A selection outside loops whose one arm only returns and whose other arm
branches to a join it does not dominate gets an empty block on that edge
as its merge (splitOneReturnJoin), but only when every other predecessor
of the join dominates the selection or is dominated by it. When the
parent selection's other arm is a region that ends in the same join, the
selection has no structured merge and the shader fails to recompile.
When every structurization attempt fails, Structurize now runs them again
and accepts that split for any join the selection does not dominate. The
split only inserts an empty block on the edge from the selection to the
join. Graphs that structurize on main keep their result.
A synthetic CFG and a synthetic program cover the shape; both fail on main
with "conditional block N has no structured merge".
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Fnrk5Dazjb2tLooVSpdRQq
Route semantic self-loops through a dedicated empty back-edge block. This prevents block merging from folding the continue target into the loop header when memory instructions emit nested selections. Add a synthetic loop-store regression that fails SPIR-V validation after optimization on main.
Keep the AlxcBTW #24 fallback as a separate guarded attempt before enabling shared-exit and nested-continuation repairs. Add the reduced padded shader reported by orishamir on #2523 as an end-to-end regression; the abstract graph does not reproduce the same failure.
A loop whose exit paths leave the loop construct before they meet got
the nearest common post-dominator of its exits as merge, and
splitSharedMergeBlocks never separated it. An exit continues the
enclosing loop, so its path to that merge runs through the outer
header again, or an exit enters a block that a branch before the loop
also reaches. splitOneLoopMerge gave the loop a forwarding merge block
each round, the other path still bypassed it, and the post-dominator
stayed the same block until "CFG shared merge splitting exceeded
budget". These shapes from #2642 fail that way on main, on d59a9167,
with #2471 and with both:
{{1}, {2}, {3, 4}, {2, 5}, {}, {1}}
{{1}, {2, 3}, {4, 5}, {}, {3, 6}, {1}, {2}}
{{1, 3}, {2, 4}, {3, 1}, {4}, {}}
{{1, 2}, {3, 2}, {4}, {4, 1}, {}}
{{1, 2}, {4}, {3, 1}, {4, 2}, {}}
When the plain and the privatized pass both fail, Structurize now runs
a third pass. It routes such a loop's exits through one junction with
routeLoopExits, as loops whose exits have no common post-dominator are
routed already, and gives an outer loop whose only latch lies in an
inner loop its own continue block. In that pass a loop exit conditional
that is neither a direct break or continue nor has an exit tail of its
own is structured as a selection, and an exit tail that the other arm
reaches is not used as one. Without that, graphs the routing unblocks
keep a conditional without merge (the rule from #2762) or a selection
entered past its header. Graphs that the first two passes structure
are unchanged, and when the third pass fails too, the second pass's
error is reported.
Differential fuzz against main, reducible graphs with 5 to 9 blocks,
each with 0 estimated words per block and again with one block at 1000
words (the privatizeSharedReturns path). Oracle: exact post-dominators,
requireStructuredBranches, merges dominated by their headers, the same
executions as the original graph, and spirv-val (SPIRV-Tools v2026.4,
Vulkan 1.3) on a module emitted from the structured graph.
- 200,000 random graphs. main structures 178,743 (0 words) and 178,750
(1000 words); the output is identical on all of them. Of main's
14,256 and 14,311 budget failures 13,527 and 13,596 now structure,
and 2,576 and 2,565 of its refusals. No new output is invalid. The
invalid outputs are main's 530, plus at 1000 words one graph that
d59a9167 already turns from a budget failure into a back edge to a
block that is not a loop header.
