[RFA] Fix Ada bootstrap (was: 16: EH redirection)

[Richard Guenther]

On Sun, Apr 26, 2009 at 1:18 AM, Michael Matz <matz@suse.de> wrote:
> Hi,
>
> in the course of retesting the SSA-expand patches I noticed that Ada
> doesn't bootstrap with an SSA verification error.  I think that's a
> fallout of the EH edge improvements, but haven't verified if backing them
> out would work-around it, as it's anyway a bug in SRA.
>
> SRA in some cases (when the RHS is a bitfield ref) wants to use the
> gimplifier to decompose its complicated expressions into gimple
> statements.  It uses an into-ssa context for that, which mean every LHS
> will automatically get a new SSA name (if is_gimple_reg).
>
> The generated sequence of gimple instructions then is possibly inserted
> into all outgoing edges of the current BB (that happens if there's memory
> accesses and trapping involved).  To copy the sequence (to insert them on
> possibly multiple edges) it uses gimple_copy_seq.  This one only
> deep-copies the instructions, including the SSA names.
>
> Now, if those instructions then finally are inserted onto the edges we
> suddenly have multiple instructions defining the same SSA name --> boom.
>
> The LHS sides of this are marked for renaming, but quite obviously the
> update_ssa code isn't prepared to deal with pre-existing SSA-name defining
> instructions which also are marked for renaming (at least if no old_ or
> new_ssa_names are involved).
>
> So, instead of fiddling with update_ssa for this unusable case, I simply
> changed SRA to not use the into_ssa mode of the gimplifier, but instead to
> rely on usual update_ssa.  This requires also marking all generated
> temporaries (from the gimplifier) for renaming, and not just to mark them
> referenced.  Only SRA uses the gimplifier in that mode explicitely (apart
> from those uses abstracted away in force_gimple_operand and
> gimple_regimplify_operands).
>
> Without this patch r146781 doesn't even build with Ada on x86_64-linux.
> With the patch it builds.
>
> I'm currently regstrapping on x86_64-linux.  Okay if it works?

Ok.

Thanks,
Richard.

>
> Ciao,
> Michael.
> --
>        * tree-sra.c (sra_build_assignment): Don't use into_ssa mode,
>        mark new temporaries for renaming.
>
> Index: tree-sra.c
> ===================================================================
> --- tree-sra.c  (Revision 146781)
> +++ tree-sra.c  (Arbeitskopie)
> @@ -2206,14 +2206,16 @@ sra_build_assignment (tree dst, tree src
>        var = fold_build1 (VIEW_CONVERT_EXPR, TREE_TYPE (dst), var);
>
>       push_gimplify_context (&gctx);
> -      gctx.into_ssa = true;
>       gctx.allow_rhs_cond_expr = true;
>
>       gimplify_assign (dst, var, &seq);
>
>       if (gimple_referenced_vars (cfun))
>        for (var = gctx.temps; var; var = TREE_CHAIN (var))
> -         add_referenced_var (var);
> +         {
> +           add_referenced_var (var);
> +           mark_sym_for_renaming (var);
> +         }
>       pop_gimplify_context (NULL);
>
>       return seq;
>