The per-test loop in main() spans the setjmp(g_test_jmp)/longjmp recovery
target: i is read (loop test + increment) on the longjmp-return path. gcc's
-Wclobbered (enabled under -Wall) flags exactly this loop-index-across-setjmp
shape. The build was clean today only coincidentally — the preceding qsort()
call biases gcc's register heuristic; an identical loop without it warns at
-O1/-O2 (verified). Qualify i as volatile per C11 7.13.2.1, the sanctioned
remedy (no pragma, no flag downgrade), with no behavior change. This is the
compile-cleanliness gate for the guard (parent bf-22vg).
Verified: gcc -std=c11 -Wall -Wextra -Wclobbered -Werror is clean at
-O0/-O1/-O2/-O3/-Os/-Og; make -C firmware/test test builds warning-free and
runs all 30 tests (exit 0). Only firmware/test/test_runner.c touched.
Co-Authored-By: Claude <noreply@anthropic.com>
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