Replace LiveInterval usage with LiveVariables. LiveIntervals
computes far more information than is needed for this pass
which just needs to find if an SGPR is live out of the
defining block.
LiveIntervals are not usually available that early, requiring
computing them twice which is very expensive. The extra run of
LiveIntervals/LiveVariables/SlotIndexes was costing in total
about 5% of compile time.
Continuing to use LiveIntervals is problematic. It seems
there is an option (early-live-intervals) to run the analysis
about where it should go to avoid recomputing LiveVariables,
but it seems to be completely broken with subreg liveness
enabled. There are also problems from trying to recompute
LiveIntervals since this seems to undo LiveVariables
and clearing kill flags, causing TwoAddressInstructions
to make bad decisions.
Insert the pass right after live variables and preserve it.
The tricky case to worry about might be phis since
LiveVariables doesn't count a register as live out if
in the successor block it is only used in a phi,
but I don't think this is a concern right now
because SIFixSGPRCopies replaces SGPR phis.
llvm-svn: 249087
When trying to fix SGPR live ranges, skip defs that are
killed in the same block as the def. I don't think
we need to worry about these cases as long as the
live ranges of the SGPRs in dominating blocks are
correct.
This reduces the number of elements the second
loop over the function needs to look at, and makes
it generally easier to understand. The second loop
also only considers if the live range is live
in to a block, which logically means it
must have been live out from another.
llvm-svn: 245150
True branch instructions do behave as expected with liveness.
Avoid the phrasing "branch decision is based on a value in an SGPR"
because this could be misleading. A VALU compare instruction's
result is still based on an SGPR, even though that condition
may be divergent.
llvm-svn: 245131
Matt Arsenault