llvm dev - Jan 2014 - [LLVMdev] [cfe-dev] AArch64 Clang CLI interface proposal

I knew I'd regret leaving that option in for the MIPS port back in 99.
Basically this is the only acceptable way for mcpu to exist, but should
never have been added to the GCC aarch64 port at all since there's no
compatibility with existing build systems to worry about.

I would still like you to show this mythical piece of software that needs
this compatibility.

-eric
On Jan 8, 2014 3:06 AM, "Bernie Ogden" <bogden at arm.com>
wrote:
> I think there's an error in the example here.
> http://gcc.gnu.org/onlinedocs/gcc-4.8.2/gcc/AArch64-Options.html still
> documents -mcpu, and that march does not take CPUs as arguments. A local
> GCC developer tells me that the documentation is wrong in that -mcpu is
> actually a shorthand for specifying both -mtune and -march, but that the
> option is certainly there.
>
>
>
> If we want GCC comptability then that's what we have to do, unless
someone
> knows that GCC ARM/AArch64 is actually going to move away from this.
>
>
>
> Do we want GCC compatibility?
>
>
>
> Regards,
>
>
>
> Bernie
>
>
>
>
>
> *From:* cfe-dev-bounces at cs.uiuc.edu [mailto:cfe-dev-bounces at
cs.uiuc.edu] *On
> Behalf Of *Eric Christopher
> *Sent:* 07 January 2014 21:37
> *To:* Renato Golin; Amara Emerson; Clang Dev; LLVM Dev
> *Subject:* Re: [cfe-dev] [LLVMdev] AArch64 Clang CLI interface proposal
>
>
>
> Parsing the arch string is a bit icky, but I don't really have too much
of
> a problem with it - and it's better than -mcpu so...
>
>
>
> -eric
>
>
>
> On Tue Jan 07 2014 at 9:23:43 AM, Renato Golin <renato.golin at
linaro.org>
> wrote:
>
> On 7 January 2014 17:05, Amara Emerson <amara.emerson at arm.com>
wrote:
>
> We plan on implementing this interface for AArch64 Clang in future, and
> completely dropping the current support for -mfpu. This means that -march
> will become the preferred way to specify the target CPU/architecture.
>
>
>
> Hi Amara,
>
>
>
> This is something we were converging on the ARM32 world, too, and I
> believe other targets would probably do the same, if not before us.
> Hopefully, that'd also help clean up the driver's code in the
process.
>
>
>
> cheers,
>
> --renato
>
>
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I'm just stating that _if_ GCC compatibility is desired then we have to have
-mcpu.

I don't think there's software that *needs* the compatibility, but it is
easier for GCC projects to switch to clang if that compatibility is there -
which I think is why we go for GCC compatibility in the first place?

(I raised http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59718 on the GCC docs.)
From: Eric Christopher [mailto:echristo at gmail.com]
Sent: 08 January 2014 12:23
To: Bernard Ogden
Cc: Renato Golin; LLVM Developers Mailing List; Clang Dev; Amara Emerson
Subject: RE: [cfe-dev] [LLVMdev] AArch64 Clang CLI interface proposal


I knew I'd regret leaving that option in for the MIPS port back in 99.
Basically this is the only acceptable way for mcpu to exist, but should never
have been added to the GCC aarch64 port at all since there's no
compatibility with existing build systems to worry about.

I would still like you to show this mythical piece of software that needs this
compatibility.

-eric
On Jan 8, 2014 3:06 AM, "Bernie Ogden" <bogden at
arm.com<mailto:bogden at arm.com>> wrote:
I think there's an error in the example here.
http://gcc.gnu.org/onlinedocs/gcc-4.8.2/gcc/AArch64-Options.html still documents
-mcpu, and that march does not take CPUs as arguments. A local GCC developer
tells me that the documentation is wrong in that -mcpu is actually a shorthand
for specifying both -mtune and -march, but that the option is certainly there.

If we want GCC comptability then that's what we have to do, unless someone
knows that GCC ARM/AArch64 is actually going to move away from this.

Do we want GCC compatibility?

