https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103581
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Btw, it's this loop being vectorized:
int i;
for (i = 0; i < n_basic_blocks; i++)
{
basic_block b = BASIC_BLOCK (i);
TBB d = di.dom[di.dfs_order[b->index]];
/* The old code didn't modify array elements of nodes having only
itself as dominator (d==0) or only ENTRY_BLOCK (resp. EXIT_BLOCK)
(d==1). */
if (d > 1)
idom[i] = di.dfs_to_bb[d]->index;
}
di.dom[] and di.dfs_order[] are unsigned int, b->index is int, the blocks
are fetched from an array of pointers. But the relevant difference is in
the vectorization of the masked (d > 1) gathers where di.dfs_to_bb is
basic_block *[].
struct basic_block { int index; };
void foo (int * __restrict idom, int n_basic_blocks,
unsigned int *indices, struct basic_block **dfs_to_bb)
{
for (int i = 0; i < n_basic_blocks; ++i)
{
unsigned int d = indices[i];
if (d > 1)
idom[i] = dfs_to_bb[d]->index;
}
}
does not vectorize because of alias issues, the .MASK_{LOAD,STORE} generated
by if-conversion do not carry along restrict info ...
Even making the store unconditional does not fix this particular issue.
Even simplified as
struct basic_block { int index; };
void foo (struct basic_block *__restrict *idom, int n_basic_blocks,
unsigned int *indices, struct basic_block * __restrict *dfs_to_bb)
{
for (int i = 0; i < n_basic_blocks; ++i)
{
unsigned int d = indices[i];
struct basic_block *tem;
if (d > 1)
tem = dfs_to_bb[d];
else
tem = 0;
idom[i] = tem;
}
}
does not work :/
