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Revert "[maglev] Fix dead fallthrough merging"

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This reverts commit c7aef55208.

Reason for revert: Merged the wrong CL for the fix.

Original change's description:
> [maglev] Fix dead fallthrough merging
>
> Add a method which optionally merges dead fallthrough paths, in case the
> iteration in EmitUnconditionalDeopt reaches a merge point that is live
> from another jump but dead on the fallthrough.
>
> Bug: v8:7700
> Change-Id: Ie505cd5356fcf70208f2f6d3e52b805956485f74
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3663086
> Auto-Submit: Leszek Swirski <leszeks@chromium.org>
> Commit-Queue: Toon Verwaest <verwaest@chromium.org>
> Reviewed-by: Toon Verwaest <verwaest@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#80878}

Bug: v8:7700
Change-Id: I75a21777aecfa08138fcc25a882ae109f3409159
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3687649
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#80917}
This commit is contained in:
Leszek Swirski 2022-06-02 15:13:04 +00:00 committed by V8 LUCI CQ
parent 56dd286445
commit 403dc1e019
2 changed files with 1 additions and 20 deletions
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4
src/maglev/maglev-graph-builder.h
View File

@ -151,10 +151,6 @@ class MaglevGraphBuilder {
// Loops that are unreachable aside from their back-edge are going to
// be entirely unreachable, thanks to irreducibility.
if (!merge_states_[iterator_.current_offset()]->is_unreachable_loop()) {
// We might be falling through into this merge state, so merge in that
// fallthrough as dead, if necessary.
merge_states_[iterator_.current_offset()]->MaybeMergeDeadFallthrough(
*compilation_unit_, iterator_.current_offset());
break;
}
}

17
src/maglev/maglev-interpreter-frame-state.h
View File

@ -325,18 +325,6 @@ class MergePointInterpreterFrameState {
});
}
// Merges a dead fallthrough framestate (e.g. one which has been early
// terminated with a deopt), if that merge is needed. It is needed when there
// is exactly one missing predecessor.
void MaybeMergeDeadFallthrough(const MaglevCompilationUnit& compilation_unit,
int merge_offset) {
// We've seen all predecessors, so we're good.
if (predecessors_so_far_ == predecessor_count_) return;
// Otherwise exactly one should be missing.
DCHECK_EQ(predecessors_so_far_, predecessor_count_ - 1);
MergeDead(compilation_unit, merge_offset);
}
// Merges a dead loop framestate (e.g. one where the block containing the
// JumpLoop has been early terminated with a deopt).
void MergeDeadLoop() {
@ -368,10 +356,7 @@ class MergePointInterpreterFrameState {
}
bool is_unreachable_loop() const {
// We should have either merged or removed all predecessors, except maybe
// the fallthrough.
DCHECK_GE(predecessors_so_far_, predecessor_count_ - 1);
DCHECK_LE(predecessors_so_far_, predecessor_count_);
DCHECK_EQ(predecessors_so_far_, predecessor_count_);
// If there is only one predecessor, and it's not set, then this is a loop
// merge with no forward control flow entering it.
return predecessor_count_ == 1 &&