commit 7466678003f38f985d5b2dffd0917643137b11cf
author Benjamin Kramer <benny.kra@googlemail.com> Sat Feb 26 22:48:07 2011 +0000
committer Benjamin Kramer <benny.kra@googlemail.com> Sat Feb 26 22:48:07 2011 +0000
tree 8a0315a7b150080615e132dfa9cfc54c82fa42b1
parent 981b1c4c62054e4e39570a9230c0318f13f9a0a9

Add some DAGCombines for (adde 0, 0, glue), which are useful to optimize legalized code for large integer arithmetic.

1. Inform users of ADDEs with two 0 operands that it never sets carry
2. Fold other ADDs or ADDCs into the ADDE if possible

It would be neat if we could do the same thing for SETCC+ADD eventually, but we can't do that in target independent code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126557 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 9cc70a3..943731f 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -1290,6 +1290,16 @@
   return SDValue();
 }
 
+/// isCarryMaterialization - Returns true if V is an ADDE node that is known to
+/// return 0 or 1 depending on the carry flag.
+static bool isCarryMaterialization(SDValue V) {
+  if (V.getOpcode() != ISD::ADDE)
+    return false;
+
+  ConstantSDNode *C = dyn_cast<ConstantSDNode>(V.getOperand(0));
+  return C && C->isNullValue() && V.getOperand(0) == V.getOperand(1);
+}
+
 SDValue DAGCombiner::visitADD(SDNode *N) {
   SDValue N0 = N->getOperand(0);
   SDValue N1 = N->getOperand(1);
@@ -1453,6 +1463,18 @@
     return DAG.getNode(ISD::SUB, DL, VT, N1, ZExt);
   }
 
+  // add (adde 0, 0, glue), X -> adde X, 0, glue
+  if (N0->hasOneUse() && isCarryMaterialization(N0))
+    return DAG.getNode(ISD::ADDE, N->getDebugLoc(),
+                       DAG.getVTList(VT, MVT::Glue), N1, N0.getOperand(0),
+                       N0.getOperand(2));
+
+  // add X, (adde 0, 0, glue) -> adde X, 0, glue
+  if (N1->hasOneUse() && isCarryMaterialization(N1))
+    return DAG.getNode(ISD::ADDE, N->getDebugLoc(),
+                       DAG.getVTList(VT, MVT::Glue), N0, N1.getOperand(0),
+                       N1.getOperand(2));
+
   return SDValue();
 }
 
@@ -1496,6 +1518,16 @@
                                    N->getDebugLoc(), MVT::Glue));
   }
 
+  // addc (adde 0, 0, glue), X -> adde X, 0, glue
+  if (N0->hasOneUse() && isCarryMaterialization(N0))
+    return DAG.getNode(ISD::ADDE, N->getDebugLoc(), N->getVTList(), N1,
+                       DAG.getConstant(0, VT), N0.getOperand(2));
+
+  // addc X, (adde 0, 0, glue) -> adde X, 0, glue
+  if (N1->hasOneUse() && isCarryMaterialization(N1))
+    return DAG.getNode(ISD::ADDE, N->getDebugLoc(), N->getVTList(), N0,
+                       DAG.getConstant(0, VT), N1.getOperand(2));
+
   return SDValue();
 }
 
@@ -1506,6 +1538,12 @@
   ConstantSDNode *N0C = dyn_cast<ConstantSDNode>(N0);
   ConstantSDNode *N1C = dyn_cast<ConstantSDNode>(N1);
 
+  // If both operands are null we know that carry out will always be false.
+  if (N0C && N0C->isNullValue() && N0 == N1)
+    DAG.ReplaceAllUsesOfValueWith(SDValue(N, 1), DAG.getNode(ISD::CARRY_FALSE,
+                                                             N->getDebugLoc(),
+                                                             MVT::Glue));
+
   // canonicalize constant to RHS
   if (N0C && !N1C)
     return DAG.getNode(ISD::ADDE, N->getDebugLoc(), N->getVTList(),