Brummel
4cacfcbdac
Hypothesis-driven measurement of "did monomorphisation actually buy us performance?" on a 100M-iter LCG hot loop, AILang mono'd code vs. four C reference variants (direct-inlinable, direct- noinline, indirect-monomorphic, indirect-polymorphic). Zen 3, clang -O2, median-of-15. Headline: H1 supported, but the mechanism is inlining, not dispatch shape. AILang mono = hand-C direct (1.000x). Indirect- monomorphic = direct-noinline (1.000x) — saturating branch predictor makes the indirect-call cost vanish on this hardware. Inlining is the actual 3.31x win; polymorphic indirect adds another 21% predictor-miss penalty. DESIGN.md Decision 11 gains a rationale paragraph reframing mono as inlining-enabler rather than indirect-call-eliminator, with explicit pointer to the bench. JOURNAL entry records the full methodology, ratios, limitations, and the side-effect mono-pass env.globals-seeding bug surfaced while building the AILang fixture (separate RED-first debug iter to follow).
40 lines
1.1 KiB
C
40 lines
1.1 KiB
C
// Hand-C reference for bench_mono_dispatch — DIRECT, INLINABLE variant.
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//
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// Mirrors the post-monomorphisation AILang IR: a tail-recursive loop
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// that calls `foo(i)` at every step. `foo` here has no `noinline`
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// attribute, so clang -O2 will inline it into the loop body. This is
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// the OPTIMISTIC bound on what AILang's mono pass can achieve once
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// LLVM optimises the resulting IR.
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//
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// Workload: loop_call(N, 0) with
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// acc' = acc + foo(acc + i)
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// foo(x) = x * 1103515245 + 12345 (LCG-ish, prevents closed-form)
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//
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// N = 100_000_000.
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//
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// The result is data-dependent on every prior iteration, so clang
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// cannot algebraically close-form-fold the loop; the wall-time is
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// dominated by the body.
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//
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// Build: clang -O2 -o bench_mono_direct bench_mono_direct.c
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#include <stdio.h>
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#include <stdint.h>
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static int64_t foo(int64_t x) {
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return x * 1103515245 + 12345;
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}
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static int64_t loop_call(int64_t i, int64_t acc) {
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while (i != 0) {
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acc = acc + foo(acc + i);
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i = i - 1;
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}
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return acc;
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}
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int main(void) {
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printf("%lld\n", (long long)loop_call(100000000, 0));
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return 0;
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}
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