From 6e3b3e21227d3498d7f5d9d314a49a9ee4cbb873 Mon Sep 17 00:00:00 2001 From: Jakob Stoklund Olesen Date: Tue, 17 May 2011 16:38:37 +0000 Subject: [PATCH] Tweak cross-class coalescing to be more aggressive when the target class is small. 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 --- lib/CodeGen/SimpleRegisterCoalescing.cpp | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/lib/CodeGen/SimpleRegisterCoalescing.cpp b/lib/CodeGen/SimpleRegisterCoalescing.cpp index cebf4c9f4a5..1a2151fecf2 100644 --- a/lib/CodeGen/SimpleRegisterCoalescing.cpp +++ b/lib/CodeGen/SimpleRegisterCoalescing.cpp @@ -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;