list of optimizations done by -O1 level

list of optimizations done by -O1 level

[ranjith kumar]

Hi,
 GCC manuals says the foloowing are the list of
optimizations turned on when -O1 flag is used.
-------------------------------------------------------
 -fdefer-pop -fdelayed-branch       
-fguess-branch-probability -fcprop-registers
-floop-optimize -fif-conversion
           -fif-conversion2 -ftree-ccp -ftree-dce
-ftree-dominator-opts -ftree-dse
           -ftree-ter -ftree-lrs -ftree-sra
-ftree-copyrename -ftree-fre -ftree-ch
           -fmerge-constants
           -O also turns on -fomit-frame-pointer on
machines where doing so does not
           interfere with debugging.

           -O doesnÂ’t turn on -ftree-sra for the Ada
compiler.  This option must be
           explicitly specified on the command line to
be enabled for the Ada compiler.
----------------------------------------------------

But When I compiled the same file as in the following
2 ways, I got two differen assembly programs. What
could be the reason. 
Thanks in advance.


1) gcc -march=pentium4 -O1 -S res22.c
2) gcc -march=pentium4 -fdefer-pop -fdelayed-branch   
    -fguess-branch-probability -fcprop-registers
-floop-optimize -fif-conversion
           -fif-conversion2 -ftree-ccp -ftree-dce
-ftree-dominator-opts -ftree-dse
           -ftree-ter -ftree-lrs -ftree-sra
-ftree-copyrename -ftree-fre -ftree-ch
           -fmerge-constants -fomit-frame-pointer
-ftree-sra 
  -S res22.c
Are there any extra optimizations turned on while
using -O1 options???????????????
Below is the res22.c program.
-------------------------------------------------------
-------------------------------------------------------
 1 #include <stdio.h>
      2 #include <xmmintrin.h>
      3  unsigned  int x , y,p,val,x1;
      4
      5 __m128 a, b, c;
      6
      7 float inp_sse1[4] __attribute__((aligned(16)))
= { 1.2, 3.5, 1.7, 2.8 };
      8 float inp_sse2[4]
__attribute__((aligned(16)))= { -0.7, 2.6, 3.3, -4.0
};
      9 float out_sse[4] __attribute__((aligned(16)));
     10 void f()
     11 {
     12
     13    c = _mm_add_ps(a, b);
     14    _mm_store_ps(out_sse,c);
     15 }
     16
     17
     18 int main(void){
     19  int i,j;
     20
     21 a = _mm_load_ps(inp_sse1);
     22    b = _mm_load_ps(inp_sse2);
     23
     24 //for(j=0;j<999;j++)
     25 //  for(i = 0; i < 9999; i++)
     26 f();
     27
     28 for(i = 0; i < 4; i++) {
     29     printf("Result %d: %.2f\n",i,out_sse[i]);
     30 }



		
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Re: list of optimizations done by -O1 level

[Ian Lance Taylor]

ranjith kumar <ranjit_kumar_b4u@yahoo.co.uk> writes:

>  GCC manuals says the foloowing are the list of
> optimizations turned on when -O1 flag is used.
> -------------------------------------------------------
>  -fdefer-pop -fdelayed-branch       
> -fguess-branch-probability -fcprop-registers
> -floop-optimize -fif-conversion
>            -fif-conversion2 -ftree-ccp -ftree-dce
> -ftree-dominator-opts -ftree-dse
>            -ftree-ter -ftree-lrs -ftree-sra
> -ftree-copyrename -ftree-fre -ftree-ch
>            -fmerge-constants
>            -O also turns on -fomit-frame-pointer on
> machines where doing so does not
>            interfere with debugging.
> 
>            -O doesn’t turn on -ftree-sra for the Ada
> compiler.  This option must be
>            explicitly specified on the command line to
> be enabled for the Ada compiler.
> ----------------------------------------------------

The gcc manual also says:

    Not all optimizations are controlled directly by a flag.  Only
    optimizations that have a flag are listed.

Ian

Re: list of optimizations done by -O1 level

[Daniel Lohmann]

ranjith kumar schrieb:
> Hi,
>  GCC manuals says the foloowing are the list of
> optimizations turned on when -O1 flag is used.
> ...
> 
> But When I compiled the same file as in the following
> 2 ways, I got two differen assembly programs. What
> could be the reason. 

Besides the explicit set of optimizations, there is also a general 
optimize-flag used within gcc. This flag is set by the -O option itself.

Daniel

Re: list of optimizations done by -O1 level

[John Love-Jensen]

Hi Ranjith,

I don't have an answer to your inquiry, but here's a helpful trick to answer
the "Hmmm, I wonder what flags are controlled by the optimization level
flags?" ...

echo '' | g++     -fverbose-asm -S -x c++ - -o blank.s
echo '' | g++ -O0 -fverbose-asm -S -x c++ - -o O0.s
echo '' | g++ -O1 -fverbose-asm -S -x c++ - -o O1.s
echo '' | g++ -O2 -fverbose-asm -S -x c++ - -o O2.s
echo '' | g++ -O3 -fverbose-asm -S -x c++ - -o O3.s
echo '' | g++ -Os -fverbose-asm -S -x c++ - -o Os.s

Note: there are optimizations above-and-beyond the ones that are
identifiable by a specific named flag.

