OpenE2K/gcc
2
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

invoke.texi (Optimization Options): Clean up -O flag descriptions.

Browse Source 
* gcc/doc/invoke.texi (Optimization Options): Clean up -O flag
	descriptions.

From-SVN: r60696
This commit is contained in:
Jerry Quinn 2002-12-31 14:59:09 +00:00 committed by Gerald Pfeifer
parent fad893da14
commit 147d1cd3bb
2 changed files with 30 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
gcc/ChangeLog
View File

@ -1,3 +1,8 @@
2002-12-31 Jerry Quinn <jlquinn@optonline.net>
* gcc/doc/invoke.texi (Optimization Options): Clean up -O flag
descriptions.
2002-12-31 Jerry Quinn <jlquinn@optonline.net>
* gcc/doc/invoke.texi (Optimization Options): List the options

52
gcc/doc/invoke.texi
View File

@ -3369,7 +3369,22 @@ is used when GCC itself is being built.) @xref{Spec Files}.
@cindex optimize options
@cindex options, optimization
These options control various sorts of optimizations:
These options control various sorts of optimizations.
Without any optimization option, the compiler's goal is to reduce the
cost of compilation and to make debugging produce the expected
results. Statements are independent: if you stop the program with a
breakpoint between statements, you can then assign a new value to any
variable or change the program counter to any other statement in the
function and get exactly the results you would expect from the source
code.
Turning on optimization flags makes the compiler attempt to improve
the performance and/or code size at the expense of compilation time
and possibly the ability to debug the program.
Not all optimizations are controlled directly by a flag. Only
optimizations that have a flag are listed.
@table @gcctabopt
@item -O
@ -3379,13 +3394,6 @@ These options control various sorts of optimizations:
Optimize. Optimizing compilation takes somewhat more time, and a lot
more memory for a large function.
Without @option{-O}, the compiler's goal is to reduce the cost of
compilation and to make debugging produce the expected results.
Statements are independent: if you stop the program with a breakpoint
between statements, you can then assign a new value to any variable or
change the program counter to any other statement in the function and
get exactly the results you would expect from the source code.
With @option{-O}, the compiler tries to reduce code size and execution
time, without performing any optimizations that take a great deal of
compilation time.
@ -3462,10 +3470,15 @@ the last such option is the one that is effective.
Options of the form @option{-f@var{flag}} specify machine-independent
flags. Most flags have both positive and negative forms; the negative
form of @option{-ffoo} would be @option{-fno-foo}. In the table below,
only one of the forms is listed---the one which is not the default.
You can figure out the other form by either removing @samp{no-} or
adding it.
form of @option{-ffoo} would be @option{-fno-foo}. In the table
below, only one of the forms is listed---the one you typically will
use. You can figure out the other form by either removing @samp{no-}
or adding it.
The following options control specific optimizations. They are either
activated by @option{-O} options or are related to ones that are. You
can use the following flags in the rare cases when ``fine-tuning'' of
optimizations to be performed is desired.
@table @gcctabopt
@item -ffloat-store
@ -3731,21 +3744,6 @@ indices used to access arrays are within the declared range. This is
currently only supported by the Java and Fortran 77 front-ends, where
this option defaults to true and false respectively.
@end table
The following options control specific optimizations. The @option{-O2}
option turns on all of these optimizations except @option{-funroll-loops}
and @option{-funroll-all-loops}. On most machines, the @option{-O} option
turns on the @option{-fthread-jumps} and @option{-fdelayed-branch} options,
but specific machines may handle it differently.
You can use the following flags in the rare cases when ``fine-tuning''
of optimizations to be performed is desired.
Not all of the optimizations performed by GCC have @option{-f} options
to control them.
@table @gcctabopt
@item -fstrength-reduce
@opindex fstrength-reduce
Perform the optimizations of loop strength reduction and