Re: [PATCH] ipa: Avoid excessive removing of SSAs (PR 113757)

[Martin Jambor <mjambor@suse.cz>]

Hello,

and ping please.

Martin


On Thu, Feb 08 2024, Martin Jambor wrote:
> Hi,
>
> PR 113757 shows that the code which was meant to debug-reset and
> remove SSAs defined by LHSs of calls redirected to
> __builtin_unreachable can trigger also when speculative
> devirtualization creates a call to a noreturn function (and since it
> is noreturn, it does not bother dealing with its return value).
>
> What is more, it seems that the code handling this case is not really
> necessary.  I feel slightly idiotic about this because I have a
> feeling that I added it because of a failing test-case but I can
> neither find the testcase nor a reason why the code in
> cgraph_edge::redirect_call_stmt_to_callee would not be sufficient (it
> turns the SSA name into a default-def, a bit like IPA-SRA, but any
> code dominated by a call to a noreturn is not dangerous when it comes
> to its side-effects).  So this patch just removes the handling.
>
> Bootstrapped and tested on x86_64-linux and ppc64le-linux.  I have also
> LTO-bootstrapped and LTO-profilebootstrapped the patch on x86_64-linux.
>
> OK for master?
>
> Thanks,
>
> Martin
>
>
> gcc/ChangeLog:
>
> 2024-02-07  Martin Jambor  <mjambor@suse.cz>
>
> 	PR ipa/113757
> 	* tree-inline.cc (redirect_all_calls): Remove code adding SSAs to
> 	id->killed_new_ssa_names.
>
> gcc/testsuite/ChangeLog:
>
> 2024-02-07  Martin Jambor  <mjambor@suse.cz>
>
> 	PR ipa/113757
> 	* g++.dg/ipa/pr113757.C: New test.
> ---
>  gcc/testsuite/g++.dg/ipa/pr113757.C | 14 ++++++++++++++
>  gcc/tree-inline.cc                  | 14 ++------------
>  2 files changed, 16 insertions(+), 12 deletions(-)
>  create mode 100644 gcc/testsuite/g++.dg/ipa/pr113757.C
>
> diff --git a/gcc/testsuite/g++.dg/ipa/pr113757.C b/gcc/testsuite/g++.dg/ipa/pr113757.C
> new file mode 100644
> index 00000000000..885d4010a10
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/ipa/pr113757.C
> @@ -0,0 +1,14 @@
> +// { dg-do compile }
> +// { dg-options "-O2 -fPIC" }
> +// { dg-require-effective-target fpic }
> +
> +long size();
> +struct ll {  virtual int hh();  };
> +ll  *slice_owner;
> +int ll::hh() { __builtin_exit(0); }
> +int nn() {
> +  if (size())
> +    return 0;
> +  return slice_owner->hh();
> +}
> +int (*a)() = nn;
> diff --git a/gcc/tree-inline.cc b/gcc/tree-inline.cc
> index 75c10eb7dfc..cac41b4f031 100644
> --- a/gcc/tree-inline.cc
> +++ b/gcc/tree-inline.cc
> @@ -2984,23 +2984,13 @@ redirect_all_calls (copy_body_data * id, basic_block bb)
>        gimple *stmt = gsi_stmt (si);
>        if (is_gimple_call (stmt))
>  	{
> -	  tree old_lhs = gimple_call_lhs (stmt);
>  	  struct cgraph_edge *edge = id->dst_node->get_edge (stmt);
>  	  if (edge)
>  	    {
>  	      if (!id->killed_new_ssa_names)
>  		id->killed_new_ssa_names = new hash_set<tree> (16);
> -	      gimple *new_stmt
> -		= cgraph_edge::redirect_call_stmt_to_callee (edge,
> -		    id->killed_new_ssa_names);
> -	      if (old_lhs
> -		  && TREE_CODE (old_lhs) == SSA_NAME
> -		  && !gimple_call_lhs (new_stmt))
> -		/* In case of IPA-SRA removing the LHS, the name should have
> -		   been already added to the hash.  But in case of redirecting
> -		   to builtin_unreachable it was not and the name still should
> -		   be pruned from debug statements.  */
> -		id->killed_new_ssa_names->add (old_lhs);
> +	      cgraph_edge::redirect_call_stmt_to_callee (edge,
> +		id->killed_new_ssa_names);
>  
>  	      if (stmt == last && id->call_stmt && maybe_clean_eh_stmt (stmt))
>  		gimple_purge_dead_eh_edges (bb);
> -- 
> 2.43.0