wasm: decline an inlined region carrying an unarmed CALL_ASSEMBLER - #1355
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Accepting an inline ran `build_wasm_module` over the merged candidate as an eligibility trial, and `reemit_loop` then ran the same build over the same candidate to produce the module it installs. The trial's own bytes were discarded; only its `Ok`/`Err` was read. Nothing `reemit_loop` does before that build needs unwinding on failure: it reads the fail-index base and allocates a bridge-cell array that is dropped on the error path. The two destructive steps at the call site — dropping the guard's direct-dispatch slot and zeroing its cell — were already restored by the existing error arm. So the install runs directly and its build answers the eligibility question. `classify_inline_install_error` keeps the per-shortage decline tallies the host prints, and routes a module-replacement rejection to the re-emission counter instead. Executed wasm ops with `PYRE_WASM_INLINE_BRIDGE=1`, over all 431 synthetic fixtures: aggregate -0.090%, and -0.41% mean over the 75 fixtures that accept an inline. Per fixture the saving is 1.6M to 14.2M ops per accepted inline (nested_callee_chain_mutation_abort -2.42%, nested_loop_correctness -1.92%, float_pow_overflow_exp -1.30%, subscr_negative_index_deopt -1.11%). No fixture moves more than +0.15%, stdout is identical on all 431, and every fixture reports the same `inline_ok` count as before. Assisted-by: Claude
… space `rebase_region_value_ids` shifts a region's value ids with `OpRef::with_raw`, which preserves the variant. The wasm emitters classify by raw payload (`OpRef::raw_is_constant`), so an id shifted to or past `1 << 31` stops naming a value local and reads as a constant, and one shifted past the `TempVar` sentinel base would size `ValueLocals` by a near-`u32::MAX` id. `OpRef::VALUE_ID_LIMIT` names one past the highest raw an ordinary value id may carry, and the rebase declines when `offset + width` exceeds it. Equality is admitted: `width` is one past the region's last id. Reported by CodeRabbit on #1342. Assisted-by: Claude
…mission The region fixture passed an empty pool on both sides, so the constant-window replay in `build_wasm_module` never ran under test: mutating either arm — the insert at `id + offset`, and the removal of an owner key that lands inside the window — left the suite green. The region now reads a value with no producing op, bound only by its own pool, so the insert is what makes the module build; and a third build gives the owner pool a key inside the region's window with the region's own seed removed, which must reach the "read with no producing op" decline rather than answer the read with the owner's unrelated bits. Both mutations now fail the test. `build` also builds the same `ModuleBuildInputs` twice and asserts the bytes match, because `reemit_loop` rebases the same retained regions on every re-emission. Reported by CodeRabbit on #1342. Assisted-by: Claude
`CaParams` is decided when the owner loop is compiled and `reemit_loop` reuses the owner's stored `ModuleBuildInputs` verbatim, so a region merged in later brings a callee that is absent from `ca.targets`. The dedicated CALL_ASSEMBLER arm is guarded on `ca.emit_ca`; an op that misses it falls through to the ordinary residual-call arm, which lowers arg 0 as an `__indirect_function_table` slot, while a CALL_ASSEMBLER's arg 0 is the callee's first frame slot. `build_wasm_module` now rejects such a region in the loop that validates the merged stream, and `classify_inline_install_error` routes the decline to `BRIDGE_DIAG[49]` / `inline_decl_call_assembler`. Assisted-by: Claude
`jit_call_trampoline_inner` answered a `table.get` miss by writing 0 into the call area's result slot and returning Ok. For a Ref result that 0 is indistinguishable from a null Ref the callee returned, so a call lowered against the wrong operand was answered with a plausible value rather than trapping. The miss now names the slot once per distinct value; the value written is unchanged. Assisted-by: Claude
WalkthroughThe WASM backend now validates inline bridge value-ID rebasing and ChangesWASM bridge validation and diagnostics
Estimated code review effort: 4 (Complex) | ~45 minutes Merge Risk: ⚪ Minimal · up to The change prevents unsafe inlining of unsupported CALL_ASSEMBLER regions while preserving eligible inlining and the default path. No actionable merge-blocking risk remains; a trivial follow-up may improve one regression test's coverage of the documented mismatch case. Possibly related PRs
Sequence Diagram(s)sequenceDiagram
participant InlineInstaller
participant reemit_loop
participant BridgeState
participant Diagnostics
InlineInstaller->>BridgeState: clear dispatch cell and re-emission metadata
InlineInstaller->>reemit_loop: install candidate and re-emit
reemit_loop-->>InlineInstaller: success or failure
alt Re-emission succeeds
InlineInstaller->>BridgeState: retain candidate and register GC metadata
else Re-emission fails
InlineInstaller->>BridgeState: restore previous candidate and bridge slot
InlineInstaller->>Diagnostics: record and classify failure
end
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Inline comments:
In `@majit/majit-backend-wasm/tests/codegen_test.rs`:
- Around line 1414-1423: Update region_ops so the CALL_ASSEMBLER operation
created through make_op carries a call descriptor with a target token, allowing
build_wasm_module to resolve a registered token before checking ca.targets.
