20, r32
        adds r11 = 16, r32
        ;;
        ldfs f6 = [r8]
        ;;
        ldfs f6 = [r9]
        adds r8 = 12, r32
        adds r9 = 8, r32
        adds r14 = 4, r32
        ;;
        ldfs f6 = [r10]
        ;;
        ldfs f6 = [r11]
        ldfs f8 = [r8]
        ;;
        ldfs f6 = [r9]
        ;;
        ldfs f6 = [r14]
        ;;
        ldfs f6 = [r32]
        mov ar.pfs = r3
        br.ret.sptk.many rp


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@27297 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 4d1e39359ba..7eeb1003599 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -208,6 +208,7 @@ namespace {
     SDOperand visitBRCOND(SDNode *N);
     SDOperand visitBR_CC(SDNode *N);
     SDOperand visitLOAD(SDNode *N);
+    SDOperand visitXEXTLOAD(SDNode *N);
     SDOperand visitSTORE(SDNode *N);
     SDOperand visitINSERT_VECTOR_ELT(SDNode *N);
     SDOperand visitVINSERT_VECTOR_ELT(SDNode *N);
@@ -643,6 +644,9 @@ SDOperand DAGCombiner::visit(SDNode *N) {
   case ISD::BRCOND:             return visitBRCOND(N);
   case ISD::BR_CC:              return visitBR_CC(N);
   case ISD::LOAD:               return visitLOAD(N);
+  case ISD::EXTLOAD:
+  case ISD::SEXTLOAD:
+  case ISD::ZEXTLOAD:           return visitXEXTLOAD(N);
   case ISD::STORE:              return visitSTORE(N);
   case ISD::INSERT_VECTOR_ELT:  return visitINSERT_VECTOR_ELT(N);
   case ISD::VINSERT_VECTOR_ELT: return visitVINSERT_VECTOR_ELT(N);
@@ -2278,6 +2282,21 @@ SDOperand DAGCombiner::visitLOAD(SDNode *N) {
   return SDOperand();
 }
 
+/// visitXEXTLOAD - Handle EXTLOAD/ZEXTLOAD/SEXTLOAD.
+SDOperand DAGCombiner::visitXEXTLOAD(SDNode *N) {
+  SDOperand Chain    = N->getOperand(0);
+  SDOperand Ptr      = N->getOperand(1);
+  SDOperand SrcValue = N->getOperand(2);
+  SDOperand EVT      = N->getOperand(3);
+  
+  // 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);
+  
+  return SDOperand();
+}
+
 SDOperand DAGCombiner::visitSTORE(SDNode *N) {
   SDOperand Chain    = N->getOperand(0);
   SDOperand Value    = N->getOperand(1);