https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89765
--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> ---
Btw, the C notation
typedef unsigned __int128 V __attribute__((vector_size (sizeof (__int128))));
V
foo (unsigned __int128 x, V y, int z)
{
y[0] = x;
}
on x86_64 prouces
{
VIEW_CONVERT_EXPR<__int128 unsigned[1]>(y)[0] = x;
}
the array-ref prevents the gimplification into SSA. That also works
for variable indices btw. It is eventually turns into
BIT_FIELD_REF <y, 128, 0> = x_2(D);
by gimplification first and then
y_5 = BIT_INSERT_EXPR <y_4(D), x_2(D), 0 (128 bits)>;
by update-address-taken. Not sure why the folding doesn't trigger here
but does for ppc64. The BIT_FIELD_REF is produced by
maybe_canonicalize_mem_ref_addr which uses build3 instead of fold_build3
to build the BIT_FIELD_REF (probably not expecting simplification or
avoding constant folding on the LHS). Indeed using fold_build3 there
gets us
VIEW_CONVERT_EXPR<__int128 unsigned>(y) = x;
