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 12:34 PM Jacob Champion < [email protected]> wrote: > On Wed, Sep 16, 2026 at 10:14 AM Tom Lane <[email protected]> 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 > > >
