-O3 Enabled?

Hei Chan structurechart@yahoo.com
Wed Aug 7 22:28:00 GMT 2013


I was trying to track down why my executable became slower after a certain date.
And I suspected that -O3 was dropped in the new build process at work.
That's why I am trying to find a way to narrow down the issue.


----- Original Message -----
From: Ángel González <keisial@gmail.com>
To: vijay nag <vijunag@gmail.com>
Cc: Hei Chan <structurechart@yahoo.com>; GCC-help <gcc-help@gcc.gnu.org>
Sent: Wednesday, August 7, 2013 9:14 PM
Subject: Re: -O3 Enabled?

On 07/08/13 06:58, vijay nag wrote:
> If you just have the binary without the source, I guess it is
> impossible to figure out optimization level.
>
> If you have source for the same, you can build it with -O0,
> disassemble the code and compare the compiler code emission for a
> particular
> function.
>
> In future, if you would like to know the CFLAGS with which it was
> built, you can export those information to a header as #define's and
> be included
> in one of compilation units.
>
> Vijay Nag
Depending on the compiler/platform/format you could get some hints.
For instance -fomit-frame-pointer would be easy to detect in disassembly.

But it would be a hard and mostly-manual work (and you would probably
need quite a bit of knowledge about gcc phases). I don't think it's worth
trying to figure out.
Do you have a real need for knowing that?



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