Intersect copied fixed-point sets without allocating each intermediate.
Preserve sorted results and the existing analysis iteration order.
Compact oversized storage only when publishing a changed set.
Keep an allocating control switch outside the cache key.
Compare complete fixed points over empty intersections, loops and DAGs.
Register the same equivalence fixtures for the allocating control.
Both dominance analyses start from sorted unique sets and intersect them.
Insert the current block ID with lower_bound instead of sorting again.
Preserve every intermediate set and the existing ID-order iteration.
Keep the generic unsorted helper and all graph rewrite logic unchanged.
Compare both analyses against the original algorithms on six raw CFGs.
Cover finite loops, closed SCCs, unreachable islands and permuted IDs.
A pixel shader whose early discards branch to one small ending block
gave that block several conditional predecessors outside any loop, and
structurizing failed. When the regular pass throws, the structurizer
restarts from the original graph and first gives each conditional
predecessor its own copy of such a return block (within the clone word
floor and a budget of four clones per block).
Uncharted: Legacy of Thieves Collection (PPSA05684) stopped at such a pixel shader with "conditional block 15 has no structured merge".
computePostDominators iterates its sets to a fixed point, visiting the
blocks in id order. Post-dominance flows from a block's successors back to
it, and successors mostly have higher ids, so each pass moved the sets back
by about one block: a long program needed about as many passes as it has
blocks, each costing O(blocks^2). recomputeAnalyses runs it after every
split of splitSharedMergeBlocks, up to four times per block.
Visit the blocks in post-order of the CFG (successors first), then any the
entry does not reach. The sets start from every block and only shrink, so
the iteration still converges to the same greatest fixed point, now in a
few passes.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
A loop whose exits have no common post-dominator, such as a normal exit
to one s_endpgm tail beside an early-out to a kill tail, got no merge
block, and Structurize threw "loop at block N has no structured
merge/continue". With three or more exits, detectNaturalLoops threw
first, on a lookup of InvalidControlFlowId.
Such a loop now leaves through one new merge block that dispatches on
route variables. They are cleared before the header and set on each
exit edge to a target other than the latch's exit. Inner loops are
routed first; a routing that would change the natural loops throws.
A loop-exit tail branch whose in-body target is the continue block no
longer merges there, which spirv-val rejects ("Header block ... is
contained in the loop construct ..., but its merge block ... is not").
A selection whose one arm only returns (kill or s_endpgm) and whose other
arm branches straight to the merge of an enclosing selection had no
structured merge, so the draw was skipped. PPSA21564's BotEye G-buffer
pixel shaders (eight variants) have this shape.
When no other split applies, the edge from such a header to the shared
join is now split into an empty block, which becomes the header's merge.
A conditional inside a loop with one target in the loop body and the
other outside it was taken for a break and emitted without a merge. When
the outside target is not the loop's merge but a tail of blocks that
reaches it, SPIR-V has no construct for that branch: spirv-val rejects
the module ("Selection must be structured") and the driver is free to
compile it into anything.
Such a branch now merges at its in-body target when the tail is private
to it (every tail block is dominated by the tail's first block, stays in
the loop construct and leaves only for the loop's merge), so the tail is
an "if (c) { tail; break; }" the loop already allows. Merges are given
to these after every other construct's, and one already taken leaves the
branch as before.
All 13 PPSA21564 programs whose V#s are read from GPU memory (the
deferred lighting and ray-traced passes) had two such branches in their
traversal loops. With this change none of the 74 dumped title programs
has one, and the 209 modules of a title-to-cinematic run validate apart
from three unrelated image-offset and entry-point errors.
Tests: agc_structurizer_tests structures a loop that exits through one
tail block and a loop with two exit tails, and requires every merge-less
conditional to target its loop's merge or continue.
Only the lines this branch added lose their comments; the commits before
keep them, with the reasoning behind each change, for whoever digs into
that code later.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
findSelectionMerge took the nearest common post-dominator of a selection's
targets, computed across the loop's back edge. When one arm only continues
(reaching that block in a later iteration) and the other target is shared
with an enclosing selection, the shared merge was split off the header, the
post-dominator stayed where it was, and splitting repeated until the budget
threw.
Inside a loop, an arm that reaches the post-dominator only past the continue
or merge block now leaves the selection by continuing, and the merge is the
other arm's target; after one split that is the header's own synthetic merge.
agc_structurizer_tests builds the smallest such graph; it hit the budget
before.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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