- 24,000 structured programs from orishamir/anyps5-cfgfuzz's
generator (if/else, loops, break, continue, return). main structures
21,093 and 21,022; the output is identical. 619 of 2,448 and 634 of
2,429 budget failures now structure. No new output is invalid; the
invalid outputs are main's 92.
agc_structurizer has the five shapes; requireOriginalBranches now
follows route variables. agc_shader_control_flow has two RDNA programs
of the first two shapes. The non-GPU tests and the 253 agc_driver GPU
tests pass on Windows (RTX 5070 Laptop).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
A selection in a loop whose arms both reach their nearest common
post-dominator within the iteration got that post-dominator as its
merge. When an arm can also continue the loop, the post-dominator
follows the back edge: the continuing path re-enters the loop header
and reaches the outer selection's merge without passing the block where
the arms meet. In the loop {1}, {2, 4}, {3, 4}, {4, 5}, {1, 6}, {1}, {}
from #2642 (latches 4 and 5) the selections at 1 and 2 both merged at 4.
splitSharedMergeBlocks gave 2 a forwarding merge block, recomputed 4 for
it because 3 continues through 5, and repeated until "CFG shared merge
splitting exceeded budget: originalBlocks=9 currentBlocks=45
splitBudget=36".
When that post-dominator is inside the loop construct, findSelectionMerge
now takes the arms' nearest common post-dominator over the paths of the
iteration that reach it, so paths that leave through the continue block
or the loop's merge no longer move the merge past the arms' join. When
no arm leaves early the result is the same block as before. The loop
structures with two forwarding blocks and no clones or route variables;
so do three latches, the selections on the false side, and an if-else
whose one arm continues.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Reuse the prerequisite call-region analysis for signed relative calls, including callees after s_endpgm. Lower the saved link as shader base plus PC+4 and reject unsupported targets and call shapes.
Add decoder, IR, CFG and Vulkan execution regressions. Seven focused CMake tests pass; five layouts cover 15 dispatches and 3,200 output comparisons on lavapipe. Record ISA sources and native RDNA2/PS5 limits in TechnicalDebt.
Decodes SOP1 0x21 s_swappc_b64 (link pair = pc + 4) and resolves its call/return pairing through the existing s_setpc_b64 path: static call regions in GraphBuilder and the vertex-entry fetch-shader call inlined from the parsed fetch-shader plan. s_call_b64 (SOPK 0x16) and s_rfe_b64 (SOP1 0x22) throw at decode. Unmodeled cases throw; see docs/dev/TechnicalDebt.md.
A selection inside a loop whose arm either joins the other target or
continues/breaks (`if (a) { if (b) continue; x; }`) got the nearest
common post-dominator as its merge. When the loop exits after the outer
join, that is the outer selection's merge, so both selections shared
it. splitSharedMergeBlocks then inserted a forwarding block in front of
it, recomputed the same merge, and repeated until the budget ran out:
PPSA14632's compute shader 0x1a80ee0000 stopped with "CFG shared merge
splitting exceeded budget: originalBlocks=92 currentBlocks=460".
findSelectionMerge now picks the joined target when the other arm is a
conditional block with the header as its only predecessor, and every
successor of that arm is the joined target or the loop's continue or
merge block. The shader structures with 13 added blocks and no clones
or route variables.
In the result the outer selection header dominates the loop's continue
target, so the test's verifyStructured counted the continue target as a
selection member that branches outside (back to the loop header).
SPIR-V uses structural dominance, where the loop header's edge to its
continue target keeps it out of the selection, so verifyStructured now
skips the continue construct of an enclosing loop. spirv-val accepts
the new test's SPIR-V for both subgroup sizes.
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").
SOP1 opcode 33 with SDST null keeps no return address, so it is exactly
s_setpc_b64; the decoder now reads it that way, as KytyPS5 does. A call
with a real destination still throws "unsupported SOP1 opcode 33".
GraphBuilder resolves two more jump shapes. A long branch is
s_getpc_b64 and s_add_u32/s_addc_u32 or s_sub_u32/s_subb_u32
immediates, also through vcc, all in one block. A dword jump table
branches to the table base minus an entry that s_load_dword reads at an
index bounded by s_min_u32 and scaled by 4; the resolver follows
register writes back through straight-line code, and anything else is
still refused. The code table load now also handles one-dword entries.
agc_shader_control_flow checks the decode, the graphs and the refusals;
the new agc_driver_scalar_swappc runs all shapes on the GPU.
