perf(codegen): preserve_none calling convention for recursion-participating spec clones (#8175) - #8203
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📝 WalkthroughWalkthroughThe change applies LLVM ChangesRecursive specialized clone calling convention
Estimated code review effort: 4 (Complex) | ~45 minutes Merge Risk: 🟡 Moderate · up to The new calling convention is currently enabled for ARM64 MinGW targets that are supposed to be excluded, creating a platform-specific build or runtime correctness risk. The target gate should reject ARM64 MinGW while retaining supported x86-64 MinGW behavior before merge. Sequence Diagram(s)sequenceDiagram
participant HIR
participant SpecializedABI
participant LlModule
participant LLVMIR
HIR->>SpecializedABI: identify recursive specialized functions
SpecializedABI->>LlModule: register eligible clone symbols
LlModule->>LLVMIR: emit preserve_nonecc definitions and declarations
LlModule->>LLVMIR: emit preserve_nonecc calls and invokes
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In `@crates/perry-codegen/src/codegen/spec_abi.rs`:
- Around line 90-96: Update preserve_none_target_ok so any target containing
“mingw” is rejected unless it is an accepted x86_64 target, thereby rejecting
aarch64-w64-mingw32 while preserving x86_64 MinGW acceptance. Add regression
coverage for both ARM64 MinGW rejection and x86_64 MinGW acceptance.
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changelog.d/8203-spec-preserve-none.mdcrates/perry-codegen/src/block.rscrates/perry-codegen/src/codegen/mod.rscrates/perry-codegen/src/codegen/spec_abi.rscrates/perry-codegen/src/codegen/spec_preserve_none_tests.rscrates/perry-codegen/src/codegen/spec_self_recursion_tests.rscrates/perry-codegen/src/collectors/hot_callees.rscrates/perry-codegen/src/collectors/mod.rscrates/perry-codegen/src/dialect/eh.rscrates/perry-codegen/src/dialect/mod.rscrates/perry-codegen/src/dialect/tests.rscrates/perry-codegen/src/function.rscrates/perry-codegen/src/inst.rscrates/perry-codegen/src/module.rscrates/perry/src/commands/compile/build_cache.rscrates/perry/src/commands/compile/object_cache.rs
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…_none (#8175) With no callee-saved registers there is nothing for a param-derived live-across-call value to pin in the entry block, so LLVM shrink-wrapping sinks the whole frame into the recursive path and the leaf runs frameless. - one registry (LlModule -> RegCounter) drives define header, declare line, and both call choke points (call + invoke arm), so a call site can never disagree with its callee's convention - gated to recursion participants (Tarjan SCC over direct FuncRef edges): the ~20-CSR boundary prologue amortizes only under a recursive tree - target-gated off watchOS arm64_32 and ARM64 Windows, same predicate family as the RS4GC target-awareness - PERRY_SPEC_PRESERVE_NONE=0 kill switch, keyed into build+object caches - dialect reader parses the token on define/call/invoke and sets the real LLVM convention (PreserveNone=21) on both fn and call sites - liveness gates: define+call-site agreement scanned module-wide, and an asm-level assert that the clone's entry is shrink-wrapped frameless Claude-Session: https://claude.ai/code/session_01AHvBYz7E6wWKv8kmvLLGpj
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Merging. I measured this rather than taking the claim, because Measured on the quiet M1 mini, under
|
| arm | wall | spread |
|---|---|---|
main @ 14468dcbc |
0.7597 s | 0.1% |
| this PR | 0.3419 s | 0.2% |
−55.0% wall, −21.4% instructions retired (4.668 B → 3.671 B). The main arm reproduces the sweep's 0.7619 s to within 0.3%, so the baseline is validated rather than assumed.
This does more than recover the regression
fib40's history is 0.3934 s (601a02d23, 08-14) → 10.5587 s (38cf15336, 08-15, when guarded ordinary-parameter specialization landed) → 0.7619 s (current main). At 0.3419 s this PR lands below the pre-regression baseline, and takes the row back outright:
| engine | fib40 |
|---|---|
| Perry + #8203 | 0.3419 |
| Porffor | 0.5133 |
| Perry (main) | 0.7597 |
| scriptc | 0.7900 |
| Node | 1.0361 |
Perry had lost this row to Porffor. It now wins it by 1.5×.
Note on the mechanism
Wall improved 55% while instructions improved 21%. That asymmetry is #8175's thesis confirmed: the cost was the callee-saved frame LLVM could not shrink-wrap away, so the win is prologue/epilogue and spill traffic rather than executed work. Worth keeping in mind for #8289 — instruction count alone would have under-predicted this.
Scoping the convention to recursion participants only, via Tarjan over direct FuncRef edges, is the right call — non-recursive clones keep the default convention and avoid preserve_none's caller-boundary cost.
Verification
perry-codegen --no-fail-fast 28 suites, 1521 passed, 9 failed — all nine in the known baseline. perry-runtime --lib 2568/0/4. cargo fmt, check_file_size, check_gc_env_knobs, unrooted_local_shape --check, gc_runtime_root_holders, check_thread_locals, addr_class_inventory all clean.
Closes #8175.
#8203 gives recursion-participating clones the preserve_none calling convention, which lands between `define internal`/`call` and the return type. The matchers here pinned a fixed prefix and stopped matching. Claude-Session: https://claude.ai/code/session_01AHvBYz7E6wWKv8kmvLLGpj
* perf(codegen): re-enter guarded specialization clones (#8169) * docs(changelog): key fragment to PR #8290 * test(codegen): tolerate preserve_nonecc in the spec-clone IR matchers #8203 gives recursion-participating clones the preserve_none calling convention, which lands between `define internal`/`call` and the return type. The matchers here pinned a fixed prefix and stopped matching. Claude-Session: https://claude.ai/code/session_01AHvBYz7E6wWKv8kmvLLGpj --------- Co-authored-by: Ralph Kuepper <ralph@skelpo.com>
1 participant
Fixes #8175.
Specialized clones that participate in direct recursion now use LLVM's
preserve_nonecalling convention. This removes the callee-saved-register frame that LLVM could not shrink-wrap away from fib40's leaf path.Implementation
FuncRefedges.preserve_nonecc; non-recursive clones keep the default convention and avoid its caller-boundary cost.force_externalcodegen-unit promotion.arm64_32and Windows ARM64 targets off. Supported AArch64 and x86-64 targets remain on.PERRY_SPEC_PRESERVE_NONE=0as a single-binary A/B switch and keys it into both build and object caches.Performance
Best-of-5 on the current M1 host, with both binaries produced by the same compiler and the control selected only through
PERRY_SPEC_PRESERVE_NONE=0:preserve_noneThe host was heavily contended during this run, so wall time is intentionally omitted; retired instructions, cycles, and user CPU time show the delivered change without claiming a noisy wall-clock number. The earlier 19-program corpus scope check found 16 byte-identical programs; only fib40, interp, and iso_miss changed.
Validation
cargo test -p perry-codegen --lib --no-fail-fast: 1,078 passed.invoke preserve_noneccin a protected region.cargo fmt --all -- --check,git diff --check, file-size policy, environment-knob drift, workspace architecture, and test-registration checks pass.No version bump: package manifests and lockfiles are unchanged. This PR adds only the required changelog fragment.
Summary by CodeRabbit
Performance
Configuration
PERRY_SPEC_PRESERVE_NONEsetting to enable or disable this optimization.Reliability