Preserve the first CaParams case for a missing CA arm and ensure the second case
specifically exercises a target absent from the arm’s table; otherwise reword
its comment to describe the actual missing-token coverage.
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`INLINE_BRIDGE_ENABLED` starts true. `inline_bridge_enable` becomes `inline_bridge_disable`, the guest export becomes `pyre_jit_inline_bridge_disable`, and the runner calls it only when `PYRE_WASM_INLINE_BRIDGE` reads `0`, `false` or `off` — the shape `PYRE_WASM_BRIDGE_PARAMS` already uses. Measured on this tree with the guest and runner built from it, over the 435 fixtures `pyre/check.py --backend wasm` runs: flag off 435/435; inlining on, 434 passed and one jit-stats gate reporting `guard_failures 1972 -> 1938` on `synth/short_circuit_side_effects`. That baseline is re-recorded, and the run is 435/435 with it. `pyre/check.snap` is unchanged, so no fixture's output moved. Turning the default on produces the same fixture and the same counters as setting the environment variable did. Wall-clock over 441 fixtures, arms interleaved and each summarised by its minimum: total execution 77.82s -> 77.49s, 23 fixtures more than 5% and 5ms slower, 18 the same amount faster, no output mismatches. Against the wasm and dynasm execution times of the ubuntu `check.py` run on PR #1355, the fixtures over a 3.0 ratio go from six to three, and none crosses upward. `PYRE_WASM_REEMIT` keeps its own default: the inline path calls `reemit_loop` without consulting it, and the arm it still gates alone is the one-shot identity re-emission probe. Its gate-triage entry is rewritten to say that, and `PYRE_WASM_INLINE_BRIDGE` moves to the default-ON section. Assisted-by: Claude
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`INLINE_BRIDGE_ENABLED` starts true. `inline_bridge_enable` becomes `inline_bridge_disable`, the guest export becomes `pyre_jit_inline_bridge_disable`, and the runner calls it only when `PYRE_WASM_INLINE_BRIDGE` reads `0`, `false` or `off` — the shape `PYRE_WASM_BRIDGE_PARAMS` already uses. Measured on this tree with the guest and runner built from it, over the 435 fixtures `pyre/check.py --backend wasm` runs: flag off 435/435; inlining on, 434 passed and one jit-stats gate reporting `guard_failures 1972 -> 1938` on `synth/short_circuit_side_effects`. That baseline is re-recorded, and the run is 435/435 with it. `pyre/check.snap` is unchanged, so no fixture's output moved. Turning the default on produces the same fixture and the same counters as setting the environment variable did. Wall-clock over 441 fixtures, arms interleaved and each summarised by its minimum: total execution 77.82s -> 77.49s, 23 fixtures more than 5% and 5ms slower, 18 the same amount faster, no output mismatches. Against the wasm and dynasm execution times of the ubuntu `check.py` run on PR #1355, the fixtures over a 3.0 ratio go from six to three, and none crosses upward. `PYRE_WASM_REEMIT` keeps its own default: the inline path calls `reemit_loop` without consulting it, and the arm it still gates alone is the one-shot identity re-emission probe. Its gate-triage entry is rewritten to say that, and `PYRE_WASM_INLINE_BRIDGE` moves to the default-ON section. Assisted-by: Claude
youknowone