The decoder stopped at an s_endpgm unless the next word was a known branch
target. When an earlier branch jumps further than that word, the block right
after the s_endpgm is entered only from later code, so the program was cut
short and the graph builder rejected the branch as targeting an invalid
program counter. Stop only when no decoded branch targets a word at or past
the one after the s_endpgm.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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 selection whose region (the blocks reachable from its arms before its
merge) is also entered from outside the header cannot be expressed as a
SPIR-V selection construct, and the structurizer gave up with "semantic
block cloning is disabled". Pixel shaders hit this through a shared
discard tail (s_mov_b64 exec, 0 / exp null / s_endpgm) that several
selections branch to, compute shaders through short-circuit conditions
that jump into a shared body, and ray-traced compute passes through an
s_cbranch_execz that skips past a join into the middle of a selection.
Such a region is made single-entry in one of two ways, chosen per region
by its estimated translated size:
- Cloning (node splitting): the blocks the outside edges reach inside the
region are copied and the outside edges redirected to the copies. When
the header's merge is a shared linear return tail, giving the header a
private copy of that tail is tried first. Each block now carries an
estimate of the SPIR-V words it translates to. The per-instruction
weights come from a fit of the recompiler's per-block output (before
spirv-opt, phis excluded) over 8,300 blocks of captured shaders: VALU
60, buffer and flat 120, SMEM 180, image 220, LDS 400. SALU (8) and
exports (20) fit near zero and keep a small weight. Lane ops (120) and
image_bvh_intersect_ray (2000) were too rare there to fit and are
weighted for the wave and traversal expansions they need. A region is cloned only when it is at most 1024 estimated
words and at most an eighth of the program (at least 256), and while
all clones stay within a quarter of the program.
- Routing through a junction, for larger regions: every edge into the
entered part (from outside, and from the header's own arms) and every
edge from the arms to the merge is sent through a new empty junction
block. Each rerouted edge first passes empty blocks that assign
Boolean route variables (the IR's goto variables); the junction tests
them in order to reach the edge's original target. The entered part
then follows the junction and is emitted once. Branch conditions are
still evaluated only at the end of their original blocks: a route
variable records the edge a block already took, so a later SCC, VCC or
EXEC write cannot change the route, and in the two-lane wave64 layout
the source branch is combined across both halves as before while the
route variable holds the same constant in both. Routing is refused
when a rerouted edge is a back edge or leaves an indirect branch, when
the region wraps around to a dominating block, or when it would change
the natural loops or make the graph irreducible; cloning bounded by the
program's estimated size is the fallback, and otherwise it throws with
the header, the entered block and both reasons.
Selections whose arms only meet again after private return tails had no
post-dominator merge. When the existing rules find none, the merge is
now looked up with edges into private return tails ignored, or taken as
the other arm when one arm only returns; the candidate must still exit
the construct only through the merge. applyBlockOrder also remaps
indirect branch targets.
agc_shader_control_flow_tests (under ctest) covers hand-assembled
gfx1030 programs: the cloned shapes above, and routed ones (an
s_cbranch_execz into an expensive region with a loop, a region inside a
loop, nested entered regions, a shared body reached after SCC is
overwritten, early returns beside an entered region, an arm that only
returns). It checks that every selection construct exits only through
its merge, follows route variables to check that the structured graph
runs the same instruction ranges under the same branch conditions as
the original, bounds the cloned instructions, recompiles each program
for 64- and 32-lane subgroups, and keeps the routed execz program within
10% of the SPIR-V of the same program without the entering branch.
Given .req files it checks their graphs instead. agc_shader_replay --cfg
prints a request's graph, now with each block's estimate, before and
after structurization.
Jan Šlégl
Mouhand Kaddo
Scramblrrrr
AlxcBTW
Adrià
MarcZX100
Chad
Sanjaysrinivas
ebosido444-ai
alfalfa-star
Dean
Celegans12
DotDebian
Dean Galvin