Re: [patch] Perform anonymous constant propagation during inlining

[Richard Biener <richard dot guenther at gmail dot com>]

On May 4, 2015 11:38:42 PM GMT+02:00, Eric Botcazou <ebotcazou@adacore.com> wrote:
>> 2015-05-01  Eric Botcazou  <ebotcazou@adacore.com>
>> 
>> 	* expr.c (expand_expr_real_1) <SSA_NAME>: Try to substitute
>constants
>> 	on the RHS of expressions.
>> 	* gimple-expr.h (is_gimple_constant): Reorder.
>
>Bummer.  This breaks C++ debugging:
>
>+FAIL: gdb.cp/class2.exp: print alpha at marker return 0
>+FAIL: gdb.cp/class2.exp: print beta at marker return 0
>+FAIL: gdb.cp/class2.exp: print * aap at marker return 0
>+FAIL: gdb.cp/class2.exp: print * bbp at marker return 0
>+FAIL: gdb.cp/class2.exp: print * abp at marker return 0, s-p-o off
>+FAIL: gdb.cp/class2.exp: print * (B *) abp at marker return 0
>+FAIL: gdb.cp/class2.exp: p acp
>+FAIL: gdb.cp/class2.exp: p acp->c1
>+FAIL: gdb.cp/class2.exp: p acp->c2
>
>because C++ is apparently relying on the assignment to the anonymous
>return 
>object to preserve the debug info attached to a return statement.
>
>Would you be OK with a slight variation of your earlier idea, i.e.
>calling 
>fold_stmt with a specific valueizer from fold_marked_statements instead
>of the 
>implicit no_follow_ssa_edges in the inliner?  Something like:
>
>tree
>follow_anonymous_single_use_edges (tree val)
>{
>  if (TREE_CODE (val) == SSA_NAME
>      && (!SSA_NAME_VAR (val) || DECL_IGNORED_P (SSA_NAME_VAR (var)))
>      && has_single_use (val))
>    return val
>  return NULL_TREE;
>}

Yes, that works for me as well.

Richard.