PR61629 (was Re: Delay RTL initialization until it is really needed)

[Richard Sandiford]

Richard Sandiford <rdsandiford@googlemail.com> writes:
> Jan Hubicka <hubicka@ucw.cz> writes:
>> Hi,
>
>> IRA initialization shows high in profiles even when building lto
>> objects.  This patch simply delays RTL backend initialization until we
>> really decide to output a function.  In some cases this avoids the
>> initialization completely (like in the case of LTO but also user
>> target attributes) and there is some hope for better cache locality.
>>
>> Basic idea is to have two flags saying whether lang and target
>> dependent bits needs initialization and check it when starting
>> function codegen.
>>
>> Bootstrapped/regtested x86_64-linux, testing also at AIX. Ok if it passes?
>>
>> Honza
>>
>> 	* toplev.c (backend_init_target): Move init_emit_regs and init_regs to...
>> 	(backend_init) ... here; skip ira_init_once and backend_init_target.
>> 	(target_reinit) ... and here; clear this_target_rtl->lang_dependent_initialized.
>> 	(lang_dependent_init_target): Clear this_target_rtl->lang_dependent_initialized;
>> 	break out rtl initialization to ...
>> 	(initialize_rtl): ... here; call also backend_init_target and ira_init_once.
>> 	* toplev.h (initialize_rtl): New function.
>> 	* function.c: Include toplev.h
>> 	(init_function_start): Call initialize_rtl.
>> 	* rtl.h (target_rtl): Add target_specific_initialized,
>> 	lang_dependent_initialized.
>> Index: toplev.c
>> ===================================================================
>> --- toplev.c	(revision 211837)
>> +++ toplev.c	(working copy)
>> @@ -1583,14 +1583,6 @@ backend_init_target (void)
>>    /* Initialize alignment variables.  */
>>    init_alignments ();
>>  
>> -  /* This reinitializes hard_frame_pointer, and calls init_reg_modes_target()
>> -     to initialize reg_raw_mode[].  */
>> -  init_emit_regs ();
>> -
>> -  /* This invokes target hooks to set fixed_reg[] etc, which is
>> -     mode-dependent.  */
>> -  init_regs ();
>> -
>>    /* This depends on stack_pointer_rtx.  */
>>    init_fake_stack_mems ();
>>  
>> @@ -1632,9 +1624,13 @@ backend_init (void)
>>    init_varasm_once ();
>>    save_register_info ();
>>  
>> -  /* Initialize the target-specific back end pieces.  */
>> -  ira_init_once ();
>> -  backend_init_target ();
>> +  /* Middle end needs this initialization for default mem attributes
>> +     used by early calls to make_decl_rtl.  */
>> +  init_emit_regs ();
>> +
>> +  /* Middle end needs this initialization for mode tables used to assign
>> +     modes to vector variables.  */
>> +  init_regs ();
>
> This causes a segfault on gcc.target/mips/umips-store16-1.c.  The register
> asm:
>
> register unsigned int global asm ("$16");
>
> causes us to globalise $16 and call reinit_regs.  reinit_regs in turn
> calls ira_init, but IRA hasn't been initialised at this point and
> prerequisites like init_fake_stack_mems haven't yet been called.
>
> Does the patch below look OK?
>
>> @@ -1686,6 +1682,31 @@ lang_dependent_init_target (void)
>>       front end is initialized.  It also depends on the HAVE_xxx macros
>>       generated from the target machine description.  */
>>    init_optabs ();
>> +  this_target_rtl->lang_dependent_initialized = false;
>> +}
>> +
>> +/* Perform initializations that are lang-dependent or target-dependent.
>> +   but matters only for late optimizations and RTL generation.  */
>> +
>> +void
>> +initialize_rtl (void)
>> +{
>> +  static int initialized_once;
>> +
>> +  /* Initialization done just once per compilation, but delayed
>> +     till code generation.  */
>> +  if (!initialized_once)
>> +    ira_init_once ();
>> +  initialized_once = true;
>> +
>> +  /* Target specific RTL backend initialization.  */
>> +  if (!this_target_rtl->target_specific_initialized)
>> +    backend_init_target ();
>> +  this_target_rtl->target_specific_initialized = true;
>> +
>> +  if (this_target_rtl->lang_dependent_initialized)
>> +    return;
>> +  this_target_rtl->lang_dependent_initialized = true;
>>  
>>    /* The following initialization functions need to generate rtl, so
>>       provide a dummy function context for them.  */
>
> Why do you need both these flags?  We only call this function once
> the language has been initialised, so we should always be initialising
> both sets of information (backend_init_target and the stuff after
> the comment above, from the old lang_dependent_init_target).
>
> How about the second patch below, still under testing?  The new assert
> is OK for target_reinit because it has:
>
>   this_target_rtl->target_specific_initialized = false;
>
>   /* This initializes hard_frame_pointer, and calls init_reg_modes_target()
>      to initialize reg_raw_mode[].  */
>   init_emit_regs ();
>
>   /* This invokes target hooks to set fixed_reg[] etc, which is
>      mode-dependent.  */
>   init_regs ();
>
>   /* Reinitialize lang-dependent parts.  */
>   lang_dependent_init_target ();
>
> i.e. it sets the flag to say that the RTL stuff hasn't been initialised
> and then goes on to initialise everything that needs to be deferred.

