[llvm-commits] [llvm] r127347 - /llvm/trunk/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp

[Andrew Trick]

Author: atrick
Date: Wed Mar  9 13:12:43 2011
New Revision: 127347

URL: http://llvm.org/viewvc/llvm-project?rev=127347&view=rev
Log:
Improve pre-RA-sched register pressure tracking for duplicate operands.
This helps cases like 2008-07-19-movups-spills.ll, but doesn't have an obvious impact on benchmarks

Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp?rev=127347&r1=127346&r2=127347&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp Wed Mar  9 13:12:43 2011
@@ -419,11 +419,15 @@
           ST.adjustSchedDependency(OpSU, SU, const_cast<SDep &>(dep));
         }
 
-        if (!SU->addPred(dep) && !dep.isCtrl() && OpSU->NumRegDefsLeft > 0) {
+        if (!SU->addPred(dep) && !dep.isCtrl() && OpSU->NumRegDefsLeft > 1) {
           // Multiple register uses are combined in the same SUnit. For example,
           // we could have a set of glued nodes with all their defs consumed by
           // another set of glued nodes. Register pressure tracking sees this as
           // a single use, so to keep pressure balanced we reduce the defs.
+          //
+          // We can't tell (without more book-keeping) if this results from
+          // glued nodes or duplicate operands. As long as we don't reduce
+          // NumRegDefsLeft to zero, we handle the common cases well.
           --OpSU->NumRegDefsLeft;
         }
       }