Phase ordering in compiler

Phase ordering in compiler

[vikram1729]

Dear Sir,
	I want to understand the phase-ordering problem in compilers. My basic
doubt is what is the  difference between the pass and phase in compilers? As
for as I know, Pass something that scans to through the input code snippet
and does some transformation to it and whereas phases in the classicle
compiler are main components/modules which are Lexical Analysis, Parsing,
semantic analysis, IL code Generation, Code Optimization and code
Generation. 

When it comes to phase-ordering in compilers is it actually pass ordering or
phase-ordering? 
How the user can handle/alter phase-ordering in GCC? 
Is it only through changing the order of the optimization options fed to the
compiler or 
by tweaking the pass_manager? 
Will there be any impact of repeating optimization options or reordering the
optimization options in GCC?
Thanks in Advance,

VSP



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Re: Phase ordering in compiler

[Ian Lance Taylor]

On Sun, Oct 21, 2012 at 11:47 PM, vikram1729 <vsp1729@gmail.com> wrote:
> Dear Sir,
>         I want to understand the phase-ordering problem in compilers. My basic
> doubt is what is the  difference between the pass and phase in compilers?

There is no significant difference.  One might think of a phase a
group of passes.  Still, it would be reasonable to describe the
phase-ordering problem as a pass-ordering problem.

> How the user can handle/alter phase-ordering in GCC?

You can edit the source code (gcc/passes.c) or you could write a
plugin but there is no way to change the ordering from the command
line.

> Will there be any impact of repeating optimization options or reordering the
> optimization options in GCC?

Yes.

Ian

Re: Phase ordering in compiler

[SANKAR]

When there is an impact of repeating optimisation options or reordering the
optimisation options in GCC, is this pass ordering enabled through command
line? 

Sankar



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Re: Phase ordering in compiler

[Andrew Haley]

On 10/23/2012 06:21 AM, SANKAR wrote:
> When there is an impact of repeating optimisation options or reordering the
> optimisation options in GCC, is this pass ordering enabled through command
> line? 

Not usually, because passes often rely on changes made before them.
Sometimes a pass will work if reordered or duplicated, sometimes not.

Andrew.