Regards,

Bernie


From: cfe-dev-bounces at cs.uiuc.edu<mailto:cfe-dev-bounces at
cs.uiuc.edu> [mailto:cfe-dev-bounces at cs.uiuc.edu<mailto:cfe-dev-bounces
at cs.uiuc.edu>] On Behalf Of Eric Christopher
Sent: 07 January 2014 21:37
To: Renato Golin; Amara Emerson; Clang Dev; LLVM Dev
Subject: Re: [cfe-dev] [LLVMdev] AArch64 Clang CLI interface proposal

Parsing the arch string is a bit icky, but I don't really have too much of a
problem with it - and it's better than -mcpu so...

-eric

On Tue Jan 07 2014 at 9:23:43 AM, Renato Golin <renato.golin at
linaro.org<mailto:renato.golin at linaro.org>> wrote:
On 7 January 2014 17:05, Amara Emerson <amara.emerson at
arm.com<mailto:amara.emerson at arm.com>> wrote:
We plan on implementing this interface for AArch64 Clang in future, and
completely dropping the current support for -mfpu. This means that -march
will become the preferred way to specify the target CPU/architecture.

Hi Amara,

This is something we were converging on the ARM32 world, too, and I believe
other targets would probably do the same, if not before us. Hopefully,
that'd also help clean up the driver's code in the process.

cheers,
--renato

-- IMPORTANT NOTICE: The contents of this email and any attachments are
confidential and may also be privileged. If you are not the intended recipient,
please notify the sender immediately and do not disclose the contents to any
other person, use it for any purpose, or store or copy the information in any
medium. Thank you.

ARM Limited, Registered office 110 Fulbourn Road, Cambridge CB1 9NJ, Registered
in England & Wales, Company No: 2557590
ARM Holdings plc, Registered office 110 Fulbourn Road, Cambridge CB1 9NJ,
Registered in England & Wales, Company No: 2548782
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I'm just stating that _if_ GCC compatibility is desired then we have to have
-mcpu.

 

I don't think there's software that *needs* the compatibility, but it is
easier for GCC projects to switch to clang if that compatibility is there -
which I think is why we go for GCC compatibility in the first place?

 

(I raised http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59718 on the GCC
docs.)

 

 

From: Eric Christopher [mailto:echristo at gmail.com] 
Sent: 08 January 2014 12:23
To: Bernard Ogden
Cc: Renato Golin; LLVM Developers Mailing List; Clang Dev; Amara Emerson
Subject: RE: [cfe-dev] [LLVMdev] AArch64 Clang CLI interface proposal

 

I knew I'd regret leaving that option in for the MIPS port back in 99.
Basically this is the only acceptable way for mcpu to exist, but should
never have been added to the GCC aarch64 port at all since there's no
compatibility with existing build systems to worry about. 

I would still like you to show this mythical piece of software that needs
this compatibility. 

-eric

On Jan 8, 2014 3:06 AM, "Bernie Ogden" <bogden at arm.com>
wrote:

I think there's an error in the example here.
http://gcc.gnu.org/onlinedocs/gcc-4.8.2/gcc/AArch64-Options.html still
documents -mcpu, and that march does not take CPUs as arguments. A local GCC
developer tells me that the documentation is wrong in that -mcpu is actually
a shorthand for specifying both -mtune and -march, but that the option is
certainly there.

 

If we want GCC comptability then that's what we have to do, unless someone
knows that GCC ARM/AArch64 is actually going to move away from this.

 

Do we want GCC compatibility?

 

Regards,

 

Bernie

 

 

From: cfe-dev-bounces at cs.uiuc.edu [mailto:cfe-dev-bounces at cs.uiuc.edu] On
Behalf Of Eric Christopher
Sent: 07 January 2014 21:37
To: Renato Golin; Amara Emerson; Clang Dev; LLVM Dev
Subject: Re: [cfe-dev] [LLVMdev] AArch64 Clang CLI interface proposal

 

Parsing the arch string is a bit icky, but I don't really have too much of a
problem with it - and it's better than -mcpu so...

