[maglev] Don't merge phi taggings across a resumable loop header [v8/v8 : main]
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Victor Gomes (Gerrit)
Jul 24, 2026, 7:47:40 AM (21 hours ago) Jul 24
to Darius Mercadier, dmercadi...@chromium.org, leszek...@chromium.org, v8-re...@googlegroups.com, verwaes...@chromium.org, victorgo...@chromium.org
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Darius Mercadier (Gerrit)
Jul 24, 2026, 8:20:22 AM (21 hours ago) Jul 24
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File src/maglev/maglev-phi-representation-selector.cc
Line 1810, Patchset 3 (Latest):
if (omitted_backedge && new_block->state()->is_resumable_loop()) {Darius Mercadier . unresolved
Just `new_block->state()->is_resumable_loop()` should work, no? (and revert the rest of the change)
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Victor Gomes (Gerrit)
Jul 24, 2026, 8:31:35 AM (20 hours ago) Jul 24
to v8-s...@luci-project-accounts.iam.gserviceaccount.com, Darius Mercadier, dmercadi...@chromium.org, leszek...@chromium.org, v8-re...@googlegroups.com, verwaes...@chromium.org, victorgo...@chromium.org
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File-level comment, Patchset 3:
Victor Gomes . resolved
Done, reverted the rest.
Confirmed it's equivalent: is_resumable_loop() already implies is_loop(), and I ran mjsunit with a temporary DCHECK_EQ(omitted_backedge, new_block->is_loop()) here, which held over 8848 tests — so the extra condition was indeed redundant.
File src/maglev/maglev-phi-representation-selector.cc
Line 1810, Patchset 3:
if (omitted_backedge && new_block->state()->is_resumable_loop()) {Darius Mercadier . resolved
Just `new_block->state()->is_resumable_loop()` should work, no? (and revert the rest of the change)
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Darius Mercadier (Gerrit)
Jul 24, 2026, 8:34:47 AM (20 hours ago) Jul 24
to Victor Gomes, v8-s...@luci-project-accounts.iam.gserviceaccount.com, dmercadi...@chromium.org, leszek...@chromium.org, v8-re...@googlegroups.com, verwaes...@chromium.org, victorgo...@chromium.org
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v8-scoped@luci-project-accounts.iam.gserviceaccount.com (Gerrit)
Jul 24, 2026, 9:14:14 AM (20 hours ago) Jul 24
to Victor Gomes, Darius Mercadier, dmercadi...@chromium.org, leszek...@chromium.org, v8-re...@googlegroups.com, verwaes...@chromium.org, victorgo...@chromium.org
v8-s...@luci-project-accounts.iam.gserviceaccount.com submitted the change![]( "Open in Gerrit")
Change information
Commit message:
[maglev] Don't merge phi taggings across a resumable loop header
The phi-untagging snapshot table closes a loop-header merge phi by
making it its own backedge input, which assumes the header dominates its
backedge predecessor. A resumable loop is entered through the backedge
when the generator resumes, so the self-reference does not dominate;
report no tagging there instead and let it be recreated where needed.
Fixed: 537951967
Change-Id: I0c4d3c7601468c2db05ee822cf37a72f302db4fb
Commit-Queue: Darius Mercadier <dmerc...@chromium.org>
Reviewed-by: Darius Mercadier <dmerc...@chromium.org>
Auto-Submit: Victor Gomes <victo...@chromium.org>
Cr-Commit-Position: refs/heads/main@{#108864}
Files:
- M src/maglev/maglev-phi-representation-selector.cc
- A test/mjsunit/turbolev/regress-537951967.js
Change size: S
Delta: 2 files changed, 29 insertions(+), 0 deletions(-)
Branch: refs/heads/main
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Code-Review: +1 by Darius Mercadier
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