[llvm-commits] [llvm] r126151 - in /llvm/trunk/lib/CodeGen: RegAllocGreedy.cpp SplitKit.cpp SplitKit.h

[Jakob Stoklund Olesen]

Author: stoklund
Date: Mon Feb 21 17:09:46 2011
New Revision: 126151

URL: http://llvm.org/viewvc/llvm-project?rev=126151&view=rev
Log:
Add SplitKit::isOriginalEndpoint and use it to force live range splitting to terminate.

An original endpoint is an instruction that killed or defined the original live
range before any live ranges were split.

When splitting global live ranges, avoid creating local live ranges without any
original endpoints. We may still create global live ranges without original
endpoints, but such a range won't be split again, and live range splitting still
terminates.

Modified:
    llvm/trunk/lib/CodeGen/RegAllocGreedy.cpp
    llvm/trunk/lib/CodeGen/SplitKit.cpp
    llvm/trunk/lib/CodeGen/SplitKit.h

Modified: llvm/trunk/lib/CodeGen/RegAllocGreedy.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/RegAllocGreedy.cpp?rev=126151&r1=126150&r2=126151&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/RegAllocGreedy.cpp (original)
+++ llvm/trunk/lib/CodeGen/RegAllocGreedy.cpp Mon Feb 21 17:09:46 2011
@@ -426,8 +426,13 @@
         if (!IntI.valid())
           break;
         // Not live in, but before the first use.
-        if (IntI.start() < BI.FirstUse)
+        if (IntI.start() < BI.FirstUse) {
           BC.Entry = SpillPlacement::PrefSpill;
+          // If the block contains a kill from an earlier split, never split
+          // again in the same block.
+          if (!BI.LiveThrough && !SA->isOriginalEndpoint(BI.Kill))
+            BC.Entry = SpillPlacement::MustSpill;
+        }
       }
 
       // Does interference overlap the uses in the entry segment
@@ -458,8 +463,12 @@
           IntI.advanceTo(BI.LastUse);
           if (!IntI.valid())
             break;
-          if (IntI.start() < Stop)
+          if (IntI.start() < Stop) {
             BC.Exit = SpillPlacement::PrefSpill;
+            // Avoid splitting twice in the same block.
+            if (!BI.LiveThrough && !SA->isOriginalEndpoint(BI.Def))
+              BC.Exit = SpillPlacement::MustSpill;
+          }
         }
       }
     }

Modified: llvm/trunk/lib/CodeGen/SplitKit.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SplitKit.cpp?rev=126151&r1=126150&r2=126151&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SplitKit.cpp (original)
+++ llvm/trunk/lib/CodeGen/SplitKit.cpp Mon Feb 21 17:09:46 2011
@@ -167,6 +167,20 @@
   }
 }
 
+bool SplitAnalysis::isOriginalEndpoint(SlotIndex Idx) const {
+  unsigned OrigReg = VRM.getOriginal(CurLI->reg);
+  const LiveInterval &Orig = LIS.getInterval(OrigReg);
+  assert(!Orig.empty() && "Splitting empty interval?");
+  LiveInterval::const_iterator I = Orig.find(Idx);
+
+  // Range containing Idx should begin at Idx.
+  if (I != Orig.end() && I->start <= Idx)
+    return I->start == Idx;
+
+  // Range does not contain Idx, previous must end at Idx.
+  return I != Orig.begin() && (--I)->end == Idx;
+}
+
 void SplitAnalysis::print(const BlockPtrSet &B, raw_ostream &OS) const {
   for (BlockPtrSet::const_iterator I = B.begin(), E = B.end(); I != E; ++I) {
     unsigned count = UsingBlocks.lookup(*I);

Modified: llvm/trunk/lib/CodeGen/SplitKit.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SplitKit.h?rev=126151&r1=126150&r2=126151&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SplitKit.h (original)
+++ llvm/trunk/lib/CodeGen/SplitKit.h Mon Feb 21 17:09:46 2011
@@ -125,6 +125,13 @@
     return UsingBlocks.lookup(MBB);
   }
 
+  /// isOriginalEndpoint - Return true if the original live range was killed or
+  /// (re-)defined at Idx. Idx should be the 'def' slot for a normal kill/def,
+  /// and 'use' for an early-clobber def.
+  /// This can be used to recognize code inserted by earlier live range
+  /// splitting.
+  bool isOriginalEndpoint(SlotIndex Idx) const;
+
   typedef SmallPtrSet<const MachineBasicBlock*, 16> BlockPtrSet;
 
   // Print a set of blocks with use counts.