 

-eric

 

On Tue Jan 07 2014 at 9:23:43 AM, Renato Golin <renato.golin at
linaro.org>
wrote:

On 7 January 2014 17:05, Amara Emerson <amara.emerson at arm.com> wrote:

We plan on implementing this interface for AArch64 Clang in future, and
completely dropping the current support for -mfpu. This means that -march
will become the preferred way to specify the target CPU/architecture.

 

Hi Amara,

 

This is something we were converging on the ARM32 world, too, and I believe
other targets would probably do the same, if not before us. Hopefully,
that'd also help clean up the driver's code in the process.

 

cheers,

--renato
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We typically add options in clang only if there is a user for them.
On Jan 8, 2014 4:32 AM, "Bernard Ogden" <Bernard.Ogden at
arm.com> wrote:
>  I'm just stating that _if_ GCC compatibility is desired then we have
to
> have -mcpu.
>
>
>
> I don't think there's software that *needs* the compatibility, but
it is
> easier for GCC projects to switch to clang if that compatibility is there -
> which I think is why we go for GCC compatibility in the first place?
>
>
>
> (I raised http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59718 on the GCC
> docs.)
>
>   *From:* Eric Christopher [mailto:echristo at gmail.com]
> *Sent:* 08 January 2014 12:23
> *To:* Bernard Ogden
> *Cc:* Renato Golin; LLVM Developers Mailing List; Clang Dev; Amara Emerson
> *Subject:* RE: [cfe-dev] [LLVMdev] AArch64 Clang CLI interface proposal
>
>
>
> I knew I'd regret leaving that option in for the MIPS port back in 99.
> Basically this is the only acceptable way for mcpu to exist, but should
> never have been added to the GCC aarch64 port at all since there's no
> compatibility with existing build systems to worry about.
>
> I would still like you to show this mythical piece of software that needs
> this compatibility.
>
> -eric
>
> On Jan 8, 2014 3:06 AM, "Bernie Ogden" <bogden at arm.com>
wrote:
>
> I think there's an error in the example here.
> http://gcc.gnu.org/onlinedocs/gcc-4.8.2/gcc/AArch64-Options.html still
> documents -mcpu, and that march does not take CPUs as arguments. A local
> GCC developer tells me that the documentation is wrong in that -mcpu is
> actually a shorthand for specifying both -mtune and -march, but that the
> option is certainly there.
>
>
>
> If we want GCC comptability then that's what we have to do, unless
someone
> knows that GCC ARM/AArch64 is actually going to move away from this.
>
>
>
> Do we want GCC compatibility?
>
>
>
> Regards,
>
>
>
> Bernie
>
>
>
>
>
> *From:* cfe-dev-bounces at cs.uiuc.edu [mailto:cfe-dev-bounces at
cs.uiuc.edu] *On
> Behalf Of *Eric Christopher
> *Sent:* 07 January 2014 21:37
> *To:* Renato Golin; Amara Emerson; Clang Dev; LLVM Dev
> *Subject:* Re: [cfe-dev] [LLVMdev] AArch64 Clang CLI interface proposal
>
>
>
> Parsing the arch string is a bit icky, but I don't really have too much
of
> a problem with it - and it's better than -mcpu so...
>
>
>
> -eric
>
>
>
> On Tue Jan 07 2014 at 9:23:43 AM, Renato Golin <renato.golin at
linaro.org>
> wrote:
>
>   On 7 January 2014 17:05, Amara Emerson <amara.emerson at arm.com>
wrote:
>
> We plan on implementing this interface for AArch64 Clang in future, and
> completely dropping the current support for -mfpu. This means that -march
> will become the preferred way to specify the target CPU/architecture.
>
>
>
> Hi Amara,
>
>
>
> This is something we were converging on the ARM32 world, too, and I
> believe other targets would probably do the same, if not before us.
> Hopefully, that'd also help clean up the driver's code in the
process.
>
>
>
> cheers,
>
> --renato
>
>
> -- IMPORTANT NOTICE: The contents of this email and any attachments are
