From 829dd81377abfd0c02257ebd10d31bb0b1377815 Mon Sep 17 00:00:00 2001 From: "Arnaud A. de Grandmaison" Date: Tue, 4 Nov 2014 20:51:24 +0000 Subject: [PBQP] Tweak spill costs and coalescing benefits This patch improves how the different costs (register, interference, spill and coalescing) relates together. The assumption is now that: - coalescing (or any other "side effect" of reg alloc) is negative, and instead of being derived from a spill cost, they use the block frequency info. - spill costs are in the [MinSpillCost:+inf( range - register or interference costs are in [0.0:MinSpillCost( or +inf The current MinSpillCost is set to 10.0, which is a random value high enough that the current constraint builders do not need to worry about when settings costs. It would however be worth adding a normalization step for register and interference costs as the last step in the constraint builder chain to ensure they are not greater than SpillMinCost (unless this has some sense for some architectures). This would work well with the current builder pipeline, where all costs are tweaked relatively to each others, but could grow above MinSpillCost if the pipeline is deep enough. The current heuristic is tuned to depend rather on the number of uses of a live interval rather than a density of uses, as used by the greedy allocator. This heuristic provides a few percent improvement on a number of benchmarks (eembc, spec, ...) and will definitely need to change once spill placement is implemented: the current spill placement is really ineficient, so making the cost proportionnal to the number of use is a clear win. llvm-svn: 221292 --- llvm/lib/CodeGen/RegAllocGreedy.cpp | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) (limited to 'llvm/lib/CodeGen/RegAllocGreedy.cpp') diff --git a/llvm/lib/CodeGen/RegAllocGreedy.cpp b/llvm/lib/CodeGen/RegAllocGreedy.cpp index 1d081c748d4..dfeb9c04501 100644 --- a/llvm/lib/CodeGen/RegAllocGreedy.cpp +++ b/llvm/lib/CodeGen/RegAllocGreedy.cpp @@ -1789,9 +1789,11 @@ unsigned RAGreedy::tryLocalSplit(LiveInterval &VirtReg, AllocationOrder &Order, // instructions. // // Try to guess the size of the new interval. - const float EstWeight = normalizeSpillWeight(blockFreq * (NewGaps + 1), - Uses[SplitBefore].distance(Uses[SplitAfter]) + - (LiveBefore + LiveAfter)*SlotIndex::InstrDist); + const float EstWeight = normalizeSpillWeight( + blockFreq * (NewGaps + 1), + Uses[SplitBefore].distance(Uses[SplitAfter]) + + (LiveBefore + LiveAfter) * SlotIndex::InstrDist, + 1); // Would this split be possible to allocate? // Never allocate all gaps, we wouldn't be making progress. DEBUG(dbgs() << " w=" << EstWeight); -- cgit v1.2.3