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

1 files changed, 5 insertions, 0 deletions

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index a559d3e469..4d1e39359b 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.