Now tested on mips64-linux-gnu.  OK for both patches?

> Thanks,
> Richard
>
>
> gcc/
> 	PR rtl-optimization/61629
> 	* reginfo.c (reinit_regs): Only call ira_init and recog_init if
> 	they have already been initialized.
>
> Index: gcc/reginfo.c
> ===================================================================
> --- gcc/reginfo.c	2014-07-16 07:59:00.039669668 +0100
> +++ gcc/reginfo.c	2014-07-16 07:59:00.397672987 +0100
> @@ -533,8 +533,11 @@ reinit_regs (void)
>    init_regs ();
>    /* caller_save needs to be re-initialized.  */
>    caller_save_initialized_p = false;
> -  ira_init ();
> -  recog_init ();
> +  if (this_target_rtl->target_specific_initialized)
> +    {
> +      ira_init ();
> +      recog_init ();
> +    }
>  }
>  
>  /* Initialize some fake stack-frame MEM references for use in
>
>
> gcc/
> 	* rtl.h (target_rtl): Remove lang_dependent_initialized.
> 	* toplev.c (initialize_rtl): Don't use it.  Move previously
> 	"language-dependent" calls to...
> 	(backend_init): ...here.
> 	(lang_dependent_init_target): Don't set lang_dependent_initialized.
> 	Assert that RTL initialization hasn't happend yet.
>
> Index: gcc/rtl.h
> ===================================================================
> --- gcc/rtl.h	2014-07-11 11:55:14.265158363 +0100
> +++ gcc/rtl.h	2014-07-16 08:16:23.245370141 +0100
> @@ -2517,7 +2517,6 @@ struct GTY(()) target_rtl {
>  
>    /* Track if RTL has been initialized.  */
>    bool target_specific_initialized;
> -  bool lang_dependent_initialized;
>  };
>  
>  extern GTY(()) struct target_rtl default_target_rtl;
> Index: gcc/toplev.c
> ===================================================================
> --- gcc/toplev.c	2014-07-11 11:54:41.604838961 +0100
> +++ gcc/toplev.c	2014-07-16 08:22:36.226034738 +0100
> @@ -1604,6 +1604,10 @@ backend_init_target (void)
>       on a mode change.  */
>    init_expmed ();
>    init_lower_subreg ();
> +  init_set_costs ();
> +
> +  init_expr_target ();
> +  ira_init ();
>  
>    /* We may need to recompute regno_save_code[] and regno_restore_code[]
>       after a mode change as well.  */
> @@ -1682,7 +1686,8 @@ lang_dependent_init_target (void)
>       front end is initialized.  It also depends on the HAVE_xxx macros
>       generated from the target machine description.  */
>    init_optabs ();
> -  this_target_rtl->lang_dependent_initialized = false;
> +
> +  gcc_assert (!this_target_rtl->target_specific_initialized);
>  }
>  
>  /* Perform initializations that are lang-dependent or target-dependent.
> @@ -1701,26 +1706,10 @@ initialize_rtl (void)
>  
>    /* Target specific RTL backend initialization.  */
>    if (!this_target_rtl->target_specific_initialized)
> -    backend_init_target ();
> -  this_target_rtl->target_specific_initialized = true;
> -
> -  if (this_target_rtl->lang_dependent_initialized)
> -    return;
> -  this_target_rtl->lang_dependent_initialized = true;
> -
> -  /* The following initialization functions need to generate rtl, so
> -     provide a dummy function context for them.  */
> -  init_dummy_function_start ();
> -
> -  /* Do the target-specific parts of expr initialization.  */
> -  init_expr_target ();
> -
> -  /* Although the actions of these functions are language-independent,
> -     they use optabs, so we cannot call them from backend_init.  */
> -  init_set_costs ();
> -  ira_init ();
> -
> -  expand_dummy_function_end ();
> +    {
> +      backend_init_target ();
> +      this_target_rtl->target_specific_initialized = true;
> +    }
>  }
>  
>  /* Language-dependent initialization.  Returns nonzero on success.  */