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Re: [PATCH] gcc 8: Implement -felide-function-bodies


On 2017.04.01 at 01:00 -0400, David Malcolm wrote:
> The following patch implements a new function-body-elision
> optimization, which can dramatically improve performance,
> especially under certain benchmarks.
> 
> gcc/ChangeLog:
> 	* common.opt (felide-function-bodies): New option.
> 	* gimplify.c (gimplify_body): Implement function-body
> 	elision.
> 
> diff --git a/gcc/common.opt b/gcc/common.opt
> index 4021622..a32a56d 100644
> --- a/gcc/common.opt
> +++ b/gcc/common.opt
> @@ -1299,6 +1299,10 @@ fipa-sra
>  Common Report Var(flag_ipa_sra) Init(0) Optimization
>  Perform interprocedural reduction of aggregates.
>  
> +felide-function-bodies
> +Common Optimization Var(flag_elide_function_bodies)
> +Perform function body elision optimization
> +
>  feliminate-unused-debug-symbols
>  Common Report Var(flag_debug_only_used_symbols)
>  Perform unused symbol elimination in debug info.
> diff --git a/gcc/gimplify.c b/gcc/gimplify.c
> index fbf136f..4853953 100644
> --- a/gcc/gimplify.c
> +++ b/gcc/gimplify.c
> @@ -12390,6 +12390,9 @@ gimplify_body (tree fndecl, bool do_parms)
>       the body so that DECL_VALUE_EXPR gets processed correctly.  */
>    parm_stmts = do_parms ? gimplify_parameters () : NULL;
>  
> +  if (flag_elide_function_bodies)
> +    DECL_SAVED_TREE (fndecl) = NULL_TREE;
> +
>    /* Gimplify the function's body.  */
>    seq = NULL;
>    gimplify_stmt (&DECL_SAVED_TREE (fndecl), &seq);

Haha, your option also has dramatic binary size saving effects.
I would suggest to enable it unconditionally on every April Fools' Day.

-- 
Markus


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