171387 2017-04-27 12:47:05 -0700 AirLowerStackArgs: generate less code for large offsets 2017-04-27 12:47:05 -0700 1 1 1 Unclassified WebKit JavaScriptCore WebKit Nightly Build Unspecified Unspecified NEW P2 Normal --- 170215 1 jfbastien webkit-unassigned fpizlo jfbastien keith_miller mark.lam msaboff saam oldest_to_newest 1302241 0 jfbastien 2017-04-27 12:47:05 -0700 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.