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Inline expansion — remaining slices (branch-with-locals + non-leaf)

What shipped already (context — do not redo)

feature-inline-routines delivered, all at -O2, all gated OptLevel>=2, -O0/-O1 byte-identical, validated O0-vs-O2 across ~700 programs + 4 cross targets:

The retention/splice machinery (TryRetainInlineBody / TryRetainInlineStmtBody in parser.inc; IRInlineExpand / IRCloneInlineBody in ir.inc; the reserved AST region + placeholders) is the reusable base for everything below.

Slice 2c — if-then-else with locals / multiple statements per branch

2b is straight-line only (rejects any AN_IF in a multi-statement body). The common next shape is a body that branches AND uses locals, e.g.

function Clamp(v, lo, hi: Integer): Integer; inline;
begin
  Result := v;
  if Result < lo then Result := lo;
  if Result > hi then Result := hi;
end;

Blockers to solve:

Slice 4 — non-leaf inlining (under a depth budget)

Drop the leaf-only rule: inline bodies that themselves call. The ~97% of call sites 2b/2c can't reach. Needs (see the design notes in [[feature-inline-routines]] "slice 4" section):

Acceptance (per slice)

Log

2026-09-05 (frank-optimize) — the depth budget lifted; the REACH is the finding

Two slices remained: while/for bodies, and depth>1 non-leaf. Measured the bound on each before writing any code, because the choice between them is an empirical question and the census-of-opportunity answer would have been wrong.

remaining slice current -O3 hand-inlined bound
while/for body (SumTo(3) in a hot loop) 0.26s 0.19s 1.37x
depth>1 non-leaf (Top -> Mid -> Leaf) 0.53s 0.17s 3.12x

SumTo declines today (PXXDBG=a.inline shows no retention), confirming the loop-body slice is unimplemented rather than merely unprofitable.

Isolated the mechanism instead of inferring it. Hand-inlining ONLY Leaf into Mid — leaving the Top->Mid chain to the compiler — gave 0.16s against 0.46s. So one additional depth level is worth 2.87x of the 3.29x total, and the budget is the cost rather than anything else in the pass.

The change

InliningActive < 2 in the AN_CALL gate was a bare literal permitting one re-inline level. It is now MAX_INLINE_DEPTH (defs.inc) = 3. The constant is the termination proof, not a tuning knob: there is no recursion guard by proc identity, so a self-recursive chain stops only because the budget is spent. RecSum in the new test exists to keep that honest.

Delivered, and the reach is narrow

EVERY NUMBER IN THIS SECTION WAS TAKEN UNDER LOAD 12.9-15.2 (fleet gating; frankC, frankS and frankH all building). That is the contaminated regime, not the clean one, and this ticket's own calibration pair from the record half says which way it errs: the same kind of ratio read 1.543x unloaded and 1.665x at load 16-19, ~8% inflated, because the call-heavy control loses more to contention than the inlined arm does. So 1.92x and 1.13x are upper estimates and both need a re-take on a quiet box before they are quoted as delivered. Recording them with their conditions rather than discarding them: the pair above is enough to calibrate, and the byte-identical results (12 of 13 programs, compiler.pas at every level) are load-INDEPENDENT and stand as measured.

The 12-of-13 is the honest headline, not the 1.92x. The extra level needs a three-deep chain of mutually-retained bodies, and that conjunction is rare: 170 procs retain in compiler.pas and 60 of those have calls, yet the depth change alters nothing there. Checked FrameIntrinsicUsed first as the candidate explanation and it is NOT the cause — no frame intrinsic is called in compiler.pas (the grep hits are the parser recognising the names).

So this is a narrow win at an opt-in level, not a general one. It is recorded that way so nobody reads 1.92x as what a program will get.

Not proven

test_inline_depth2.pas added and wired into the -O3 sweep block. Its expected values are FPC 3.2.2's (verified by compiling and running it under FPC), per that block's own standard. It asserts side-effect COUNT and ORDER through two splice levels, not values alone — a value check cannot see an argument evaluated twice when the second evaluation yields the same number. Confirmed the test is AIMED: the emitted binary differs between the old and new compilers, so its program actually reaches the new path.

Also corrected test_inline_nonleaf.pas's header, which still claimed inner calls stay real calls — untrue since d4c19919 re-landed depth-1.

REMAINING: while/for loop bodies (bound 1.37x, measured above).

2026-09-05 — REACH measured before implementing the while/for slice

The depth slice was chosen on the bigger BOUND (3.12x vs 1.37x) and delivered the smaller result: 12 of 13 real programs byte-identical. That is the measurement establishing the principle, so the remaining slice gets its reach counted FIRST, before any code.

