|
More or less as proposed in its ninth iteration with the
addition of a gcmmove() functionality to restore coherent
local schedules.
Changes since RFC 8:
Features:
- generalization of phi 1/0 detection
- collapse linear jmp chains before GVN; simplifies if-graph
detection used in 0/non-0 value inference and if-elim...
- infer 0/non-0 values from dominating blk jnz; eliminates
redundant cmp eq/ne 0 and associated jnz/blocks, for example
redundant null pointer checks (hare codebase likes this)
- remove (emergent) empty if-then-else graphlets between GVN and
GCM; improves GCM instruction placement, particularly cmps.
- merge %addr =l add %addr1, N sequences - reduces tmp count,
register pressure.
- squash consecutive associative ops with constant args, e.g.
t1 = add t, N ... t2 = add t2, M -> t2 = add t, N+M
Bug Fixes:
- remove "cmp eq/ne of non-identical RCon's " in copyref().
RCon's are not guaranteed to be dedup'ed, and symbols can
alias.
Codebase:
- moved some stuff into cfg.c including blkmerge()
- some refactoring in gvn.c
- simplification of reassoc.c - always reassoc all cmp ops
and Kl add %t, N. Better on coremark, smaller codebase.
- minor simplification of movins() - use vins
Testing - standard QBE, cproc, hare, harec, coremark
[still have Rust build issues with latest roland]
Benchmark
- coremark is ~15%+ faster than master
- hare "HARETEST_INCLUDE='slow' make check" ~8% faster
(crypto::sha1::sha1_1gb is biggest obvious win - ~25% faster)
Changes since RFC 7:
Bug fixes:
- remove isbad4gcm() in GVN/GCM - it is unsound due to different state
at GVN vs GCM time; replace with "reassociation" pass after GCM
- fix intra-blk use-before-def after GCM
- prevent GVN from deduping trapping instructions cos GCM will not
move them
- remove cmp eq/ne identical arg copy detection for floating point, it
is not valid for NaN
- fix cges/cged flagged as commutative in ops.h instead of cnes/cned
respectively; just a typo
Minor features:
- copy detection handles cmp le/lt/ge/gt with identical args
- treat (integer) div/rem by non-zero constant as non-trapping
- eliminate add N/sub N pairs in copy detection
- maintain accurate tmp use in GVN; not strictly necessary but enables
interim global state sanity checking
- "reassociation" of trivial constant offset load/store addresses, and
cmp ops with point-of-use in pass after GCM
- normalise commutative op arg order - e.g. op con, tmp -> op tmp, con
to simplify copy detection and GVN instruction dedup
Codebase:
- split out core copy detection and constant folding (back) out into
copy.c, fold.c respectively; gvn.c was getting monolithic
- generic support for instruction moving in ins.c - used by GCM and
reassoc
- new reassociation pass in reassoc.c
- other minor clean-up/refactor
Changes since RFC 6:
- More ext elimination in GVN by examination of def and use bit width
- elimination of redundant and mask by bit width examination
- Incorporation of Song's patch
Changes since RFC 5:
- avoidance of "bad" candidates for GVN/GCM - trivial address offset
calculations, and comparisons
- more copy detection mostly around boolean values
- allow elimination of unused load, alloc, trapping instructions
- detection of trivial boolean v ? 1 : 0 phi patterns
- bug fix for (removal of) "chg" optimisation in ins recreation - it
was missing removal of unused instructions in some cases
ifelim() between GVN and GCM; deeper nopunused()
|
