llvm dev - Nov 2016 - Loop Vectorize: Testing cost model driven transformations

On Wed, Nov 30, 2016 at 1:04 PM, Michael Kuperstein via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> So, just to make sure I understand, what is getting a specific TTI in llc
> triggered off? -mcpu?

Right, TTI would be determined by the target specified in the IR or set
explicitly with the -m flags. My understanding is that if the target is
left unspecified in the IR and not set with the -m flags, llc will generate
code for the default target listed in the output of "llc --version".

-- Matt
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20161130/7523c735/attachment.html>

Right, let's say what we get from llc --version is:

  Default target: x86_64-unknown-linux-gnu
  Host CPU: haswell

So, what we currently do is use the default target (which is normally the
host target), but ignore the host cpu?

Michael

On Wed, Nov 30, 2016 at 10:58 AM, Matthew Simpson <mssimpso at
codeaurora.org>
wrote:
>
> On Wed, Nov 30, 2016 at 1:04 PM, Michael Kuperstein via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> So, just to make sure I understand, what is getting a specific TTI in
llc
>> triggered off? -mcpu?
>
>
> Right, TTI would be determined by the target specified in the IR or set
> explicitly with the -m flags. My understanding is that if the target is
> left unspecified in the IR and not set with the -m flags, llc will generate
> code for the default target listed in the output of "llc
--version".
>
> -- Matt
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20161130/8b6774d0/attachment.html>

That's right. In your example, if the target isn't specified anywhere,
an
llc invocation would be equivalent to "llc
-mtriple=x86_64-unknown-linux-gnu -mcpu=generic". TTI queries (in e.g.,
CodeGenPrepare) would be based on this. From opt, if the target triple is
left unspecified, we will use the "base" TTI implementation (not x86).

-- Matt

On Wed, Nov 30, 2016 at 2:07 PM, Michael Kuperstein via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Right, let's say what we get from llc --version is:
>
>   Default target: x86_64-unknown-linux-gnu
>   Host CPU: haswell
>
> So, what we currently do is use the default target (which is normally the
> host target), but ignore the host cpu?
>
> Michael
>
> On Wed, Nov 30, 2016 at 10:58 AM, Matthew Simpson <mssimpso at
codeaurora.org
> > wrote:
>
>>
>> On Wed, Nov 30, 2016 at 1:04 PM, Michael Kuperstein via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>> So, just to make sure I understand, what is getting a specific TTI
in
>>> llc triggered off? -mcpu?
>>
>>
>> Right, TTI would be determined by the target specified in the IR or set
>> explicitly with the -m flags. My understanding is that if the target is
>> left unspecified in the IR and not set with the -m flags, llc will
generate
>> code for the default target listed in the output of "llc
--version".
>>
>> -- Matt
>>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20161130/d7d7df91/attachment.html>