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From: Dehao Chen <dehao@google.com>
To: Xinliang David Li <davidxl@google.com>
Cc: Ian Lance Taylor <iant@google.com>,
	Eric Botcazou <ebotcazou@adacore.com>,
		GCC Patches <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH] Reset source location for instructions moved out of its original residing basic block
Date: Thu, 01 Nov 2012 23:16:00 -0000	[thread overview]
Message-ID: <CAO2gOZU-ZT2UdsRPjBKh0_hTGczj7B9rupJ58s7X30vBKLaomA@mail.gmail.com> (raw)
In-Reply-To: <CAAkRFZLw2Y4dAGiDkYiL8w5_WtLt__O0=--Zzj2A19dA80iOuA@mail.gmail.com>

On Thu, Nov 1, 2012 at 4:07 PM, Xinliang David Li <davidxl@google.com> wrote:
> On Thu, Nov 1, 2012 at 3:57 PM, Ian Lance Taylor <iant@google.com> wrote:
>> On Thu, Nov 1, 2012 at 10:00 AM, Dehao Chen <dehao@google.com> wrote:
>>>
>>> I see your point. How about we guard these changes with a flag, say
>>> -gless-jumpy, so that people can always choose between better coverage
>>> and less jumpy gdb behavior (it's also important for some other
>>> clients like AutoFDO). I will have a series of patches to follow soon
>>> that can be guarded by this flag.
>>
>> This feels to me like an attempt to address the problem in the wrong
>> place.  It seems to me that it would be better to do one of:
>>
>> * Use -Og and ensure that -Og does not move the code around.
>> Presumably this would lead to worse runtime performance and better
>> performance in the debugger.
>>
>> * Add heuristics to the debugger to jump around less.
>>
>> * Add a new debug facility to mark the statement as attached to a
>> particular source location, but moved relative to other source
>> locations.  Add facilities to the debugger to take that into account.
>>
>> That said, I suppose I can imagine a mode like you suggest.  It
>> shouldn't be a -g option, it should be a -f option, like
>> -fdiscard-moved-insn-debug-locations or something.  That would be
>> along the lines of -fno-var-tracking: we generate worse debug info
>> upon user request.

I don't see why debug info would be worse if we add something like
-fdiscard-moved-insn-debug-locations, as long as it is not turned on
by default. Any thoughts?

>>
>
> Or have a common umbrella option to guard all changes that improves DOC.

Is it like -Og approach as Ian mentioned? Yes, we can sacrifice some
performance (maybe 5%?) to get more accurate source level profile. But
if we plan to use AutoFDOed binary to collect AutoFDO profile, it'll
suffer the same debug problem again...

Thanks,
Dehao

>
> David
>
>
>
>> Ian

  reply	other threads:[~2012-11-01 23:16 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-11-01  5:03 Dehao Chen
2012-11-01  8:56 ` Eric Botcazou
2012-11-01 14:36   ` Dehao Chen
2012-11-01 15:04     ` Eric Botcazou
2012-11-01 17:00       ` Dehao Chen
2012-11-01 22:57         ` Ian Lance Taylor
2012-11-01 23:07           ` Xinliang David Li
2012-11-01 23:16             ` Dehao Chen [this message]
2012-11-01 23:36               ` Xinliang David Li
2012-11-04 22:26         ` Alexandre Oliva
2012-11-26 14:47           ` Richard Biener

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