perf(codegen): a loop region whose body calls out takes no array it only reads element values from

[proggeramlug]

Fixes the #10594 userplain and #10510 date_getTime regressions that #11790 introduced.

Cause

#11790 (#10741) makes an array a loop-region candidate when it is read at a static index (x & c) in any context. const d = ds[i & 63]; a += d.valueOf() therefore became a region loop over ds. The region was versioned, and the body triplicated (425 to 1,882 IR lines), to save one guarded element load per iteration. The method call in the body sets the region's dirty flag, so every iteration re-checks the guard. Both rows went from 151/158 to 167/176 instructions per op.

Fix

In a body that calls out (a call, new, a native method call), an array becomes a candidate only when the region serves it there: the body stores into it, or a Number consumer takes one of its reads (the dense raw-f64 facts). A call-free body keeps every proven-index read as before. There the facts hold across iterations, and the matrix's varying cells (const o = objs[k & 7]; o.d = k; h += o.a) depend on it. Static-index value reads still ride along once some other access makes the array a candidate.

Results (instructions per op)

row	morning	main	this PR
#10594 userplain	151	167	149
#10510 date_getTime	158	176	158

Real workloads (n=5, median instructions:u; main = 5b06d69)

workload	main instr	this PR	delta	full GCs main/PR	RSS KB main/PR	binary bytes main/PR
tsc (transpile x3)	185,061,848,135	184,882,479,994	-0.10%	247/244	323,232/325,372	182,782,336/182,782,336
zod x5000	19,830,425,976	19,828,116,479	-0.01%	0/0	59,088/59,420	24,440,056/24,440,056
qs parse_nested	32,987,388,575	32,988,301,059	+0.00%	0/0	60,064/60,544	27,301,072/27,301,072
commander parse_argv	8,912,043,876	8,911,944,007	-0.00%	0/0	57,240/57,564	34,203,080/34,203,080

Outputs are identical to main's in every run.

Verification

• New codegen test an_array_only_read_for_element_values_is_not_a_region_array. Its controls show that a Number-consumed masked read, and a value read in a call-free body, still make the array a region array. All region_array_loop_tests and region_loop_tests pass.
• perry-codegen (all) passed. Gap suite (1254 files) compared with main: 0 regressions. fmt: clean.
• Matrix (583 cells), all PRs of this lane combined against main: 3 cells +1..+4 instructions, 36 better. The varying cells are unchanged.

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⚙️ Run configuration

• Configuration used: defaults
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• Run ID: 943f26d4-9563-4144-ae7f-20734b067800

📥 Commits

Reviewing files that changed from the base of the PR and between e9575d8 and 6e21910.

📒 Files selected for processing (3)

• changelog.d/PENDING-regfix-region-value-reads.md
• crates/perry-codegen/src/expr/region_array_loop_tests.rs
• crates/perry-codegen/src/stmt/region_loop/arrays.rs

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