Fix -Wmaybe-uninitialized warning in js_binary_logic_slow#1530
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GCC (observed with 16.1) cannot prove that buf2 is initialized on the
BigInt shift path: js_bigint_get_si_sat(p2) is inlined and reads
buf2.tab via js_bigint_sign(), but GCC loses track of the preceding
js_bigint_set_short(&buf2, op2) store. The read is in fact always safe.
A declaration initializer (JSBigIntBuf buf2 = {0};) does not help because
the slow_big_int: label is reachable via goto, which jumps over the
initializer. Zero-initialize buf2 with memset() just after the label so it
runs on every entry path.
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Fix -Wmaybe-uninitialized warning in js_binary_logic_slow (quickjs.c).
GCC (seen with 16.1.1, Release/-O2) warns that buf2 may be used
uninitialized on the BigInt logic/shift path. js_bigint_get_si_sat(p2)
is inlined and reads buf2.tab via js_bigint_sign(), and GCC can't
correlate that with the earlier js_bigint_set_short(&buf2, op2) store.
The read is in fact always safe.
A declaration initializer (JSBigIntBuf buf2 = {0};) does not help,
because the slow_big_int: label is reached via goto, which jumps over
the initializer. The fix zero-initializes buf2 with memset() right
after the label so it runs on every entry path.
Verified on master with GCC 16.1.1: warning gone, tests.conf suite
passes (0/63 errors), api-test passes, and BigInt ops are correct
(123n<<4n=1968, -5n>>1n=-3, 6n&3n=2).
buf1 in the same function could be initialized the same way for
symmetry, though it does not currently trigger a warning. Happy to add
that if preferred.
Disclosure: prepared with AI assistance. I reviewed the code path,
reproduced the warning on master, verified the fix, and ran the test
suite myself.