https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108941
--- Comment #14 from jbeulich at suse dot com ---
(In reply to Jakub Jelinek from comment #5)
> GCC doesn't even have that information at all, at the RTL level it doesn't
> know
> if it was signed or unsigned.
> All it has is the constraint and operand for it, like (reg:QI 126) or
> (const_int -1).
Lack of information at a certain layer doesn't mean this isn't a bug. It merely
makes whatever possible bug one that's hard to fix.
Furthermore you did refer to gcc internal doc as to justifying the behavior.
But can you also point me at non-internal doc making explicit that e.g.
static inline unsigned aux(unsigned i, unsigned char j) {
#if 1
asm("add %1,%0" : "+rm" (i) : "i" (j));
return i;
#else
return i + j;
#endif
}
unsigned test(unsigned i, unsigned j) {
return aux(i, 255) * aux(j, -1);
}
does not do (at -O1 or -O2) what one would expect (again on x86)? The example
is intentionally over-simplified (and hence won't build at -O0); anything more
involved could be taken care of by using assembler macros, where it is not
overly difficult to separately deal with immediates and registers.
In the absence of such documentation I would also view the "has always been
like that" argument as at least questionable.
