https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102844
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rguenth at gcc dot gnu.org
Status|ASSIGNED |NEW
Priority|P3 |P2
Assignee|rguenth at gcc dot gnu.org |unassigned at gcc dot
gnu.org
--- Comment #19 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #15)
> The following removes the premature optimization(?) using
> EDGE_NO_COPY_SRC_BLOCK
> in case the block contained a condition we could thread through. That fixes
> the testcase.
>
> diff --git a/gcc/tree-ssa-threadedge.c b/gcc/tree-ssa-threadedge.c
> index c3ea2d680d8..2005e30322b 100644
> --- a/gcc/tree-ssa-threadedge.c
> +++ b/gcc/tree-ssa-threadedge.c
> @@ -989,8 +989,11 @@ thread_around_empty_blocks (edge taken_edge,
> return false;
> bitmap_set_bit (visited, taken_edge->dest->index);
>
> + /* We may not use EDGE_NO_COPY_SRC_BLOCK since the condition
> + might later be simplified to something needing a temporary
> + SSA definition. See PR102844. */
> jump_thread_edge *x
> - = new jump_thread_edge (taken_edge, EDGE_NO_COPY_SRC_BLOCK);
> + = new jump_thread_edge (taken_edge, EDGE_COPY_SRC_BLOCK);
> path->safe_push (x);
>
> thread_around_empty_blocks (taken_edge,
OK, it isn't that easy - we overrun redirection_data::dup_blocks that way
causing random crashes later on. So the change needs adjustments to how
we account thread_around_empty_blocks stuff, I couldn't find the code
that avoids this for non-empty blocks.
The issue is definitely latent everywhere even trunk as long as we keep
the DOM forward threader there.
