Make legalize a bit more efficient, and canonicalize sub X, C -> add X, -C

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@21882 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 5 insertions, 2 deletions

diff --git a/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index 08e8d776fd..8c26c5821b 100644
--- a/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -323,8 +323,11 @@ SDOperand SelectionDAGLegalize::LegalizeOp(SDOperand Op) {
     Tmp1 = LegalizeOp(Node->getOperand(0));  // Legalize the chain.
     // There is no need to legalize the size argument (Operand #1)
     if (Tmp1 != Node->getOperand(0))
-      Result = DAG.getNode(Node->getOpcode(), MVT::Other, Tmp1,
-                           Node->getOperand(1));
+      Node->setAdjCallChain(Tmp1);
+    // Note that we do not create new ADJCALLSTACK DOWN/UP nodes here.  These
+    // nodes are treated specially and are mutated in place.  This makes the dag
+    // legalization process more efficient and also makes libcall insertion
+    // easier.
     break;
   case ISD::DYNAMIC_STACKALLOC:
     Tmp1 = LegalizeOp(Node->getOperand(0));  // Legalize the chain.