If we are pulling in stdbool.h and this is C11...that is undefined behavior and because it wasn't validly initialized it is an indeterminate-value read...which means for optimization that the compiler is within its right to assume it is a 0 or 1 and could test it in different ways depending on the surrounding code (nonzero test, compare to 1, etc).
On Wed, Sep 16, 2026 at 10:14 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> However, what I'm seeing as I trace through the crash on
> longfin is that nulls[19] has a value that's not either 0 or 1 (not
> too surprising), and somehow heap_compute_data_size is interpreting
> that as "true" while fill_val is reading it as "false". According
> to my understanding of the C standard, fill_val is in the wrong here.
Is the _Bool representation allowed to contain anything but zero/false
or one/true? I thought that was undefined behavior. (IIRC, mixing C++
bool with our C89-era bool definition suffered from similar UB
excitement.)
--Jacob