Added PXXDBG=a.inlinedecline (inert unless enabled; compiler.pas byte- identical at -O0/-O2/-O3 with and without it): which statement kind stopped a body that had ALREADY cleared the locals and Result gates.

Across 13 example programs + compiler.pas — distinct function names, because the RTL is recompiled into every program and inflates a raw count (StrLCopy appears 24 times, StrLComp and StrIComp 12 each):

blocking statement distinct functions
while 102
bare call statement (AN_CALL) 67
for 32
case 19
repeat / asm 1 each

135 distinct functions are blocked solely by a loop statement, against the depth slice's one affected program in thirteen. Reach favours while/for by two orders of magnitude even though its ceiling is less than half.

135 IS AN UPPER BOUND AND PROBABLY A LOOSE ONE. These bodies cleared the locals/Result gates and hit a loop; accepting loops does not make them inline. The binding constraint will be definite assignment: for i := 1 to n do Result := ... does NOT definitely assign Result, because the loop may run zero times, and the same applies to every while. How much of the 135 survives that cannot be known without implementing the analysis, so this number sizes the OPPORTUNITY and must not be quoted as delivery — the distinction this ticket already got wrong once.

A measurement fault worth recording, caught by frank-coordinator's caution that zero and unmeasurable must not both print 0: the first census printed life 2. life does not compile here at all (rc=1, no binary — the GTK3 headers resolve to GTK2; identical on all three compilers, so not a regression), and the 2 was partial output emitted before the error. The re-run guards on rc AND on the binary existing, and prints UNMEASURABLE. sudoku's 0 is genuine — it compiles and has no declines at all. The depth census in the section above was NOT affected: it guarded compiles with || continue, life is absent from its thirteen, and built=13 is consistent with that.

A shape no ticket names

67 distinct functions decline on a bare procedure-call statement in the body — the second-largest blocker, larger than for, and not in this ticket's remaining scope nor anywhere else. Filed as [[feature-opt-inline-bodies-with-a-statement-level-call]].

2026-09-05 — CALL-SITE FREQUENCY MEASURED. The admission axis is saturated.

I wrote that nobody should pick another slice by a static metric before someone measured call-site frequency. That measurement was available the whole time and neither I nor the coordinator looked: perf is denied here (kernel.perf_event_paranoid = 4), but compiler.pas is FPC-bootstrappable and FPC supports -pg — the playbook has said so under "perf being blocked is not 'no profiler'" for some time. Eleven seconds to build, and gprof -b -p prints call counts that are properties of the SOURCE and exactly ours (the time shares are FPC's codegen and only indicative; the counts are not).

Workload: the -pg compiler compiling examples/raytracer/raytracer.pas at -O3.

calls share
total attributed 9,507,756
to functions the inliner already retains 1,235,476 13.0%
to functions it declines on statement kind 106,690 1.12%

118 of the 156 declined functions are called ZERO times. Three quarters of the remaining "opportunity" is code that does not execute at all in a real compile.

And the 1.12% is concentrated, not spread:

TYPESLOTSIZE          case    39,995
RESIDENTREGOF         for     38,847
BUILTINRECFIELDCOUNT  case     6,053
FLOATRESIDENTXMMOF    for      4,283
DCENEWOFF             while    3,277

The top two are 79k of the 107k — 0.4% of all calls each.

What this decides

Admitting every remaining statement shape would touch ~1% of executed calls, and inlining does not make a call free, so the realisable gain is a fraction of that. The inliner already covers the functions taking 13% of calls. The axis is saturated and the remaining slices are not worth their risk — this ticket's own history is a revert after 21 silent divergences, which is the price of being wrong in this machinery.

This retires all three static metrics, mine included. Bound picked depth>1 (changed 1 program of 13). Reach picked statement-calls (changed 0 of 16). Frequency now says why both failed: they counted shapes a validator could admit, and the shapes it cannot admit are overwhelmingly cold.

THE AXIS WAS NEVER BOUND-VS-REACH. IT IS STATIC-VS-EXECUTED, and both of my earlier positions were on the wrong side of it. I corrected myself once, from "biggest bound" to "biggest reach", and that correction was still a static metric and still wrong. Stated this way because the failure mode is picking a FOURTH static metric — most-call-sites-in-source, most-lines, most-parameters — and finding it also predicts nothing. A count of source shapes cannot predict delivered value no matter how the count is refined. The only metric that predicted anything was a count of what actually ran.

If anyone does pursue this, the answer is not "support case and for" — it is TypeSlotSize and ResidentRegOf specifically, two functions worth 0.4% of calls each, and the honest first question is whether either is better served by not being a function call at all.

REMAINING SCOPE OF THIS TICKET IS THEREFORE CLOSED ON VALUE, NOT ON DIFFICULTY. while/for bodies remain unimplemented and that is now a deliberate decision with a number behind it rather than an unfinished task.