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Re: [PATCH, PR83327] Fix liveness analysis in lra for spilled-into hard regs




On 12/15/2017 06:25 AM, Tom de Vries wrote:

Proposed Solution:

The patch addresses the problem, by:
- marking the hard regs that have been used in lra_spill in
  hard_regs_spilled_into
- using hard_regs_spilled_into in lra_create_live_ranges to
  make sure those registers are marked in the conflict_hard_regs
  of pseudos that overlap with the spill register usage

[ I've also tried an approach where I didn't use hard_regs_spilled_into, but tried to propagate all hard regs. I figured out that I needed to mask out eliminable_regset.  Also I needed to masked out lra_no_alloc_regs, but that could be due to gcn-specific problems (pointers take 2 hard regs), I'm not yet sure. Anyway, in the submitted patch I tried to avoid these problems and went for the more minimal approach. ]

Tom, thank you for the detail explanation of the problem and solutions you considered.  It helped me a lot.  Your simple solution is adequate as the most transformations and allocation are done on the 1st LRA subpasses iteration.
In order to get the patch accepted for trunk, I think we need:
- bootstrap and reg-test on x86_64
- build and reg-test on mips (the only primary platform that has the
  spill_class hook enabled)

Any comments?

The patch looks ok to me.  You can commit it after successful testing on x86-64 and mips but I am sure there will be no problems with x86-64 as it does not use spill_class currently (actually your patch might help to switch it on again for x86-64.  spill_class was quite useful for x86-64 performance on Intel processors).


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