HTH,
--Eljay

Re: list of optimizations done by -O1 level

[ranjith kumar]

--- Ian Lance Taylor <iant@google.com> wrote:

> ranjith kumar <ranjit_kumar_b4u@yahoo.co.uk> writes:
> 
> >  GCC manuals says the foloowing are the list of
> > optimizations turned on when -O1 flag is used.
> >
>
-------------------------------------------------------
> >  -fdefer-pop -fdelayed-branch       
> > -fguess-branch-probability -fcprop-registers
> > -floop-optimize -fif-conversion
> >            -fif-conversion2 -ftree-ccp -ftree-dce
> > -ftree-dominator-opts -ftree-dse
> >            -ftree-ter -ftree-lrs -ftree-sra
> > -ftree-copyrename -ftree-fre -ftree-ch
> >            -fmerge-constants
> >            -O also turns on -fomit-frame-pointer
> on
> > machines where doing so does not
> >            interfere with debugging.
> > 
> >            -O doesnÂ’t turn on -ftree-sra for the
> Ada
> > compiler.  This option must be
> >            explicitly specified on the command
> line to
> > be enabled for the Ada compiler.
> >
> ----------------------------------------------------
> 
> The gcc manual also says:
> 
>     Not all optimizations are controlled directly by
> a flag.  Only
>     optimizations that have a flag are listed.
> 
> Ian
> 
Sorry. What do you mean?


Is there any way to find list of optimizations enabled
by -O1?

Actually when I explicitly specified  all
optimizations, there were function calls associated
with each SIMD function called in .c file.
But when I used -O1 flag they were not present in
assembly code.
I am intrested in knowing which optimization is
replacing those function calls and at what
intermediate representation that optimization is done?

Thanks.



	
	
		
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Re: list of optimizations done by -O1 level

[Andrew Haley]

ranjith kumar writes:
 > 
 > 
 > Is there any way to find list of optimizations enabled
 > by -O1?

-fverbose-asm.  The list is in the top of the .s file.

 > Actually when I explicitly specified  all
 > optimizations, there were function calls associated
 > with each SIMD function called in .c file.
 > But when I used -O1 flag they were not present in
 > assembly code.
 > I am intrested in knowing which optimization is
 > replacing those function calls and at what
 > intermediate representation that optimization is done?

Use -fdump-tree-all and have a look.

Andrew.

Re: list of optimizations done by -O1 level

[ranjith kumar]

--- Andrew Haley <aph@redhat.com> wrote:

> ranjith kumar writes:
>  > 
>  > 
>  > Is there any way to find list of optimizations
> enabled
>  > by -O1?
> 
> -fverbose-asm.  The list is in the top of the .s
> file.
No. That option shows some list of optimizations.
But when I compiled with all those list of
optimizations instead of -O1, the effetct was not
same.
Any help please.
> 
>  > Actually when I explicitly specified  all
>  > optimizations, there were function calls
> associated
>  > with each SIMD function called in .c file.
>  > But when I used -O1 flag they were not present in
>  > assembly code.
>  > I am intrested in knowing which optimization is
>  > replacing those function calls and at what
>  > intermediate representation that optimization is
> done?
> 
> Use -fdump-tree-all and have a look.
> 
> Andrew.
> 



		
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Re: list of optimizations done by -O1 level

[Andrew Haley]

ranjith kumar writes:
 > 
 > --- Andrew Haley <aph@redhat.com> wrote:
 > 
 > > ranjith kumar writes:
 > >  > 
 > >  > 
 > >  > Is there any way to find list of optimizations
 > > enabled
 > >  > by -O1?
 > > 
 > > -fverbose-asm.  The list is in the top of the .s
 > > file.
 > No. That option shows some list of optimizations.

It is the list of optimization passes that were run.

 > But when I compiled with all those list of
 > optimizations instead of -O1, the effetct was not
 > same.

Quite a lot of optimizations are controlled by "if (optimize)",
regardless of what list of passes was supplied.  

There is no list of optimizations that you can supply to gcc that will
replicate the effect of -O1.

Andrew.

Re: list of optimizations done by -O1 level

[Christopher Layne]

On Thu, Feb 22, 2007 at 05:24:07PM +0000, ranjith kumar wrote:
> Is there any way to find list of optimizations enabled
> by -O1?
> 
> Actually when I explicitly specified  all
> optimizations, there were function calls associated
> with each SIMD function called in .c file.
> But when I used -O1 flag they were not present in
> assembly code.

And you did not use -msse -msse2 or -mtune=x at the same time as specifying
the other flags?

-cl