Re: [PATCH PR/82546] tree node size

[Richard Biener <rguenther@suse.de>]

On October 13, 2017 8:29:40 PM GMT+02:00, Nathan Sidwell <nathan@acm.org> wrote:
>[Although I filed this as a middle-end bug, it's really a core infra 
>bug, not sure who the best reviewer is]
>
>In working on tree streaming in the modules branch, I discovered poor 
>tree node size and hierarchy bits.
>
>Here's a fix for the first part of that.  tree.c (tree_code_size) 
>returns sizeof (tree_type_non_common) for any tcc_type node. That's 
>wasteful, given we have tree_type_common-> 
>tree_type_with_lang_specific-> tree_type_non_common available as 
>choices.  It's also obscuring defects in (at least) the c++ FE where we
>
>use tree_type_non_common fields, but claim the node doesn't contain
>that 
>structure.   Ew.
>
>This patch makes tree_code_size ask the lang hook for the size of 
>non-core type nodes.  It also fixes the c++ and objc FEs to return a 
>size for the nodes it cares about.
>
>I don't (yet) know whether all the core types are tree_type_non_common,
>
>nor whether the FE's can return smaller sizes than the do with this 
>patch.  But at least the control flow is now correct.  during
>developing 
>this patch I added an assert that the lang hook was returning a size at
>
>least as big as tree_type_non_common, so they couldn't be more broken 
>than before the patch.
>
>I intend to continue cleaning this up of course.  It's not clear to me 
>whether we should cache these node sizes in an array, and the way it 
>goes about checking nodes with nested switches is understandable, but 
>possible not the fastest solution. However let's at least get the
>sizing 
>right first.

We were conservative exactly to avoid the langhook here. I think there's similar 'bug' on the decl side. 

Richard. 

>ok?
>
>nathan