http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52395
--- Comment #10 from Martin Jambor <jamborm at gcc dot gnu.org> 2012-02-27
16:25:15 UTC ---
(In reply to comment #4)
> Martin, can we make sure that 'base' as passed to build_ref_for_offset
> is not artificially constructed by any of its callers? Thus, that it is
> at most the result of stripping some handled-component-refs from an
> existing reference tree (that was not wrapped inside an ADDR_EXPR) in the IL?
As you noticed in PR 52402 IPA-SRA code does not use this function and
IPA-CP only does so when the address argument is a global declaration,
which should be always handled well by expand, I hope.
However, I believe it's the plain ordinary SRA which can introduce,
accesses which the base did not have before. Consider function foo in
the following testcase:
--------------------------------------------------
typedef long long __m128i __attribute__ ((__vector_size__ (16),
__may_alias__));
typedef unsigned int uint32_t;
extern void abort ();
typedef struct
{
__m128i b;
int a;
} s_1a;
typedef s_1a s_1m __attribute__((aligned(1)));
typedef struct
{
char c;
s_1m s;
} __attribute__((packed)) s_2;
void __attribute__((noinline, noclone))
foo (s_1m *p)
{
__m128i v1 = {1,1};
s_1a l;
l = *p;
l.b = v1;
*p = l;
}
int
main (int argc, char **argv)
{
__m128i v2 = {3,4};
long long z[2];
s_2 x;
x.s.b = v2;
foo (&x.s);
__builtin_memcpy (&z, &x.s.b, sizeof (x.s.b));
if (z[0] != 1 || z[1] != 1)
abort ();
return 0;
}
--------------------------------------------------
The original foo:
l = *p_2(D);
l.b = { 1, 1 };
*p_2(D) = l;
is basically converted into (optimized dump):
p_2(D)->b = { 1, 1 };
so we have introduced a non-BLKmode access into a base which did not
have it previously. I am not sure whether this fits your definition
of base which was already there or not. On the other hand, this
testcase passes with the patch from comment 6 (but fails with PR 50444
fix reverted) and SRA never creates anything more beastly than this,
i.e. forwarding scalar loads/stores across aggregate assignments.
Does that answer your question?
