Always normalize spill weights, also for intervals created by spilling.

Moderate the weight given to very small intervals.

The spill weight given to new intervals created when spilling was not
normalized in the same way as the original spill weights calculated by
CalcSpillWeights. That meant that restored registers would tend to hang around
because they had a much higher spill weight that unspilled registers.

This improves the runtime of a few tests by up to 10%, and there are no
significant regressions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@96613 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/CodeGen/LiveIntervalAnalysis.h b/include/llvm/CodeGen/LiveIntervalAnalysis.h
index d7ff8da02a51a498705731bd8007f888f908f4d4..294eb25fb23f8f9499e337adf19f1c6930f64d95 100644 (file)
--- a/include/llvm/CodeGen/LiveIntervalAnalysis.h
+++ b/include/llvm/CodeGen/LiveIntervalAnalysis.h
@@ -74,6 +74,14 @@ namespace llvm {
       return (isDef + isUse) * powf(10.0F, (float)loopDepth);
     }
 
+    // After summing the spill weights of all defs and uses, the final weight
+    // should be normalized, dividing the weight of the interval by its size.
+    // This encourages spilling of intervals that are large and have few uses,
+    // and discourages spilling of small intervals with many uses.
+    void normalizeSpillWeight(LiveInterval &li) {
+      li.weight /= getApproximateInstructionCount(li) + 25;
+    }
+
     typedef Reg2IntervalMap::iterator iterator;
     typedef Reg2IntervalMap::const_iterator const_iterator;
     const_iterator begin() const { return r2iMap_.begin(); }
@@ -409,6 +417,9 @@ namespace llvm {
         DenseMap<unsigned,unsigned> &MBBVRegsMap,
         std::vector<LiveInterval*> &NewLIs);
 
+    // Normalize the spill weight of all the intervals in NewLIs.
+    void normalizeSpillWeights(std::vector<LiveInterval*> &NewLIs);
+
     static LiveInterval* createInterval(unsigned Reg);
 
     void printInstrs(raw_ostream &O) const;

diff --git a/lib/CodeGen/CalcSpillWeights.cpp b/lib/CodeGen/CalcSpillWeights.cpp
index 2bedd0424345ec4e7df60b722f554aebf956d7ae..a328d0e556e91012cb479f063b2e671f7b1e0b51 100644 (file)
--- a/lib/CodeGen/CalcSpillWeights.cpp
+++ b/lib/CodeGen/CalcSpillWeights.cpp
@@ -131,10 +131,7 @@ bool CalculateSpillWeights::runOnMachineFunction(MachineFunction &fn) {
       if (Hint.first || Hint.second)
         li.weight *= 1.01F;
 
-      // Divide the weight of the interval by its size.  This encourages
-      // spilling of intervals that are large and have few uses, and
-      // discourages spilling of small intervals with many uses.
-      li.weight /= lis->getApproximateInstructionCount(li) * SlotIndex::NUM;
+      lis->normalizeSpillWeight(li);
     }
   }
   

diff --git a/lib/CodeGen/LiveIntervalAnalysis.cpp b/lib/CodeGen/LiveIntervalAnalysis.cpp
index f6bf43394032b751d025da9ad761da17594ef366..0b38ffb9703e95b39b8fc22702aabf192403a644 100644 (file)
--- a/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -1562,6 +1562,12 @@ LiveIntervals::handleSpilledImpDefs(const LiveInterval &li, VirtRegMap &vrm,
   }
 }
 
+void
+LiveIntervals::normalizeSpillWeights(std::vector<LiveInterval*> &NewLIs) {
+  for (unsigned i = 0, e = NewLIs.size(); i != e; ++i)
+    normalizeSpillWeight(*NewLIs[i]);
+}
+
 std::vector<LiveInterval*> LiveIntervals::
 addIntervalsForSpillsFast(const LiveInterval &li,
                           const MachineLoopInfo *loopInfo,
@@ -1739,6 +1745,7 @@ addIntervalsForSpills(const LiveInterval &li,
     }
 
     handleSpilledImpDefs(li, vrm, rc, NewLIs);
+    normalizeSpillWeights(NewLIs);
     return NewLIs;
   }
 
@@ -1814,6 +1821,7 @@ addIntervalsForSpills(const LiveInterval &li,
   // Insert spills / restores if we are splitting.
   if (!TrySplit) {
     handleSpilledImpDefs(li, vrm, rc, NewLIs);
+    normalizeSpillWeights(NewLIs);
     return NewLIs;
   }
 
@@ -1973,6 +1981,7 @@ addIntervalsForSpills(const LiveInterval &li,
   }
 
   handleSpilledImpDefs(li, vrm, rc, RetNewLIs);
+  normalizeSpillWeights(RetNewLIs);
   return RetNewLIs;
 }
 

diff --git a/test/CodeGen/X86/2008-02-22-ReMatBug.ll b/test/CodeGen/X86/2008-02-22-ReMatBug.ll
index 8d6bb0df1f6d07a64cd31460a1a8b7c6164d3db6..a91ac27f98ddd01c1e9eeac09b4d48d9fc83b8bf 100644 (file)
--- a/test/CodeGen/X86/2008-02-22-ReMatBug.ll
+++ b/test/CodeGen/X86/2008-02-22-ReMatBug.ll
@@ -1,4 +1,4 @@
-; RUN: llc < %s -march=x86 -stats |& grep {Number of re-materialization} | grep 3
+; RUN: llc < %s -march=x86 -stats |& grep {Number of re-materialization} | grep 2
 ; rdar://5761454
 
        %struct.quad_struct = type { i32, i32, %struct.quad_struct*, %struct.quad_struct*, %struct.quad_struct*, %struct.quad_struct*, %struct.quad_struct* }

diff --git a/test/CodeGen/X86/pr3495-2.ll b/test/CodeGen/X86/pr3495-2.ll
index 71aa5a04881e88f60a2e64c2d421ee10724defa4..98c064a07db926603efe90eebe0533424c75ef34 100644 (file)
--- a/test/CodeGen/X86/pr3495-2.ll
+++ b/test/CodeGen/X86/pr3495-2.ll
@@ -1,4 +1,8 @@
-; RUN: llc < %s -march=x86 -relocation-model=pic -disable-fp-elim -stats |& grep {Number of reloads omited}
+; RUN: llc < %s -march=x86 -relocation-model=pic -disable-fp-elim -stats |& grep {Number of loads added} | grep 1
+; PR3495
+;
+; This test may not be testing what it was supposed to test.
+; It used to have two spills and four reloads, but not it only has one spill and one reload.
 
 target datalayout = "e-p:32:32:32"
 target triple = "i386-apple-darwin9.6"