Bug 171387
| Summary: | AirLowerStackArgs: generate less code for large offsets | ||
|---|---|---|---|
| Product: | WebKit | Reporter: | JF Bastien <jfbastien> |
| Component: | JavaScriptCore | Assignee: | Nobody <webkit-unassigned> |
| Status: | NEW | ||
| Severity: | Normal | CC: | fpizlo, jfbastien, keith_miller, mark.lam, msaboff, saam |
| Priority: | P2 | ||
| Version: | WebKit Nightly Build | ||
| Hardware: | Unspecified | ||
| OS: | Unspecified | ||
| Bug Depends on: | 170215 | ||
| Bug Blocks: | |||
JF Bastien
As part of bug #170215 I'm teaching AirowerStackArgs to handle large offsets from FP / SP on ARM, because it used to just assert.
We'll turn code such as:
Move (spill337), (spill201), %r0, @8735
Into:
Move $1404, %r16, @8736
Add64 %sp, %r16, @8736
Move (%r16), 2032(%sp), %r0, @8736
The code I'm writing for now will be silly and won't re-use r16 for large offsets even if it could.
This could be generated:
Move 1416(%sp), 2016(%sp), %r0, @8735
Move $1404, %r16, @8736
Add64 %sp, %r16, @8736
Move (%r16), 2032(%sp), %r0, @8736
Move 1400(%sp), 2024(%sp), %r0, @8737
Move 16(%r16), 2160(%sp), %r0, @8738
Move 360(%r16), 2280(%sp), %r0, @8739
Move 1376(%sp), 2080(%sp), %r0, @8740
Move 24(%r16), 2104(%sp), %r0, @8741
Move 1040(%sp), -208(%fp), %r0, @8742
Move 1360(%sp), 2200(%sp), %r0, @8743
Move 8(%r16), 2048(%sp), %r0, @8744
Move 1048(%sp), -248(%fp), %r0, @8745
Move 1328(%sp), -200(%fp), %r0, @8746
Move 1392(%sp), 2176(%sp), %r0, @8747
Move 1384(%sp), 2088(%sp), %r0, @8748
Move 32(%r16), 2096(%sp), %r0, @8749
Move 1344(%sp), 2328(%sp), %r0, @8750
Move 40(%r16), 2120(%sp), %r0, @8751
Move 56(%r16), 2240(%sp), %r0, @8752
Move 1312(%sp), -216(%fp), %r0, @8753
Move 1320(%sp), -232(%fp), %r0, @8754
Move 1336(%sp), 2248(%sp), %r0, @8755
Move 64(%r16), 2224(%sp), %r0, @8756
Move32 1356(%sp), %r1, @8757
The code simply needs to, per basic block:
- Track the last offset value generated in r16
- Invalidate on clobber (dest==r16 or writesPinned calls)
- If a new offset doesn't fit in addr, update the tracking value
This isn't super risky but also isn't worth doing in #170215.
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