size_t arithmetic loses its width or its signedness

int a; double b; int i = -8;
-1 < sizeof(int)        /* i386/arm32/riscv32: pxx 1, gcc 0 */
i / sizeof(int)         /* ILP32: pxx -2, gcc 1073741822 */
sizeof a - sizeof b     /* x86-64/aarch64: pxx 4294967292, gcc 18446744073709551612 */

Found by the cross-target differential over test/c*.c (pxx --target=T under qemu against gcc -m32 for ILP32 and gcc for LP64), 2026-09-27.

Resolution (2026-09-28)

The sizeof result kind is size_t's for the target: tyUInt32 when TARGET_PTR_SIZE is 4, tyUInt64 otherwise (compiler/cparser.inc, the sizeof node). Fixture test/c_size_t_arithmetic_keeps_width_and_sign.c (16 rows, C truths in SIZE_MAX, one .expected for all five targets): v445 answers 4 to 6 rows wrong on each target, this build none.