IR overflow: a fixed MAX_IR node limit rejects very large (valid) functions

• Type: bug / scalability limit (Track A — compiler/ir.inc, defs.inc). A capacity limit, not a miscompile: pxx rejects a program FPC compiles, with error: IR overflow — it never emits wrong code.
• Status: done
• Found: 2026-07-17, pasmith non-interface high-complexity run (seed 60030, pxx-reject_overflow, 13 hits).

Cause

ir.inc:25: if IRCount >= MAX_IR then Error('IR overflow'). MAX_IR = 131072 (defs.inc:48) sizes the global IR arrays (IRKind/IRA/IRB/IRC/IRIVal/IRTk, each array[0..MAX_IR-1]). A single function body that lowers to > 131072 IR nodes overflows the array and is rejected. FPC has no such fixed cap.

The trigger here is pathological: pasmith's exit checksum hashes every element of every variable (14 scalars + 4×array + 4×record + strings + objects) into one main, so main alone exceeds 131072 nodes. Hand-written code rarely reaches this in one function — hence low priority — but a large generated/amalgamated function (or a huge case, a big unrolled initializer) legitimately can.

Status: cheap tier DONE, proper fix open

MAX_IR bumped 131072 → 262144 (5a067617) — seed 60030 now compiles and matches the FPC checksum (the cap was not hiding a miscompile), self-host byte-identical. The hard cap still exists at 2× — a large enough function still overflows. Ticket stays open for the dynamic-array proper fix; deprioritised (the wall just moved).

Fix direction

• Cheap, partial: bump MAX_IR (e.g. 131072 → 262144). Byte-identical-safe (the compiler's own bodies stay well under the cap, so self-host output is unchanged; only the array sizes — and global memory ~+6 MB — grow). Just moves the wall.
• Proper: make the IR arrays dynamic (grow on demand), removing the hard cap. Bigger change; touches every backend that indexes the IR arrays. Related scalability work: [[perf-c-parse-codegen-large-file-superlinear]].

Acceptance

• Seed 60030 compiles (or a hand-written function with > 131072 IR nodes does).
• Gate: make test + self-host byte-identical.

Note

Low severity — a capacity ceiling, no wrong code. Filed for the record; the pasmith trigger is an unusually large single function, not typical source.

Log

• 2026-07-18 — resolved, commit cf7bbcea.