insn_elision

insn_elision

[Bharati Bhole]

Hi,
Can anybody plz tell me what is insn_elision in .md files?
It is mentioned in gensupport.c.
Thanks.

Bharati.

Re: insn_elision

[Ian Lance Taylor]

"Bharati Bhole" <bharati.bhole@gmail.com> writes:

> Can anybody plz tell me what is insn_elision in .md files?
> It is mentioned in gensupport.c.

Here is the comment from gensupport.c which explains it.

  /* Discard insn patterns which we know can never match (because
     their C test is provably always false).  If insn_elision is
     false, our caller needs to see all the patterns.  Note that the
     elided patterns are never counted by the sequence numbering; it
     it is the caller's responsibility, when insn_elision is false, not
     to use elided pattern numbers for anything.  */

It may help to know that "elision" is an English word.  It means,
approximately, "omission," which means the act of removing something.
The related word is "elide," which is approximately the same as
"omit."

Ian

Regarding SIMD features of GCC

[ranjith kumar]

Hi,
    I have the following queries:

1) Apart from general optimizations (enabled by -O3
flag), what is the total list of optimizations done by
gcc(GNU C compiler) for Pentium-4 processor?
ie)processor specific optimizations only

Can any one tell any source where I can find them?

2)Where can I find list of functions and data types
defined to exploit SIMD features of Pentium-4
processor  by GCC. (I am familiar with SIMD features
of Pentium-4.)

3) Pentium-4 has special instructions like MOVNTQ,
MOVNTPS ...to enable data from XMM and MMX registers
to be stored to memory using a non-temporal hint.

How to do the same in a  C language?

Can any one help me?
Thanks. 


		
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Re: Regarding SIMD features of GCC

[Tim Prince]

ranjith kumar wrote:
> Hi,
>     I have the following queries:
> 
> 1) Apart from general optimizations (enabled by -O3
> flag), what is the total list of optimizations done by
> gcc(GNU C compiler) for Pentium-4 processor?
> ie)processor specific optimizations only
> 
> Can any one tell any source where I can find them?
An answer which comes to mind is to look in gcc/config/i386, in the 
source distribution.
> 
> 2)Where can I find list of functions and data types
> defined to exploit SIMD features of Pentium-4
> processor  by GCC. (I am familiar with SIMD features
> of Pentium-4.)
How about the architecture specific include files, like <xmmintrin.h>?
 From the title, I thought you might be interested in gcc-4.2 vectorization.
> 
> 3) Pentium-4 has special instructions like MOVNTQ,
> MOVNTPS ...to enable data from XMM and MMX registers
> to be stored to memory using a non-temporal hint.
> 
> How to do the same in a  C language?
Not unless a compiler has a feature for substituting those instructions, 
or you take advantage of <xmmintrin.h>.

RE: Regarding SIMD features of GCC

[John (Eljay) Love-Jensen]

Hi Ranjith,

Sorry - partial answer, may be somewhat tangential.

You can get the compiler to produce a list of optimization produced by a given optimization level list this:

Example for C and -O2:
echo "" | gcc -O2 -fverbose-asm -c -S -x c -; cat ./-.s; rm ./-.s

Example for C++ and -O3:
echo "" | g++ -O3 -fverbose-asm -c -S -x c++ -; cat ./-.s; rm ./-.s

If you have them on your system, one way to access the SSE facilities is through the #include <mmintrin.h> and #include <xmmintrin.h> headers.

HTH,
--Eljay