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New option to do fine grain control [on|off] of micro-arch specific features : -mtune-ctrl=....


Hi, GCC/i386 currently has about 73 boolean parameters/knobs (defined
in ix86_tune_features[], indexed by ix86_tune_indices) to perform
micro-arch specific performance tuning. However such settings are hard
coded (fixed with a given -mtune setting) and is very hard to do
performance experiment.

The attached patch fixes the problem. The patch introduces a new
option -mtune-ctrl=. Its parameter is a comma separated list of
feature names to turn on associated features. Feature name can be
prefixed by ^ to do the opposite. For instance,

  -mtune-ctrl=prologue_using_move,epilogue_using_move,^pad_returns

tells the compiler to use move instructions in prologue/epilogue
(instead of push/pop), and *not* pad return instructions.

To facilitate the change, the feature tuning enums defined in i386.h
are moved to a new file x86-tune.def and this file can be used to
generate both the enums and names of the features.


Ok for trunk?


thanks,

David

2013-08-03  Xinliang David Li  <davidxl@google.com>

        * config/i386/i386.opt: New option -mtune-ctrl=.
        * config/i386/x86-tune.def: New file.
        * config/i386/i386.h: include x86-tune.def.
        * config/i386/i386.c (ix86_option_override_internal):
        Parsing -mtune-ctrl= option and set tune features.

Attachment: mtune-ctrl.p.txt
Description: Text document


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