Re: [libav-devel] [PATCH] configure: use -O1 with MSVC by default

[Steve Lhomme]

LGTM

On Wed, Dec 14, 2016 at 9:22 AM, Martin Storsjö  wrote:
> On Tue, 13 Dec 2016, Steve Lhomme wrote:
>
>> From: Steve Lhomme 
>>
>> Otherwise some ARM and other unsupported CPU/OS is linked with -O0
>> ---
>> configure | 1 +
>> 1 file changed, 1 insertion(+)
>
>
> I find the commit message quite hard to understand and easily misleading.
> Would this make more sense?
>
> ---8<---
> configure: Use -O1 with MSVC for --disable-optimizations
>
> Without any optimization flags, MSVC does no dead code elimination (DCE) at
> all, even for the most trivial cases. DCE is a prerequisite for building
> libav correctly, otherwise there are undefined references to functions for
> other architectures and disabled components.
>
> -O1 is the minimal optimization flags for MSVC that does include DCE.
> ---8<---
>
> // Martin
>
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Re: [libav-devel] [PATCH] configure: use -O1 with MSVC by default

[Martin Storsjö]

On Tue, 13 Dec 2016, Steve Lhomme wrote:


From: Steve Lhomme 

Otherwise some ARM and other unsupported CPU/OS is linked with -O0
---
configure | 1 +
1 file changed, 1 insertion(+)


I find the commit message quite hard to understand and easily misleading. 
Would this make more sense?


---8<---
configure: Use -O1 with MSVC for --disable-optimizations

Without any optimization flags, MSVC does no dead code elimination (DCE) 
at all, even for the most trivial cases. DCE is a prerequisite for 
building libav correctly, otherwise there are undefined references to 
functions for other architectures and disabled components.


-O1 is the minimal optimization flags for MSVC that does include DCE.
---8<---

// Martin
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Re: [libav-devel] [PATCH] configure: use -O1 with MSVC by default

[Steve Lhomme]

On Tue, Dec 13, 2016 at 5:17 PM, Diego Biurrun  wrote:
> On Tue, Dec 13, 2016 at 04:23:02PM +0100, Steve Lhomme wrote:
>> On Tue, Dec 13, 2016 at 3:33 PM, Hendrik Leppkes  wrote:
>> > On Tue, Dec 13, 2016 at 2:24 PM, Steve Lhomme  wrote:
>> >> From: Steve Lhomme 
>> >>
>> >> Otherwise some ARM and other unsupported CPU/OS is linked with -O0
>> >> --- a/configure
>> >> +++ b/configure
>> >> @@ -3278,6 +3278,7 @@ probe_cc(){
>> >>  _DEPFLAGS='$(CPPFLAGS) $(CFLAGS) -showIncludes -Zs'
>> >>  _cflags_speed="-O2"
>> >>  _cflags_size="-O1"
>> >> +_cflags_noopt="-O1"
>> >
>> > noopt should only be used with --disable-optimizations, why are you
>> > building with that if thats not what you actually want?
>>
>> That's what I used indeed. But it didn't link because it would try to
>> use all kinds of stuff that are compiled but to be dropped by the
>> linker. If you have another suggestion for this not to happen...
>
> You mean DCE (dead code elimination) does not work? We do indeed
> require DCE to build..

That's the thing, yes. It doesn't work with -O0.

> Diego
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Re: [libav-devel] [PATCH] configure: use -O1 with MSVC by default

[Diego Biurrun]

On Tue, Dec 13, 2016 at 04:23:02PM +0100, Steve Lhomme wrote:
> On Tue, Dec 13, 2016 at 3:33 PM, Hendrik Leppkes  wrote:
> > On Tue, Dec 13, 2016 at 2:24 PM, Steve Lhomme  wrote:
> >> From: Steve Lhomme 
> >>
> >> Otherwise some ARM and other unsupported CPU/OS is linked with -O0
> >> --- a/configure
> >> +++ b/configure
> >> @@ -3278,6 +3278,7 @@ probe_cc(){
> >>  _DEPFLAGS='$(CPPFLAGS) $(CFLAGS) -showIncludes -Zs'
> >>  _cflags_speed="-O2"
> >>  _cflags_size="-O1"
> >> +_cflags_noopt="-O1"
> >
> > noopt should only be used with --disable-optimizations, why are you
> > building with that if thats not what you actually want?
> 
> That's what I used indeed. But it didn't link because it would try to
> use all kinds of stuff that are compiled but to be dropped by the
> linker. If you have another suggestion for this not to happen...

