[PATCH] ipa-visibility: remove assert in TLS optimization [PR107353]

[PATCH] ipa-visibility: remove assert in TLS optimization [PR107353]

[Alexander Monakov]

When upgrading TLS access model based on optimized symbol visibility
status, we attempted to assert that recomputing the model would not
weaken it. It turns out that C, C++, and Fortran front-ends all can
(unintentionally) assign a stronger model than what can be derived
from the declaration.

Let's act conservatively instead of asserting, at least as long as
such pre-existing issues remain.

gcc/ChangeLog:

	PR other/107353
	* ipa-visibility.cc (function_and_variable_visibility):
	Conditionally upgrade TLS model instead of asserting.
---
 gcc/ipa-visibility.cc | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/gcc/ipa-visibility.cc b/gcc/ipa-visibility.cc
index 3ed2b7cf6..238f7eb84 100644
--- a/gcc/ipa-visibility.cc
+++ b/gcc/ipa-visibility.cc
@@ -886,8 +886,12 @@ function_and_variable_visibility (bool whole_program)
 	      && vnode->ref_list.referring.length ())
 	    {
 	      enum tls_model new_model = decl_default_tls_model (decl);
-	      gcc_checking_assert (new_model >= decl_tls_model (decl));
-	      set_decl_tls_model (decl, new_model);
+	      STATIC_ASSERT (TLS_MODEL_GLOBAL_DYNAMIC < TLS_MODEL_LOCAL_DYNAMIC);
+	      STATIC_ASSERT (TLS_MODEL_INITIAL_EXEC < TLS_MODEL_LOCAL_EXEC);
+	      /* We'd prefer to assert that recomputed model is not weaker than
+		 what the front-end assigned, but cannot: see PR 107353.  */
+	      if (new_model >= decl_tls_model (decl))
+		set_decl_tls_model (decl, new_model);
 	    }
 	}
     }
-- 
2.37.2

Re: [PATCH] ipa-visibility: remove assert in TLS optimization [PR107353]

[Martin Jambor]

Hi,

On Wed, Oct 26 2022, Alexander Monakov wrote:
> When upgrading TLS access model based on optimized symbol visibility
> status, we attempted to assert that recomputing the model would not
> weaken it. It turns out that C, C++, and Fortran front-ends all can
> (unintentionally) assign a stronger model than what can be derived
> from the declaration.

If you believe that FEs assign a wrong model sometimes (that is my
impression after reading your bugzilla comments), please open bugs for
those cases.

>
> Let's act conservatively instead of asserting, at least as long as
> such pre-existing issues remain.
>
> gcc/ChangeLog:
>
> 	PR other/107353
> 	* ipa-visibility.cc (function_and_variable_visibility):
> 	Conditionally upgrade TLS model instead of asserting.

The patch is OK (assuming it passes bootstrap&testing).

Thanks,

Martin


> ---
>  gcc/ipa-visibility.cc | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/gcc/ipa-visibility.cc b/gcc/ipa-visibility.cc
> index 3ed2b7cf6..238f7eb84 100644
> --- a/gcc/ipa-visibility.cc
> +++ b/gcc/ipa-visibility.cc
> @@ -886,8 +886,12 @@ function_and_variable_visibility (bool whole_program)
>  	      && vnode->ref_list.referring.length ())
>  	    {
>  	      enum tls_model new_model = decl_default_tls_model (decl);
> -	      gcc_checking_assert (new_model >= decl_tls_model (decl));
> -	      set_decl_tls_model (decl, new_model);
> +	      STATIC_ASSERT (TLS_MODEL_GLOBAL_DYNAMIC < TLS_MODEL_LOCAL_DYNAMIC);
> +	      STATIC_ASSERT (TLS_MODEL_INITIAL_EXEC < TLS_MODEL_LOCAL_EXEC);
> +	      /* We'd prefer to assert that recomputed model is not weaker than
> +		 what the front-end assigned, but cannot: see PR 107353.  */
> +	      if (new_model >= decl_tls_model (decl))
> +		set_decl_tls_model (decl, new_model);
>  	    }
>  	}
>      }
> -- 
> 2.37.2