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2014-01-22  Jerome Guitton  <guitton@adacore.com>

	* mlib-tgt-specific-vxworks.adb (Get_Target_Suffix): Replace xscale by
	arm.

2014-01-22  Robert Dewar  <dewar@adacore.com>

	* gnat_rm.texi, gnat_ugn.texi: Document passive task optimization

From-SVN: r206919
This commit is contained in:
Arnaud Charlet 2014-01-22 12:17:01 +01:00
parent 3044bbe427
commit 54533a0b36
4 changed files with 57 additions and 2 deletions
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9
gcc/ada/ChangeLog
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@ -1,3 +1,12 @@
2014-01-22 Jerome Guitton <guitton@adacore.com>
* mlib-tgt-specific-vxworks.adb (Get_Target_Suffix): Replace xscale by
arm.
2014-01-22 Robert Dewar <dewar@adacore.com>
* gnat_rm.texi, gnat_ugn.texi: Document passive task optimization
2014-01-22 Eric Botcazou <ebotcazou@adacore.com>
* gcc-interface/Makefile.in: Minor fixes.

3
gcc/ada/gnat_rm.texi
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@ -5060,6 +5060,9 @@ desired. If the argument @code{No} is present, the task must not be
optimized. GNAT does not attempt to optimize any tasks in this manner
(since protected objects are available in place of passive tasks).
For more information on the subject of passive tasks, see the section
``Passive Task Optimization'' in the GNAT Users Guide.
@node Pragma Persistent_BSS
@unnumberedsec Pragma Persistent_BSS
@findex Persistent_BSS

43
gcc/ada/gnat_ugn.texi
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@ -10154,6 +10154,7 @@ some guidelines on debugging optimized code.
* Other Optimization Switches::
* Optimization and Strict Aliasing::
* Aliased Variables and Optimization::
* Passive Task Optimization::
@ifset vms
* Coverage Analysis::
@ -10999,6 +11000,48 @@ inhibits optimizations that assume the value cannot be assigned.
This means that the above example will in fact "work" reliably,
that is, it will produce the expected results.
@node Passive Task Optimization
@subsection Passive Task Optimization
@cindex Passive Task
A passive task is one which is sufficiently simple that
in theory a compiler could recognize it an implement it
efficiently without creating a new thread. The original design
of Ada 83 had in mind this kind of passive task optimization, but
only a few Ada 83 compilers attempted it. The problem was that
it was difficult to determine the exact conditions under which
the optimization was possible. The result is a very fragile
optimization where a very minor change in the program can
suddenly silently make a task non-optimizable.
With the revisiting of this issue in Ada 95, there was general
agreement that this approach was fundamentally flawed, and the
notion of protected types was introduced. When using protected
types, the restrictions are well defined, and you KNOW that the
operations will be optimized, and furthermore this optimized
performance is fully portable.
Although it would theoretically be possible for GNAT to attempt to
do this optimization, but it really doesn't make sense in the
context of Ada 95, and none of the Ada 95 compilers implement
this optimization as far as we know. In particular GNAT never
attempts to perform this optimization.
In any new Ada 95 code that is written, you should always
use protected types in place of tasks that might be able to
be optimized in this manner.
Of course this does not help if you have legacy Ada 83 code
that depends on this optimization, but it is unusual to encounter
a case where the performance gains from this optimization
are significant.
Your program should work correctly without this optimization. If
you have performance problems, then the most practical
approach is to figure out exactly where these performance problems
arise, and update those particular tasks to be protected types. Note
that typically clients of the tasks who call entries, will not have
to be modified, only the task definition itself.
@ifset vms
@node Coverage Analysis
@subsection Coverage Analysis

4
gcc/ada/mlib-tgt-specific-vxworks.adb
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@ -7,7 +7,7 @@
-- --
-- B o d y --
-- --
-- Copyright (C) 2003-2011, Free Software Foundation, Inc. --
-- Copyright (C) 2003-2013, Free Software Foundation, Inc. --
-- --
-- GNAT is free software; you can redistribute it and/or modify it under --
-- terms of the GNU General Public License as published by the Free Soft- --
@ -157,7 +157,7 @@ package body MLib.Tgt.Specific is
return "sparc";
elsif Target_Name (Target_Name'First .. Index) = "sparc64" then
return "sparc64";
elsif Target_Name (Target_Name'First .. Index) = "xscale" then
elsif Target_Name (Target_Name'First .. Index) = "arm" then
return "arm";
elsif Target_Name (Target_Name'First .. Index) = "i586" then
return "pentium";