Re: [PATCH] tree-optimization/106912 - IPA profile and pure/const

[Jan Hubicka <hubicka@ucw.cz>]

> 
> I have in the meantime briefly tested following.
> 
> But if you want to the above way, then at least the testcase could be
> useful.  Though, not sure if the above is all that is needed.  Shouldn't
> set_const_flag_1 upon TREE_READONLY (node->decl) = 0; also adjust
> TREE_TYPE on the function to
> 	  tree fntype = TREE_TYPE (node->decl);
> 	  TREE_TYPE (node->decl)
> 	    = build_qualified_type (fntype,
> 				    TYPE_QUALS (fntype) & ~TYPE_QUAL_CONST);
> too (perhaps guarded on TREE_READONLY (fntype))?
> 
> 2023-03-16  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR tree-optimization/106912
> gcc/
> 	* calls.h (ignore_const_fntype): Declare.
> 	* calls.cc (flags_from_decl_or_type): Ignore TYPE_READONLY
> 	on types if ignore_const_fntype.
> 	* tree-profile.cc: Include calls.h.
> 	(tree_profiling): Set ignore_const_fntype if profile_arc_flag
> 	or flag_test_coverage.
> gcc/lto/
> 	* lto-lang.cc (lto_post_options): Set ignore_const_fntype if
> 	profile_arc_flag or flag_test_coverage and not flag_auto_profile.
> gcc/testsuite/
> 	* gcc.dg/pr106912.c: New test.
> 
> --- gcc/calls.h.jj	2023-01-02 09:32:51.252868185 +0100
> +++ gcc/calls.h	2023-03-16 12:23:51.632460586 +0100
> @@ -134,5 +134,6 @@ extern void maybe_complain_about_tail_ca
>  
>  extern rtx rtx_for_static_chain (const_tree, bool);
>  extern bool cxx17_empty_base_field_p (const_tree);
> +extern bool ignore_const_fntype;
>  
>  #endif // GCC_CALLS_H
> --- gcc/calls.cc.jj	2023-02-21 11:44:48.460464845 +0100
> +++ gcc/calls.cc	2023-03-16 12:27:45.427032110 +0100
> @@ -800,6 +800,13 @@ is_tm_builtin (const_tree fndecl)
>    return false;
>  }
>  
> +/* Set if flags_from_decl_or_type should ignore TYPE_READONLY of function
> +   types.  This is used when tree-profile.cc instruments const calls,
> +   clears TREE_READONLY on FUNCTION_DECLs which have been instrumented, but
> +   for function types or indirect calls we don't know if the callees have been
> +   instrumented or not.  */
> +bool ignore_const_fntype;
> +
>  /* Detect flags (function attributes) from the function decl or type node.  */
>  
>  int
> @@ -849,7 +856,7 @@ flags_from_decl_or_type (const_tree exp)
>      }
>    else if (TYPE_P (exp))
>      {
> -      if (TYPE_READONLY (exp))
> +      if (TYPE_READONLY (exp) && !ignore_const_fntype)

I think we want to ignore PURE flag too: if callee modifies counters
seen by caller, we need to take that into account when optimizing it.

It is not very pretty to have global flag for prifled state, but I can't
think of scenario where this would break, so perhaps it is good way to
go?

Honza