You mean DCE (dead code elimination) does not work? We do indeed
require DCE to build..

Diego
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Re: [libav-devel] [PATCH] configure: use -O1 with MSVC by default

[Vittorio Giovara]

On Tue, Dec 13, 2016 at 10:23 AM, Steve Lhomme  wrote:
> On Tue, Dec 13, 2016 at 3:33 PM, Hendrik Leppkes  wrote:
>> On Tue, Dec 13, 2016 at 2:24 PM, Steve Lhomme  wrote:
>>> From: Steve Lhomme 
>>>
>>> Otherwise some ARM and other unsupported CPU/OS is linked with -O0
>>> ---
>>>  configure | 1 +
>>>  1 file changed, 1 insertion(+)
>>>
>>> diff --git a/configure b/configure
>>> index 6d809f7..251b7c4 100755
>>> --- a/configure
>>> +++ b/configure
>>> @@ -3278,6 +3278,7 @@ probe_cc(){
>>>  _DEPFLAGS='$(CPPFLAGS) $(CFLAGS) -showIncludes -Zs'
>>>  _cflags_speed="-O2"
>>>  _cflags_size="-O1"
>>> +_cflags_noopt="-O1"
>>
>> noopt should only be used with --disable-optimizations, why are you
>> building with that if thats not what you actually want?
>
> That's what I used indeed. But it didn't link because it would try to
> use all kinds of stuff that are compiled but to be dropped by the
> linker. If you have another suggestion for this not to happen...
>

Should -O0 be used for noopt?
-- 
Vittorio
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Re: [libav-devel] [PATCH] configure: use -O1 with MSVC by default

[Steve Lhomme]

On Tue, Dec 13, 2016 at 3:33 PM, Hendrik Leppkes  wrote:
> On Tue, Dec 13, 2016 at 2:24 PM, Steve Lhomme  wrote:
>> From: Steve Lhomme 
>>
>> Otherwise some ARM and other unsupported CPU/OS is linked with -O0
>> ---
>>  configure | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/configure b/configure
>> index 6d809f7..251b7c4 100755
>> --- a/configure
>> +++ b/configure
>> @@ -3278,6 +3278,7 @@ probe_cc(){
>>  _DEPFLAGS='$(CPPFLAGS) $(CFLAGS) -showIncludes -Zs'
>>  _cflags_speed="-O2"
>>  _cflags_size="-O1"
>> +_cflags_noopt="-O1"
>
> noopt should only be used with --disable-optimizations, why are you
> building with that if thats not what you actually want?

That's what I used indeed. But it didn't link because it would try to
use all kinds of stuff that are compiled but to be dropped by the
linker. If you have another suggestion for this not to happen...

> - Hendrik
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Re: [libav-devel] [PATCH] configure: use -O1 with MSVC by default

[Hendrik Leppkes]

On Tue, Dec 13, 2016 at 2:24 PM, Steve Lhomme  wrote:
> From: Steve Lhomme 
>
> Otherwise some ARM and other unsupported CPU/OS is linked with -O0
> ---
>  configure | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/configure b/configure
> index 6d809f7..251b7c4 100755
> --- a/configure
> +++ b/configure
> @@ -3278,6 +3278,7 @@ probe_cc(){
>  _DEPFLAGS='$(CPPFLAGS) $(CFLAGS) -showIncludes -Zs'
>  _cflags_speed="-O2"
>  _cflags_size="-O1"
> +_cflags_noopt="-O1"

noopt should only be used with --disable-optimizations, why are you
building with that if thats not what you actually want?

- Hendrik
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[libav-devel] [PATCH] configure: use -O1 with MSVC by default

[Steve Lhomme]

From: Steve Lhomme 

Otherwise some ARM and other unsupported CPU/OS is linked with -O0
---
 configure | 1 +
 1 file changed, 1 insertion(+)

diff --git a/configure b/configure
index 6d809f7..251b7c4 100755
--- a/configure
+++ b/configure
@@ -3278,6 +3278,7 @@ probe_cc(){
 _DEPFLAGS='$(CPPFLAGS) $(CFLAGS) -showIncludes -Zs'
 _cflags_speed="-O2"
 _cflags_size="-O1"
+_cflags_noopt="-O1"
 if $_cc -nologo- 2>&1 | grep -q Linker; then
 _ld_o='-out:$@'
 else
-- 
2.10.2

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