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Force coallescing of live ranges that have a single definition, even if they

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interfere.  Because these intervals have a single definition, and one of them
is a copy instruction, they are always safe to merge even if their lifetimes
interfere.  This slightly reduces the amount of spill code, for example on
252.eon, from:

 12837 spiller               - Number of loads added
  7604 spiller               - Number of stores added
  5842 spiller               - Number of register spills
 18155 liveintervals         - Number of identity moves eliminated after coalescing

to:

  12754 spiller               - Number of loads added
   7585 spiller               - Number of stores added
   5803 spiller               - Number of register spills
  18262 liveintervals         - Number of identity moves eliminated after coalescing

The much much bigger win would be to merge intervals with multiple definitions
(aka phi nodes) but this is not that day.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@15124 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2004-07-23 05:26:05 +00:00
parent eed80e2375
commit fe1630b43e
3 changed files with 31 additions and 9 deletions
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include/llvm/CodeGen/LiveIntervalAnalysis.h
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@@ -36,6 +36,7 @@ namespace llvm {
float weight; // weight of this interval:
// (number of uses *10^loopDepth)
Ranges ranges; // the ranges in which this register is live
bool isDefinedOnce; // True if there is one def of this register
explicit LiveInterval(unsigned r);