llvm dev - Jul 2016 - difference between llvm-gcc and clang

Hi everyone,

Both llvm-gcc and clang would use llvm as its backend. Dose everyone know the
difference of bitcode generated by llvm-gcc and llvm? Or actually they are same,
like if I use the same compiler options, like -O4.

Any help is appreciated.

Best,
Yuxi
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On 21 July 2016 at 14:02, Yuxi Chen via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Both llvm-gcc and clang would use llvm as its backend. Dose everyone know
> the difference of bitcode generated by llvm-gcc and llvm?
llvm-gcc used to be a compiler that used the GCC front-end (C parser
etc) to generate LLVM IR and then used the LLVM backends. It's a
long-abandoned project now though (not updated past GCC 4.2), with all
effort going into Clang (or GCC proper!).

You're only even likely to find traces of it on macOS, where
/usr/bin/llvm-gcc exists for backwards-compatibility reasons. However,
that's not really llvm-gcc any more, it's just another way to run
Clang.
> Or actually they are same, like if I use the same compiler options, like
-O4.
You shouldn't be using -O4. At one point I think it was a weird way to
trigger LTO (now you'd use -flto), but it's now only accepted for
compatibility and means the same thing as -O3. It gives you a warning
if you try to use it.

Cheers.

Tim.

llvm-gcc is obsolete, It was only an intermediate step to where we are
today.

On Fri, Jul 22, 2016 at 9:02 AM, Yuxi Chen via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hi everyone,
>
> Both llvm-gcc and clang would use llvm as its backend. Dose everyone know
> the difference of bitcode generated by llvm-gcc and llvm? Or actually they
> are same, like if I use the same compiler options, like -O4.
>
> Any help is appreciated.
>
> Best,
> Yuxi
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
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Hi Tim, 

Thanks for your reply. 
I know O4 is same as O3 now. I am wondering the bitcodes generated by llvm-gcc
and clang  are same, or almost same, I mean they are almost same, but maybe some
newly-created  optimization would exert impact.

Best,
Yuxi
________________________________________
From: Tim Northover [t.p.northover at gmail.com]
Sent: Thursday, July 21, 2016 4:11 PM
To: Yuxi Chen
Cc: llvmdev at cs.uiuc.edu; llvm-dev at lists.llvm.org; llvmdev-bounces at
cs.uiuc.edu
Subject: Re: [llvm-dev] difference between llvm-gcc and clang

On 21 July 2016 at 14:02, Yuxi Chen via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Both llvm-gcc and clang would use llvm as its backend. Dose everyone know
> the difference of bitcode generated by llvm-gcc and llvm?
llvm-gcc used to be a compiler that used the GCC front-end (C parser
etc) to generate LLVM IR and then used the LLVM backends. It's a
long-abandoned project now though (not updated past GCC 4.2), with all
effort going into Clang (or GCC proper!).

You're only even likely to find traces of it on macOS, where
/usr/bin/llvm-gcc exists for backwards-compatibility reasons. However,
that's not really llvm-gcc any more, it's just another way to run
Clang.
> Or actually they are same, like if I use the same compiler options, like
-O4.
You shouldn't be using -O4. At one point I think it was a weird way to
trigger LTO (now you'd use -flto), but it's now only accepted for
compatibility and means the same thing as -O3. It gives you a warning
if you try to use it.

Cheers.

Tim.

Thanks for your reply.

Yuxi
________________________________
From: bruce.hoult at gmail.com [bruce.hoult at gmail.com] on behalf of Bruce
Hoult [bruce at hoult.org]
Sent: Thursday, July 21, 2016 4:12 PM
To: Yuxi Chen
Cc: llvmdev at cs.uiuc.edu; llvm-dev at lists.llvm.org; llvmdev-bounces at
cs.uiuc.edu
Subject: Re: [llvm-dev] difference between llvm-gcc and clang

llvm-gcc is obsolete, It was only an intermediate step to where we are today.

On Fri, Jul 22, 2016 at 9:02 AM, Yuxi Chen via llvm-dev <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
Hi everyone,

Both llvm-gcc and clang would use llvm as its backend. Dose everyone know the
difference of bitcode generated by llvm-gcc and llvm? Or actually they are same,
like if I use the same compiler options, like -O4.

Any help is appreciated.

Best,
Yuxi

_______________________________________________
LLVM Developers mailing list
llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev


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