> confidential and may also be privileged. If you are not the intended
> recipient, please notify the sender immediately and do not disclose the
> contents to any other person, use it for any purpose, or store or copy the
> information in any medium. Thank you.
>
> ARM Limited, Registered office 110 Fulbourn Road, Cambridge CB1 9NJ,
> Registered in England & Wales, Company No: 2557590
> ARM Holdings plc, Registered office 110 Fulbourn Road, Cambridge CB1 9NJ,
> Registered in England & Wales, Company No: 2548782
>
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Shrug, my concern was the ridiculous arm32 version. If you want a confusing
duplicate option for setting both when just march should do then knock
yourself out.
On Jan 8, 2014 4:34 AM, "Bernie Ogden" <bogden at arm.com>
wrote:
> I'm just stating that _if_ GCC compatibility is desired then we have to
> have -mcpu.
>
>
>
> I don't think there's software that *needs* the compatibility, but
it is
> easier for GCC projects to switch to clang if that compatibility is there -
> which I think is why we go for GCC compatibility in the first place?
>
>
>
> (I raised http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59718 on the GCC
> docs.)
>
>
>
>
>
> *From:* Eric Christopher [mailto:echristo at gmail.com]
> *Sent:* 08 January 2014 12:23
> *To:* Bernard Ogden
> *Cc:* Renato Golin; LLVM Developers Mailing List; Clang Dev; Amara Emerson
> *Subject:* RE: [cfe-dev] [LLVMdev] AArch64 Clang CLI interface proposal
>
>
>
> I knew I'd regret leaving that option in for the MIPS port back in 99.
> Basically this is the only acceptable way for mcpu to exist, but should
> never have been added to the GCC aarch64 port at all since there's no
> compatibility with existing build systems to worry about.
>
> I would still like you to show this mythical piece of software that needs
> this compatibility.
>
> -eric
>
> On Jan 8, 2014 3:06 AM, "Bernie Ogden" <bogden at arm.com>
wrote:
>
> I think there's an error in the example here.
> http://gcc.gnu.org/onlinedocs/gcc-4.8.2/gcc/AArch64-Options.html still
> documents -mcpu, and that march does not take CPUs as arguments. A local
> GCC developer tells me that the documentation is wrong in that -mcpu is
> actually a shorthand for specifying both -mtune and -march, but that the
> option is certainly there.
>
>
>
> If we want GCC comptability then that's what we have to do, unless
someone
> knows that GCC ARM/AArch64 is actually going to move away from this.
>
>
>
> Do we want GCC compatibility?
>
>
>
> Regards,
>
>
>
> Bernie
>
>
>
>
>
> *From:* cfe-dev-bounces at cs.uiuc.edu [mailto:cfe-dev-bounces at
cs.uiuc.edu] *On
> Behalf Of *Eric Christopher
> *Sent:* 07 January 2014 21:37
> *To:* Renato Golin; Amara Emerson; Clang Dev; LLVM Dev
> *Subject:* Re: [cfe-dev] [LLVMdev] AArch64 Clang CLI interface proposal
>
>
>
> Parsing the arch string is a bit icky, but I don't really have too much
of
> a problem with it - and it's better than -mcpu so...
>
>
>
> -eric
>
>
>
> On Tue Jan 07 2014 at 9:23:43 AM, Renato Golin <renato.golin at
linaro.org>
> wrote:
>
> On 7 January 2014 17:05, Amara Emerson <amara.emerson at arm.com>
wrote:
>
> We plan on implementing this interface for AArch64 Clang in future, and
> completely dropping the current support for -mfpu. This means that -march
> will become the preferred way to specify the target CPU/architecture.
>
>
>
> Hi Amara,
>
>
>
> This is something we were converging on the ARM32 world, too, and I
> believe other targets would probably do the same, if not before us.
> Hopefully, that'd also help clean up the driver's code in the
process.
>
>
>
> cheers,
>
> --renato
>
>
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Ah and thanks for the GCC bug. That should help clarify matters.

