https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99540
Alex Coplan <acoplan at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |acoplan at gcc dot gnu.org
--- Comment #2 from Alex Coplan <acoplan at gcc dot gnu.org> ---
So aarch64_add_offset has:
/* Base the factor on LOW_BIT if we can calculate LOW_BIT
directly, since that should increase the chances of being
able to use a shift and add sequence. If LOW_BIT itself
is out of range, just use CNTD. */
if (low_bit <= 16 * 8)
factor /= low_bit;
else
low_bit = 1;
val = gen_int_mode (poly_int64 (low_bit * 2, low_bit * 2), mode);
val = aarch64_force_temporary (mode, temp1, val);
if (can_create_pseudo_p ())
{
rtx coeff1 = gen_int_mode (factor, mode);
val = expand_mult (mode, val, coeff1, NULL_RTX, false, true);
}
and it's this call to expand_mult that fails. We're asking for a signed
multiplication (unsignedp=false), we're not allowing libcalls
(no_libcall=true), and we have -ftrapv. It appears that the expand code can't
handle this (we would normally use a libcall here on aarch64).
So I guess one option might be to punt to the else case if the expand_mult
fails.
An interesting question is whether we even want a trapping multiplication here?
Is -ftrapv only meant to trap for multiplications that the user wrote or also
those generated by the compiler?
