This is the mail archive of the
mailing list for the GCC project.
Re: [PATCH] Fix PR middle-end/17746
- From: Eric Botcazou <ebotcazou at libertysurf dot fr>
- To: gcc-patches at gcc dot gnu dot org
- Cc: kenner at vlsi1 dot ultra dot nyu dot edu (Richard Kenner)
- Date: Wed, 20 Oct 2004 09:56:21 +0200
- Subject: Re: [PATCH] Fix PR middle-end/17746
- References: <10410192219.AA14305@vlsi1.ultra.nyu.edu>
> Then the above is not valid! handled_component_p and get_inner_reference
> must always agree on what's handled. The bug is in handled_component_p.
Very interesting. You added the supplementary check for VIEW_CONVERT_EXPR
without updating handled_component_p. For the FSF tree:
For GNAT 5.x:
2002-10-16 Richard Kenner <firstname.lastname@example.org>
* expr.c (get_inner_reference): Don't go through a VIEW_CONVERT_EXPR
whose purpose is to step up the alignment.
I can't imagine this is an oversight. If it is, all the GNAT 5.x compilers
are affected by the "bug".
Here's my take on this. My initial reaction when investigating the problem
was similar to yours: why on Earth is there this obvious gap between
get_inner_reference and handled_component_p? I found your patch and
immediately added the missing bits to handled_component_p. Then things
started to break because is_gimple_addressable now returns false for this
kind of VIEW_CONVERT_EXPR.
I came to the conclusion that returning true for them in handled_component_p
is a good solution (and that you probably came to it too). They are handled
like the other VIEW_CONVERT_EXPRs except that, when they are expanded, an
additional step is performed:
op0 = expand_expr (TREE_OPERAND (exp, 0), NULL_RTX, mode, modifier);
/* At this point, OP0 is in the correct mode. If the output type is such
that the operand is known to be aligned, indicate that it is.
Otherwise, we need only be concerned about alignment for non-BLKmode
if (MEM_P (op0))
op0 = copy_rtx (op0);
if (TYPE_ALIGN_OK (type))
set_mem_align (op0, MAX (MEM_ALIGN (op0), TYPE_ALIGN (type)));
that is, the super-alignment is recorded.
This has worked fine up to 3.4.x because ADDR_EXPR was handled by recursive
calls to expand_expr. For 4.0, ADDR_EXPR is handled by the specialized
expand_expr_addr_expr, which doesn't invoke expand_expr anymore. My patch
simply lets expand_expr_addr_expr be aware of these VIEW_CONVERT_EXPRs.
> The proposed fix is to teach expand_expr_addr_expr_1 to look itself
> through the VIEW_CONVERT_EXPR nodes that "step up" the alignment, but
> only if they carry the TYPE_ALIGN_OK flag.
> In that case get_inner_reference should *also* look at TYPE_ALIGN_OK,
> as should handled_component_p.
get_inner_reference already looks at TYPE_ALIGN_OK and actually rejects
VIEW_CONVERT_EXPR because of it.