I assume that big. LITTLE support is coming as well in the option parser?
On Jan 8, 2014 4:34 AM, "Bernie Ogden" <bogden at arm.com>
wrote:
> I'm just stating that _if_ GCC compatibility is desired then we have to
> have -mcpu.
>
>
>
> I don't think there's software that *needs* the compatibility, but
it is
> easier for GCC projects to switch to clang if that compatibility is there -
> which I think is why we go for GCC compatibility in the first place?
>
>
>
> (I raised http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59718 on the GCC
> docs.)
>
>
>
>
>
> *From:* Eric Christopher [mailto:echristo at gmail.com]
> *Sent:* 08 January 2014 12:23
> *To:* Bernard Ogden
> *Cc:* Renato Golin; LLVM Developers Mailing List; Clang Dev; Amara Emerson
> *Subject:* RE: [cfe-dev] [LLVMdev] AArch64 Clang CLI interface proposal
>
>
>
> I knew I'd regret leaving that option in for the MIPS port back in 99.
> Basically this is the only acceptable way for mcpu to exist, but should
> never have been added to the GCC aarch64 port at all since there's no
> compatibility with existing build systems to worry about.
>
> I would still like you to show this mythical piece of software that needs
> this compatibility.
>
> -eric
>
> On Jan 8, 2014 3:06 AM, "Bernie Ogden" <bogden at arm.com>
wrote:
>
> I think there's an error in the example here.
> http://gcc.gnu.org/onlinedocs/gcc-4.8.2/gcc/AArch64-Options.html still
> documents -mcpu, and that march does not take CPUs as arguments. A local
> GCC developer tells me that the documentation is wrong in that -mcpu is
> actually a shorthand for specifying both -mtune and -march, but that the
> option is certainly there.
>
>
>
> If we want GCC comptability then that's what we have to do, unless
someone
> knows that GCC ARM/AArch64 is actually going to move away from this.
>
>
>
> Do we want GCC compatibility?
>
>
>
> Regards,
>
>
>
> Bernie
>
>
>
>
>
> *From:* cfe-dev-bounces at cs.uiuc.edu [mailto:cfe-dev-bounces at
cs.uiuc.edu] *On
> Behalf Of *Eric Christopher
> *Sent:* 07 January 2014 21:37
> *To:* Renato Golin; Amara Emerson; Clang Dev; LLVM Dev
> *Subject:* Re: [cfe-dev] [LLVMdev] AArch64 Clang CLI interface proposal
>
>
>
> Parsing the arch string is a bit icky, but I don't really have too much
of
> a problem with it - and it's better than -mcpu so...
>
>
>
> -eric
>
>
>
> On Tue Jan 07 2014 at 9:23:43 AM, Renato Golin <renato.golin at
linaro.org>
> wrote:
>
> On 7 January 2014 17:05, Amara Emerson <amara.emerson at arm.com>
wrote:
>
> We plan on implementing this interface for AArch64 Clang in future, and
> completely dropping the current support for -mfpu. This means that -march
> will become the preferred way to specify the target CPU/architecture.
>
>
>
> Hi Amara,
>
>
>
> This is something we were converging on the ARM32 world, too, and I
> believe other targets would probably do the same, if not before us.
> Hopefully, that'd also help clean up the driver's code in the
process.
>
>
>
> cheers,
>
> --renato
>
>
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On 8 January 2014 12:32, Bernard Ogden <Bernard.Ogden at arm.com> wrote:
>  I don't think there's software that *needs* the compatibility, but
it is
> easier for GCC projects to switch to clang if that compatibility is there -
> which I think is why we go for GCC compatibility in the first place?
>
Hi Bernie,

GCC compatibility is always considered to be an important feature of LLVM,
not the *most* important one. We'll never go beyond reason to add GCC
compatibility just because, especially one that is poorly or not at all
documented.

The general rule of thumb is to ask the questions:
 * Do we really need it?
 * Isn't there any other way?
 * Is this sane? Or should the original authors re-write their programs?

There has been some progress on both GCC and LLVM to co-operate, rather
than follow each other blindly, and I can see this as the only future for
both toolchains.

In this specific case, I'd strongly oppose to follow whatever GCC does,
since the Clang driver is already mind bogging. The only reasonable course
of action from here is to open the discussion in the GCC and LLVM community
together (not sure how, but we'll *have* to figure it out), and follow from
there.

cheers,
--renato
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Eric Christopher <echristo at gmail.com> writes:
> I knew I'd regret leaving that option in for the MIPS port back in 99.
It didn't last long :-)  -mcpu for MIPS went away in 2002.

Thanks,
Richard