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feat(vcr-ra): i64 pair-spill via param frame-backing — VCR-RA-001 acceptance closes (v0.11.40) #325

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Merged
avrabe merged 1 commit into from
Jun 11, 2026
Merged

feat(vcr-ra): i64 pair-spill via param frame-backing — VCR-RA-001 acceptance closes (v0.11.40) #325

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113 changes: 64 additions & 49 deletions crates/synth-backend/src/arm_backend.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -160,57 +160,72 @@ fn compile_wasm_to_arm(
// unmodified default, so every function that compiles today is selected by
// exactly the code that compiled it yesterday (bit-identity is structural,
// not behavioural).
let select_direct_attempt =
|spill_on_exhaustion: bool| -> Result<Vec<ArmInstruction>, synth_core::Error> {
let db = RuleDatabase::with_standard_rules();
let mut selector =
InstructionSelector::with_bounds_check(db.rules().to_vec(), bounds_config);
selector.set_target(config.target.fpu, &config.target.triple);
if config.num_imports > 0 {
selector.set_num_imports(config.num_imports);
}
// #195: plumb the callee argument-count tables so the direct selector can
// marshal call arguments into R0–R3 per AAPCS.
selector.set_func_arg_counts(
config.func_arg_counts.clone(),
config.type_arg_counts.clone(),
);
// #197: in relocatable host-link mode, emit direct `func_N` BLs for
// imports (rewritten to the wasm field name by build_relocatable_elf)
// instead of `__meld_dispatch_import`.
selector.set_relocatable(config.relocatable);
// #237: native-pointer ABI — wasm statics become __synth_wasm_data-relative.
selector.set_native_pointer_abi(config.native_pointer_abi, config.linear_memory_bytes);
// #311: i64 call results are register PAIRS — tag them.
selector.set_result_types(config.func_ret_i64.clone(), config.type_ret_i64.clone());
// Stack-pointer promotion is meaningful only under the native-pointer ABI;
// gating here keeps every non-native compile (all frozen fixtures) on the
// legacy R9 globals-table path, bit-identical.
if config.native_pointer_abi
&& let Some((sp_idx, sp_init)) = config.stack_pointer_global
{
selector.set_native_pointer_stack(sp_idx, sp_init);
}
selector.set_spill_on_exhaustion(spill_on_exhaustion);
selector.select_with_stack(wasm_ops, num_params)
};
let select_direct_attempt = |spill_on_exhaustion: bool,
param_backing_on_exhaustion: bool|
-> Result<Vec<ArmInstruction>, synth_core::Error> {
let db = RuleDatabase::with_standard_rules();
let mut selector =
InstructionSelector::with_bounds_check(db.rules().to_vec(), bounds_config);
selector.set_target(config.target.fpu, &config.target.triple);
if config.num_imports > 0 {
selector.set_num_imports(config.num_imports);
}
// #195: plumb the callee argument-count tables so the direct selector can
// marshal call arguments into R0–R3 per AAPCS.
selector.set_func_arg_counts(
config.func_arg_counts.clone(),
config.type_arg_counts.clone(),
);
// #197: in relocatable host-link mode, emit direct `func_N` BLs for
// imports (rewritten to the wasm field name by build_relocatable_elf)
// instead of `__meld_dispatch_import`.
selector.set_relocatable(config.relocatable);
// #237: native-pointer ABI — wasm statics become __synth_wasm_data-relative.
selector.set_native_pointer_abi(config.native_pointer_abi, config.linear_memory_bytes);
// #311: i64 call results are register PAIRS — tag them.
selector.set_result_types(config.func_ret_i64.clone(), config.type_ret_i64.clone());
// Stack-pointer promotion is meaningful only under the native-pointer ABI;
// gating here keeps every non-native compile (all frozen fixtures) on the
// legacy R9 globals-table path, bit-identical.
if config.native_pointer_abi
&& let Some((sp_idx, sp_init)) = config.stack_pointer_global
{
selector.set_native_pointer_stack(sp_idx, sp_init);
}
selector.set_spill_on_exhaustion(spill_on_exhaustion);
selector.set_param_backing_on_exhaustion(param_backing_on_exhaustion);
selector.select_with_stack(wasm_ops, num_params)
};
let select_direct = || -> Result<Vec<ArmInstruction>, String> {
match select_direct_attempt(false) {
Ok(instrs) => Ok(instrs),
// VCR-RA-001 step 3b-lite (#242): the i32 register-exhaustion
// hard-fail is recoverable — retry once with spill-on-exhaustion,
// which reserves the spill area and spills the deepest stack value
// when the pool is full. Only functions that FAILED the first pass
// ever reach this, so existing output is untouched by construction.
Err(e)
if e.to_string()
.contains("all allocatable registers are live on the stack") =>
{
select_direct_attempt(true)
.map_err(|e| format!("instruction selection failed: {}", e))
}
Err(e) => Err(format!("instruction selection failed: {}", e)),
// The two recoverable exhaustion classes. NOT retried: the i64
// spill-slot-pool Err ("spill-slot pool exhausted") — the honest
// remaining bound of the 3b-lite allocator.
const SINGLE_EXHAUSTION: &str = "all allocatable registers are live on the stack";
const PAIR_EXHAUSTION: &str = "no consecutive pair of free registers for i64";
let mut attempt = select_direct_attempt(false, false);
// VCR-RA-001 step 3b-lite (#242): the i32 register-exhaustion
// hard-fail is recoverable — retry with spill-on-exhaustion, which
// reserves the spill area and spills the deepest stack value when the
// pool is full. Only functions that FAILED the first pass ever reach
// this, so existing output is untouched by construction.
if let Err(e) = &attempt
&& e.to_string().contains(SINGLE_EXHAUSTION)
{
attempt = select_direct_attempt(true, false);
}
// VCR-RA-001 acceptance increment (#242): the i64 consecutive-PAIR
// exhaustion is recoverable too — but not by stack spilling (the pair
// allocator already spills stack values, #171): the blockers are the
// pinned param home registers. The final retry frame-backs the params
// (#204 machinery) so they stop pinning R0-R3, with spill-on-exhaustion
// kept on for the single-register pressure the reloads add. Reached
// only by functions that failed every earlier pass.
if let Err(e) = &attempt
&& e.to_string().contains(PAIR_EXHAUSTION)
{
attempt = select_direct_attempt(true, true);
}
attempt.map_err(|e| format!("instruction selection failed: {}", e))
};

// Instruction selection: optimized or direct.
Expand Down
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