perf: join the program lines as one sized copy #205
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Goal
The profile of the compiler's own build names
Iterate.joinedover the lines of the program (about 70 MB of C joined twice, pairwise in log n passes) at 4% of the build. Join the lines with one copy into a buffer of the right size, forprogram.cand per unit.Design record
PERFORMANCE.md 9.6 ("The compiler's own build"). Part of #144.
Acceptance criteria
windows-x64,linux-x64), five conformance programs andtools/release-sync(sh tools/agree.sh emithash lines equal tomain's, compared in CI).torb build --emit-c ./compileris faster in the alternating-run comparison (expected about 4%; if the gain is below noise, say so in PERFORMANCE.md and the PR stays only if the code is not more complex).sh tools/gates.sh ais green in forge CI.Measurement
Measured in CI, no local bootstrap: the forge CI job for the PR runs
sh tools/gates.sh a; the before/after processor times come fromtorb check tests/conformance/adts.trb,torb build --emit-c tests/conformance/adts.trbandtorb build --emit-c ./compilerrun with themainbinary and the PR binary alternating (3 runs, mean, as in PERFORMANCE.md 9.5), printed in the CI log and copied into PERFORMANCE.md 9.7. CI machines are noisy, so the ratio of alternating runs counts, not absolute seconds.Seed impact
None if the sized copy uses natives and std names that already exist in the seed. If it needs a new native or std member the seed does not have, stop and split with the two-commit rule of
CLAUDE.md(then it becomes an owner decision). One PR.[loop:torbscript] claim implement by session:loop-torbscript-20261008 until 2026-10-08T21:17Z
[loop:torbscript] release implement: the worker of the previous claim ended without a commit or a branch on the forge (its worktree is clean), so the claim is void; a new worker takes the issue below
[loop:torbscript] claim implement by session:loop-torbscript-20261008 until 2026-10-08T22:35Z
[loop:torbscript] release implement: seed impact - the sized copy needs a new native, so this becomes a two-commit change and the loop has to decide it; no commit, no PR, the branch
loop/205-sized-joinwas not pushed. usage: ~90k tokens / ~20 min. next: waiting (decision on the native, two-commit rule of CLAUDE.md)What I found (on
main6374a3f0):emittedText(compiler/src/backend/c/emission.trb:152) andtextOf(compiler/src/backend/c/units.trb:224), bothlines.joined(separator: "\n") + "\n", which isconcatenatedinstd/iteration/src/concatenate.trb: pairwise merges,log nlevels.Stringof a size known only at run time in one copy:Intrinsic.TextConcat(torb_text_concat/torb_text_concat_parts) takes a fixed number of parts, the number the interpolation was written with.Stringin one copy:String.copyBytesgoes the other way,torb_text_try_from_bytesis only reachable through IO natives (File.readText, ...), andtextOfinstd/streamdecodes character by character.String.repeat,replace,split,sliceBytesand+cannot fill a buffer from a list either.Stringitself (File.writeText,units.header.hash(),torb run's cache key, the fixpoint), so writing the lines straight to the file would be a scope change.Options:
concatenated(pieces, separator)answered by the runtime (torb_text_join: measure, allocate once, copy once) in the C back end and in the VM. Under the two-commit rule: commit 1 teaches the native (withconcatenatedkeeping its TorbScript body for the seed), seed refresh by the owner, then commit 2 uses it inemittedTextandtextOf. Sinceconcatenatedis a std function, the C of every program that joins text changes, so the "emitted C byte-identical" criterion would hold only if the compiler keeps its own join incompiler/src/backend/cand that is the only caller that changes."{a}{s}{b}{s}...", which is oneTextConcat, one allocation). That makeslog16 nlevels (about 6 for ~1.7 M lines) instead oflog2 n(about 21), so about 3-4x fewer bytes copied, but it is not one copy, and a 16-part interpolation is more code than the current loop. Expected gain: most of the 4%, unmeasured.I did not start option 2 because the brief said to stop on seed impact rather than change the design of the issue.
[loop:torbscript] decided by the loop: performance work and measurable, so measured first, not asked. Option 2 (no native) goes first: merge 16 pieces per level through one fixed-arity interpolation (one
TextConcat, one allocation) in the compiler's own join inemittedTextandtextOf, so no seed step, one PR, emitted C byte-identical. Reasoning: it needs no seed refresh (that stays the owner's) and its gain is measured in forge CI againstmain(alternating runs, PERFORMANCE.md 9.7). If the measured gain stays well below the expected ~4%, a follow-up issue files option 1 (torb_text_joinnative under the two-commit rule) with the numbers. Next: implement.[loop:torbscript] claim implement by session:loop-torbscript-20261008 until 2026-10-08T22:40Z
[loop:torbscript] implement: PR #213 (branch
loop/205-sized-join, head94c6b473) is open with option 2 as decided (linesTextin the C back end, 16-way merges, no native, no seed step); the worker session ended before it read the forge CI result. CI on the PR is running (bootstrap linux-x64 green, gates and tier A/B pending). Red CI on the PR starts a fix round. Worker usage: not reported (session lost). next: waiting (forge CI on PR #213)[loop:torbscript] review: the merge gate asked for a boundary test of
linesTextand the numbers in PERFORMANCE.md; both are in head41dacca2on PR #213 (committest(compiler): pin linesText at its edges, record the numbers in PERFORMANCE.md 9.8), review re-requested, CI running. next: waiting (merge gate review on PR #213)[loop:torbscript] claim review by session:loop-torbscript-20261008 until 2026-10-08T20:08Z
[loop:torbscript] release review: PR #213 is red at
41dacca2on one gate only,format --check(compiler/tests/lines-text.test.trbwould be reformatted; every other gate was green). The fix worker could not be spawned (model account unavailable at the gateway). next: waiting (fix round: format the test file, retry when a worker model is available)