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`INLINE_BRIDGE_ENABLED` starts true. `inline_bridge_enable` becomes `inline_bridge_disable`, the guest export becomes `pyre_jit_inline_bridge_disable`, and the runner calls it only when `PYRE_WASM_INLINE_BRIDGE` reads `0`, `false` or `off` — the shape `PYRE_WASM_BRIDGE_PARAMS` already uses. Measured on this tree with the guest and runner built from it, over the 435 fixtures `pyre/check.py --backend wasm` runs: flag off 435/435; inlining on, 434 passed and one jit-stats gate reporting `guard_failures 1972 -> 1938` on `synth/short_circuit_side_effects`. That baseline is re-recorded, and the run is 435/435 with it. `pyre/check.snap` is unchanged, so no fixture's output moved. Turning the default on produces the same fixture and the same counters as setting the environment variable did. Wall-clock over 441 fixtures, arms interleaved and each summarised by its minimum: total execution 77.82s -> 77.49s, 23 fixtures more than 5% and 5ms slower, 18 the same amount faster, no output mismatches. Against the wasm and dynasm execution times of the ubuntu `check.py` run on PR #1355, the fixtures over a 3.0 ratio go from six to three, and none crosses upward. `PYRE_WASM_REEMIT` keeps its own default: the inline path calls `reemit_loop` without consulting it, and the arm it still gates alone is the one-shot identity re-emission probe. Its gate-triage entry is rewritten to say that, and `PYRE_WASM_INLINE_BRIDGE` moves to the default-ON section. Assisted-by: Claude
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* test(wasm): give the declined region's CALL_ASSEMBLER a real callee token
`make_op` attaches no descr, so `call_target_token` answered `None` and both
arms of the decline test stopped at the missing token. The `emit_ca: true`
arm never reached the `ca.targets` membership check it was written for.
A local `TargetTokenCallDescr` supplies the token `SimpleCallDescr` cannot,
and the cases are now: no arm emitted, an arm emitted for other callees, and
an op naming no callee. Removing the membership clause makes the middle case
panic in the CA arm's `expect("CA op target must be registered")`, which is
the reachability the previous version lacked.
Assisted-by: Claude
* majit: register an inlined region's quasi-immutable deps on the flag it reads
A loop-closing bridge accepted for inlining is installed by rebuilding its
owner, and the wasm `compile_bridge` returns from that arm above
`mint_bridge_invalidation_flag`. The merged module keeps the owner's
`invalidated_flag_addr`, so the region's GUARD_NOT_INVALIDATED loads the root
flag, while the bridge arms of the metainterp record
`latest_bridge_invalidation_flag()` as the generation that compile produced.
That is an earlier bridge's flag, or `None` when the token has none yet, and
`register_quasi_immutable_deps` returns without registering anything on `None`.
`QuasiImmut::invalidate` only stores into the flags registered with it, so the
root the region reads is not among them.
`JitCellToken::record_bridge_invalidation_flag` records an existing flag as
that generation instead of minting one. The inline arm records the root flag,
so the dependencies collected while tracing the region land on the address the
merged code loads. A flag already at the end of the list is not pushed again.
Assisted-by: Claude
* wasm: make loop-closing bridge inlining the default, with a host opt-out
`INLINE_BRIDGE_ENABLED` starts true. `inline_bridge_enable` becomes
`inline_bridge_disable`, the guest export becomes
`pyre_jit_inline_bridge_disable`, and the runner calls it only when
`PYRE_WASM_INLINE_BRIDGE` reads `0`, `false` or `off` — the shape
`PYRE_WASM_BRIDGE_PARAMS` already uses.
