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Re: [PATCH] Fix code hoisting dataflow computation order


> The computation of VBEIN and VBEOUT in gcse.c's code hoisting
> implementation appears to be performed in the wrong order, if you ask me.
>
> The explanation is in my list of issues with gcc's code hoisting
> implementation, see
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33828#c9

This seems quite obvious now. :-)  Thanks for spotting it.

> With the attached patch, compute_code_hoist_vbeinout() does converge
> in two iterations for the test case in that Bugzilla comment.
>
> This patch has not been properly tested yet. I'm posting it mostly
> because this is such an embarrassing mistake, and because this might
> be acceptable for gcc 4.3 as a bug fix (there should be a noticeable
> compiler speed improvement when compiling large functions with -Os).

Yes, I think it's reasonable for 4.3.

> If someone wants to pick this up and give it the necessary TLC to get
> it into the FSF gcc,, please go ahead :-)

I'm going to try an -Os bootstrap w/ and w/o the change.

-- 
Eric Botcazou


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