CTools:ICI:Projects:GSOC09:Fine grain tuning

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Revision as of 12:51, 11 August 2009

Google Summer of Code 2009: fine-grain optimizations.

Yuanjie Huang (ICT, China)

This project aims to provide fine-grain optimization selection and tuning abilities in GCC, and thus enable GCC to tune default optimization heuristic of the compiler or fine optimizations for a given program on a given architecture entirely automatically using statistical and machine learning techniques from the MILEPOST project.

• GSOC'09 project description
• SVN repository
• cTuning development mailing list

ICI Fine-grain tuning work flow

Coming soon...

Compilation recording information to XML

Compilation reusing information from XML

ICI Events

ICI events added to the framework for fine-grain tuning are documented here.

ICI Features

New Features

ICI features added to the framework for fine-grain tuning are documented here.

Known Issue of ICI 2.0 Features

• "function_filename" can be empty for functions generated by IPCP optimization (cp pass).

ICI Parameters

ICI Parameter with Type

ICI parameters now come with a type which should be declared when registering parameters in ICI, currently only a few basic C types are supported: void, char, unsigned char, int, unsigned int, long and unsigned long. A special type named EP_SILENT is introduced to pass parameters that is only used to pass status information to plugin; it's actually int, and is planned to be replaced by a elegant solution. The parameter type is defined in gcc/highlev-plugin-internal.h and gcc/highlev-plugin.h:

/* Datatype of event parameter pointer  */
typedef enum
{
  EP_SILENT,
  EP_VOID,
  EP_CHAR,
  EP_UNSIGNED_CHAR,
  EP_INT;
  EP_UNSIGNED_INT,
  EP_LONG,
  EP_UNSIGNED_LONG
} event_parameter_type;

The representation of parameters is defined in file gcc/events.c:

/* Parameter structure.  */
struct event_parameter
{
  const char *name;            /* Name for the parameter */
  const void *value;           /* Pointer to data */
  event_parameter_type type;   /* Type enumeration of value */
};

TODOs of ICI parameter

• Implement ICI control information with ICI features, and remove EP_SILENT type.

ICI API

Parameter Management

register_event_parameter: register a new ICI parameter

get_event_parameter_type: get the type of an ICI event parameter

Pass Management

run_pass: run a pass

run_ipa_pass: run an IPA pass

initialize_ici_pass_list: initialize a list of passes for ICI batch execution

insert_ici_pass_list: insert a pass into ICI pass list

run_ici_pass_list: execute an ICI pass list on current function

run_ici_pass_list_per_function: execute an ICI pass list on current call graph

delete_ici_pass_list: delete an ICI pass list

Adapt Plugin

Description

Adapt plugin provides support for GCC pass sequence record/substitution, function-specific optimization tuning, function clone and instrumentation. Plugins developed for fine-grain tuning are documented here. These plugins are developed to work with ICI-2.0 interface.

HOWTO

Adapt plugin is depends on Mini-XML library, which provides XML reading and writing ability.

This plugin behaves differently depending on the ICI_ADAPT_CONTROL environmental variable, which can be either set to 1 to record information of current compilation into XML files or to 2 to reuse passes from XML files to perform passes substitution, function clone and other functionalities.

To use adapt plugin with ICI, ICI_PLUGIN environment variable should be set to the path to the plugin library (.so), and gcc should be called with with either -fici flag or ICI_USE environment parameter.

Pass recoding/substitution

Adapt plugin can be used to record or substite pass during compilation with information from XML files.

XML file structure

Here's XML file structure used in Adapt plugin, defined in DTD syntax (Draft):

<!ELEMENT ici (plugin, compiler, function)>

<!ELEMENT plugin (plugin_name, plugin_version)>
<!ELEMENT plugin_name (#PCDATA)>
<!ELEMENT plugin_version (#PCDATA)>

<!ELEMENT compiler (compiler_version)>
<!ELEMENT compiler_version (#PCDATA)>

<!ELEMENT function (optimizaton_options, (ipa_pass_list|gimple_pass_list)?)>
<!ATTLIST function function_name #REQUIRED>
<!ATTLIST function function_filename #REQUIRED>
<!ATTLIST function function_start_line #IMPLIED>
<!ATTLIST function function_end_line #IMPLIED>

<!ELEMENT optimizaton_options (#PCDATA)>

<!ELEMENT ipa_pass_list (pass*)>
<!ELEMENT gimple_pass_list (pass*)>

<!ELEMENT pass (parameter*, loop*)>
<!ATTLIST pass pass_name #REQUIRED>

<!ELEMENT loop (parameter*)>
<!ATTLIST loop loop_id #REQUIRED>

<!ELEMENT parameter (#PCDATA)>

Fine-grain parameter tuning

XML format

Parameters and other information for fine grain tuning is saved in the same XML files as parameter tuning, the structure of XML file is disribed with DTD in pass recording/substitution sector.

Known issues

• During loop-unroll optimization, wrong optimization heuristics might be applied to loops as a result of different loop id (loop->num) across compilations.

Function specific optimization options

Adapt plugin makes it possible to set function specific optimizations with XML files. The optimizations options is given in the same format as command line arguments, and represented in a plain character string tagged <optimization_options> in <function> tag.

Known issues

Function specific optimization options tuning is still experimental and cannot handle the following situation:

• If the command line optimization for the whole program is based on -O0 or -O1, but a function is specified to be compiled with -O2 or -O3, compilation will fail.