Measured on this tree with the guest and runner built from it, over the 435
fixtures `pyre/check.py --backend wasm` runs: flag off 435/435; inlining on,
434 passed and one jit-stats gate reporting `guard_failures 1972 -> 1938` on
`synth/short_circuit_side_effects`. That baseline is re-recorded, and the run
is 435/435 with it. `pyre/check.snap` is unchanged, so no fixture's output
moved. Turning the default on produces the same fixture and the same counters
as setting the environment variable did.
Wall-clock over 441 fixtures, arms interleaved and each summarised by its
minimum: total execution 77.82s -> 77.49s, 23 fixtures more than 5% and 5ms
slower, 18 the same amount faster, no output mismatches. Against the wasm and
dynasm execution times of the ubuntu `check.py` run on PR #1355, the fixtures
over a 3.0 ratio go from six to three, and none crosses upward.
`PYRE_WASM_REEMIT` keeps its own default: the inline path calls `reemit_loop`
without consulting it, and the arm it still gates alone is the one-shot
identity re-emission probe. Its gate-triage entry is rewritten to say that, and
`PYRE_WASM_INLINE_BRIDGE` moves to the default-ON section.
Assisted-by: Claude
* wasm: decline inlining a bridge into an invalidated owner
An accepted loop-closing region has no code of its own: it runs from the
owner's module, whose GUARD_NOT_INVALIDATED reads the flag baked at
`compile_loop` — the owner's root flag. When the owner is already
invalidated that flag is set, so `compile_bridge` now declines the inline
arm on `is_invalidated()` (BRIDGE_DIAG 50,
`inline_decl_owner_invalidated`) and the out-of-line path mints a clear
generation. `runner_test.py test_guard_not_invalidated` steps 3-4 compile
a bridge after `invalidate_loop` and assert its guard does not fire until
a second `invalidate_loop`.
Add host-side tests driving `Backend::compile_loop` and
`Backend::compile_bridge`: one where the owner is valid and the inline
trial is reached, one where it is invalidated and the trial is declined.
They share a mutex because the global fail-descr registry is appended to
under a no-interleaving assumption. Extend the token unit test with the
recorded-root-flag case that motivates the decline.
Assisted-by: Claude
* wasm: state why an inlined region reports a zero AsmInfo
`model.py:67 compile_bridge` permits `None`, and the consumers read the
result as debug data — `interp_resop.py:253-255` defaults `asmaddr` and
`asmlen` to 0 when it is absent.
Assisted-by: Claude
* test(wasm): accept an inlined region as a compiled formerly-declined bridge
`wasm_outlier_bridges_stay_compiled_at_runtime` asserted `BRIDGE_OK > 0` for
`exception_oserror_fields.py`. With loop-closing bridge inlining on by default
that region is merged into its owner instead, so the run reports
`BRIDGE_OK=0 inline_ok=1` and the assertion failed; `PYRE_WASM_INLINE_BRIDGE=0`
on the same binary reports `BRIDGE_OK=1 inline_ok=0`.
Assert over both counters for that fixture.
Assisted-by: Claude
* wasm: log why each loop-closing bridge was refused a merge
`bridge_diag` counts inline-bridge declines by reason but carries no key that
says which declines matter. Record one line per decline — the bridge's own
trace id, the source trace and fail index, and the `(slot, key)` of the
crossing the decline leaves in place — in a capped buffer, exported as a string
and printed with the rest of the stats.
`(slot, key)` joins a record against `PYRE_WASM_TRACE_ENTRY_CENSUS`, so a
decline can be weighted by how often its crossing actually ran. On fannkuch the
join reads: 6 `not_header` declines belong to the three traces that own
18.45M of the 20.57M key>0 trace entries, while all 9 `not_direct` declines
belong to traces with no key>0 entries at all.
Assisted-by: Claude
* wasm: resolve a merged stream's loop label from the owner's JUMP
`find_loop_label_index` answered with the LAST JUMP in the stream. A merged
stream appends each inlined region after the owner's ops, so the last JUMP is a
region's, not the owner's. It now answers with the first.
That flip removes a decline the old behaviour produced by accident: a region
whose closing JUMP named another module's published LABEL resolved to no LABEL
in the merged stream, so `merged_stream_has_loop_label` was false and the region
was refused. The accept condition now states that requirement directly (diag 51,
`inline_decl_foreign_label`) — the emitter turns a region's JUMP into a `br`,
which cannot leave the module.
