On Wed, Nov 22, 2023 at 11:32:10AM +0000, Richard Biener wrote:
> > hack in gcc 13 and triggered on hundreds of tests there within just 5
> > seconds of running make check-g++ -j32 (and in cases I looked at had nothing
> > to do with the r14-5086 backports), so I believe this is just bad
> > assumption on the try_catch_may_fallthru side, gimplify.cc certainly doesn't
> > care, it just calls gimplify_and_add (TREE_OPERAND (*expr_p, 1), &cleanup);
> > on it. So, IMHO non-STATEMENT_LIST in the second operand is equivalent to
> > a STATEMENT_LIST containing a single statement.
>
> Did you check if there's ever a CATCH_EXPR or EH_FILTER_EXPR not wrapped
> inside a STATEMENT_LIST? That is, does
>
> if (TREE_CODE (TREE_OPERAND (stmt, 1)) != STATEMENT_LIST)
> {
> gcc_checking_assert (code != CATCH_EXPR && code != EH_FILTER_EXPR);
> return false;
> }
>
> work?
Looking at a trivial example
void bar ();
void
foo (void)
{
try { bar (); } catch (int) {}
}
it seems it is even more complicated, because what e.g. the gimplification
sees is not TRY_CATCH_EXPR with CATCH_EXPR second operand, but
TRY_BLOCK with HANDLER second operand (note, certainly not wrapped in a
STATEMENT_LIST, one would need another catch (long) {} for it after it),
C++ FE specific trees.
And cp_gimplify_expr then on the fly turns the TRY_BLOCK into TRY_CATCH_EXPR
(in genericize_try_block) and HANDLER into CATCH_EXPR
(genericize_catch_block).
When gimplifying EH_SPEC_BLOCK in genericize_eh_spec_block it even
creates TRY_CATCH_EXPR with genericize_eh_spec_block ->
build_gimple_eh_filter_tree
if even creates TRY_CATCH_EXPR with EH_FILTER_EXPR as its second operand
(without intervening STATEMENT_LIST).
So, I believe the patch is correct but for C++ it might be hard to see it
actually trigger because most often one will see the C++ FE specific trees
of TRY_BLOCK (with HANDLER) and EH_SPEC_BLOCK instead.
So, I wonder why cxx_block_may_fallthru doesn't handle TRY_BLOCK and
EH_SPEC_BLOCK as well. Given the genericization, I think
TRY_BLOCK should be handled similarly to TRY_CATCH_EXPR in tree.cc,
if second operand is HANDLER or STATEMENT_LIST starting with HANDLER,
check if any of the handler bodies can fall thru, dunno if TRY_BLOCK without
HANDLERs is possible, and for EH_SPEC_BLOCK see if the failure can fall
through.
Jakub
