[llvm-commits] CVS: llvm/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp

[David Greene]

Changes in directory llvm/lib/CodeGen/SelectionDAG:

ScheduleDAGRRList.cpp updated: 1.31 -> 1.32
---
Log message:

Remove the "special tie breaker" because it resulted in inconsistent
ordering and thus violated the strict weak ordering requirement of
priority_queue.  Uncovered by _GLIBCXX_DEBUG.


---
Diffs of the changes:  (+12 -10)

 ScheduleDAGRRList.cpp |   22 ++++++++++++----------
 1 files changed, 12 insertions(+), 10 deletions(-)


Index: llvm/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
diff -u llvm/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp:1.31 llvm/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp:1.32
--- llvm/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp:1.31	Thu Jun 21 20:35:51 2007
+++ llvm/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp	Thu Jun 28 21:48:09 2007
@@ -618,16 +618,18 @@
   bool LIsTarget = left->Node->isTargetOpcode();
   bool RIsTarget = right->Node->isTargetOpcode();
 
-  // Special tie breaker: if two nodes share a operand, the one that use it
-  // as a def&use operand is preferred.
-  if (LIsTarget && RIsTarget) {
-    if (left->isTwoAddress && !right->isTwoAddress)
-      if (SPQ->isDUOperand(left, right))
-        return false;
-    if (!left->isTwoAddress && right->isTwoAddress)
-      if (SPQ->isDUOperand(right, left))
-        return true;
-  }
+  // Cray: There used to be a special tie breaker here that looked for
+  // two-address instructions and preferred the instruction with a
+  // def&use operand.  The special case triggered diagnostics when
+  // _GLIBCXX_DEBUG was enabled because it broke the strict weak
+  // ordering that priority_queue requires. It didn't help much anyway
+  // because AddPseudoTwoAddrDeps already covers many of the cases
+  // where it would have applied.  In addition, it's counter-intuitive
+  // that a tie breaker would be the first thing attempted.  There's a
+  // "real" tie breaker below that is the operation of last resort.
+  // The fact that the "special tie breaker" would trigger when there
+  // wasn't otherwise a tie is what broke the strict weak ordering
+  // constraint.
 
   unsigned LPriority = SPQ->getNodePriority(left);
   unsigned RPriority = SPQ->getNodePriority(right);