| Message ID | 56E78500.1040309@redhat.com |
|---|---|
| State | New |
| Headers | show |
On Tue, Mar 15, 2016 at 4:44 AM, Richard Henderson <rth@redhat.com> wrote: > The problem here is that > > void* labels[] = { > &&l0, &&l1, &&l2 > }; > > gets gimplified to > > labels = *.LC0; > > but .LC0 is not in the set of local decls, so that when copy_forbidden is > called during sra versioning we fail to forbid the copy. We could set a > different flag, but I think it's easiest to just add the artificial decl to > where it can be seen. > > Ok? Hmm. tree_output_constant_def uses the global constant pool (and not function-scope statics). So while for the above case with local labels there can be no sharing and thus the decl is really "local" with non-local labels or with other random initializers you'd have the ctor decl in multiple local decl vectors. Not sure if that's a problem, but at least if you'd have void* labels[] = { &&l0, &&l1, &&l2 }; void* labels2[] = { &&l0, &&l1, &&l2 }; you'll end up with the same constant pool decl in local-decls twice. Given cross-function sharing is generally possible doing the addition to local-decls only if we create a new constant pool entry isn't enough either. It's also a bit pre-mature in the gimplifier as we only add to local-decls during BIND expr lowering. I also wonder if outputting the constant pool decl far away from the labels might end up with invalid asm for some targets. Well, I don't see any convenient way of fixing things here either but maybe we can do if (walk_tree_without_duplicataes (&DECL_INITIAL (ctor), has_label_address_in_static_1, cfun->decl)) add_local_decl (cfun, ctor); to avoid adding the decl when it is not necessary. Having another struct function flag would be possible as well, or re-use has_nonlocal_label as clearly a global static is now refering to a local label (you'd lose optimization when 'labels' becomes unused of course). Thanks, Richard. > > r~
diff --git a/gcc/gimplify.c b/gcc/gimplify.c index b331e41..884482e 100644 --- a/gcc/gimplify.c +++ b/gcc/gimplify.c @@ -4016,6 +4016,7 @@ gimplify_init_constructor (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p, walk_tree (&ctor, force_labels_r, NULL, NULL); ctor = tree_output_constant_def (ctor); + add_local_decl (cfun, ctor); if (!useless_type_conversion_p (type, TREE_TYPE (ctor))) ctor = build1 (VIEW_CONVERT_EXPR, type, ctor); TREE_OPERAND (*expr_p, 1) = ctor;
The problem here is that void* labels[] = { &&l0, &&l1, &&l2 }; gets gimplified to labels = *.LC0; but .LC0 is not in the set of local decls, so that when copy_forbidden is called during sra versioning we fail to forbid the copy. We could set a different flag, but I think it's easiest to just add the artificial decl to where it can be seen. Ok? r~ * gimplify.c (gimplify_init_constructor): Add the constant def decl to the function's local decls.