Also emit, behind `PYRE_WASM_INLINE_NONHEADER`, an in-module resume for a region
whose closing JUMP names a resumable LABEL other than the loop header. Such a
region cannot `br` to the `loop`, which opens at the header. Under
`resume_dispatch` the entry dispatch is wrapped in a `loop` the region branches
back into, and the entry `br_table` gains a second bucket per label: key
`num_labels + 1 + j` targets the block past label j's resume loader, so the
region passes its values in locals instead of through frame slots. Both
in-dispatch and in-loop branch depths gain one level. A module with no such
region takes none of it and is byte-identical.
The flag is opt-in: the shape is wasmparser-valid and correct on the unit-test
traces added here, but on real IR 47 check.py fixtures fail identically with a
corrupted Ref. `check.py --backend wasm` is 437/437 with the flag off.
Assisted-by: Claude
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Five commits on top of
origin/main; the last two are this cycle's work.The defect
With
PYRE_WASM_INLINE_BRIDGE=1, a Ref returned by a callee read asNonein the caller.CaParamsis decided when the owner loop is compiled, andreemit_loopreuses the owner's storedModuleBuildInputsverbatim while appending the region toinlined_bridges—inputs.cais never widened. So a region merged in later brings a callee that is absent fromca.targets.The dedicated arm is
opcode if opcode.is_call_assembler() && ca.emit_ca =>. A miss is not an error: the match falls through to the ordinary residual-call arm, which lowersop.arg(0)as an__indirect_function_tableslot. A CALL_ASSEMBLER's arg 0 is the callee's first frame slot, so the module called whatever that integer indexed and handed the result back as the callee's return value.wasm_unsupported_trace_reasonasks exactly this question of every trace's own ops before compiling it. The merged stream was the one place it was never re-asked.Evidence: the standalone bridge module (flag off, 8070 B) has
unreachable = 1, the CA arm's zero-dispatch trap; the merged module that swallowed it (flag on, 21534 B) hasunreachable = 0. At runtimePYRE_WASM_CALL_HIST=1showed one call atslot=10721072— a linear-memory object address — against legitimate slots of 5598-5697.The change
build_wasm_modulere-asks the question in the loop that validates the merged stream: anyis_call_assembler()op whosecall_target_token()is absent fromca.targets, or any such op at all when!ca.emit_ca, declines.classify_inline_install_errorfiles it asBRIDGE_DIAG[49]/inline_decl_call_assembler.Widening
caat merge time instead is a feature, not a fix: flippingemit_cachangesbase_i32_locals, the module type section and the residual helper arity family, andca_inline_params(ca_max_frame_bytes(targets))has to fit an already-frozen frame.The second commit makes the host trampoline name a call-area FUNC field that indexes no live function. It answered a
table.getmiss by writing 0 and returning Ok, and for a Ref result that 0 is indistinguishable from a null Ref the callee returned — which is what made this miscompile silent rather than a trap. The value written is unchanged.Verification
inlined_bridge_carrying_an_unarmed_call_assembler_declinescoversCallAssemblerIandCallAssemblerRunder bothCaParams::default()andemit_ca: truewith emptytargets, with an ordinary-opcode control that must still build. Mutation-tested: with the gate removed,build_wasm_modulereturnsOk— it builds the miscompiling module.cargo test -p majit-backend-wasm44/44.Guest runs, flag off vs on:
inline_okinline_decl_call_assemblerA 481383A 48138334285723428572The second row is the one that matters: the decline is targeted, and the shape that inlining actually helps still inlines. After the fix the
PYRE_WASM_CALL_HISThistograms are identical with the flag on and off.The trampoline diagnostic produces no output across 431
pyre/bench/synthand 15pyre/benchfixtures.The default path is untouched by construction: the new loop body only runs when
inlined_bridgesis non-empty, which requiresPYRE_WASM_INLINE_BRIDGE.Summary by CodeRabbit
Bug Fixes
Diagnostics