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Tweak cross-class coalescing to be more aggressive when the target class is small.

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The greedy register allocator has live range splitting and register class
inflation, so it can actually fully undo this join, including restoring the
original register classes.

We still don't want to do this for long live ranges, mostly because of the high
register pressure of there are many constrained live ranges overlapping.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@131466 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jakob Stoklund Olesen 2011-05-17 16:38:37 +00:00
parent ab078f0232
commit 6e3b3e2122
1 changed files with 9 additions and 3 deletions
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12
lib/CodeGen/SimpleRegisterCoalescing.cpp
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@ -987,8 +987,14 @@ SimpleRegisterCoalescing::isWinToJoinCrossClass(unsigned SrcReg,
LiveInterval &DstInt = li_->getInterval(DstReg);
unsigned SrcSize = li_->getApproximateInstructionCount(SrcInt);
unsigned DstSize = li_->getApproximateInstructionCount(DstInt);
if (SrcSize <= NewRCCount && DstSize <= NewRCCount)
// Coalesce aggressively if the intervals are small compared to the number of
// registers in the new class. The number 4 is fairly arbitrary, chosen to be
// less aggressive than the 8 used for the whole function size.
const unsigned ThresSize = 4 * NewRCCount;
if (SrcSize <= ThresSize && DstSize <= ThresSize)
return true;
// Estimate *register use density*. If it doubles or more, abort.
unsigned SrcUses = std::distance(mri_->use_nodbg_begin(SrcReg),
mri_->use_nodbg_end());
@ -996,12 +1002,12 @@ SimpleRegisterCoalescing::isWinToJoinCrossClass(unsigned SrcReg,
mri_->use_nodbg_end());
unsigned NewUses = SrcUses + DstUses;
unsigned NewSize = SrcSize + DstSize;
if (SrcRC != NewRC && SrcSize > NewRCCount) {
if (SrcRC != NewRC && SrcSize > ThresSize) {
unsigned SrcRCCount = allocatableRCRegs_[SrcRC].count();
if (NewUses*SrcSize*SrcRCCount > 2*SrcUses*NewSize*NewRCCount)
return false;
}
if (DstRC != NewRC && DstSize > NewRCCount) {
if (DstRC != NewRC && DstSize > ThresSize) {
unsigned DstRCCount = allocatableRCRegs_[DstRC].count();
if (NewUses*DstSize*DstRCCount > 2*DstUses*NewSize*NewRCCount)
return false;