[LLVMdev] [cfe-dev] AArch64 Clang CLI interface proposal

Bernard Ogden Bernard.Ogden at arm.com
Wed Jan 8 04:32:32 PST 2014

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.

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?



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...


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.


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