Re: semantics of null lang_hooks.callgraph.expand_function?

[Jim Wilson <wilson at specifix dot com>]

Dueway Qi wrote:
> I have found another similar case.
> lang_hooks.callgraph.analyze_expr  in  gcc/gcc/cgraphunit.c
>     490           if (lang_hooks.callgraph.analyze_expr)
>     491             return lang_hooks.callgraph.analyze_expr (tp, walk_subtrees,
>     492                                                       data);
> but in another part of this file
>     517       if ((unsigned int) TREE_CODE (t) >= LAST_AND_UNUSED_TREE_CODE)
>     518         return lang_hooks.callgraph.analyze_expr (tp,
> walk_subtrees, data);

The docs say that analyze_expr is used for unrecognized tree codes.  So 
if a front end will generate unrecognized tree codes, then it must 
define the analyze_expr hook.  This explains the second part of this. 
If we see an unrecognized tree code, then there is no real need to check 
if analyze_expr is defined, because it must be defined.  This means 
someone writing a language front end would get an ICE here, but an end 
user would not.  This could be a bit nicer for a language front end 
writer, but this doesn't look like a serious problem.

For the first part of this, we don't know for sure if we have any 
unrecognized tree codes, so we can't assume that the analyze_expr hook 
is defined.  We must check first.

This is an analysis from just looking at the code.  I haven't tried to 
debug it and see what is really going on.
--
Jim Wilson, GNU Tools Support, http://www.specifix.com