From: Segher Boessenkool

Sent: 20 January 2023 10:54

...

quoted

quoted

I suggest to file a bug against gcc complaining about a "spurious
warning", and using "-Werror -Wno-error-sizeof-pointer-div" until gcc is
adapted to not emit the warning about the pointer division if the result
is not used.

Yeah.  If the first operand of a conditional operator is non-zero, the
second operand is not evaluated, and if the first is zero, the third
operand is not evaluated.  It is better if we do not warn about
something we do not evaluate.  In cases like here where it is clear at
compile time which branch is taken, that shouldn't be too hard.

Can someone please file a GCC PR?  With reduced testcase preferably.

It's not a bug.
All the operands of the conditional operator have to be valid.
It might be that the optimiser can discard one, but that happens
much later on.
Even the operands of choose_expr() have to be valid - but can
have different types.

I'm not sure what the code is trying to do or why it is failing.
Was it a fail in userspace - where the option to allow sizeof (void)
isn't allowed.

FWIW you can check for a compile-time NULL (or 0) with:
#define is_null(x) (sizeof *(0 : (void *)(x) ? (int *)0) != 1)

Although that is a compile-time error for non-NULL unless
'void *' arithmetic is allowed.

	David

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