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

It isn't relevant, really, Matt just brought up "llc --version" as
a way to
show the default triple and native cpu.
The same question ("Which TTI do/should we get with -mcpu=generic / when
not providing -mcpu at all") applies to opt.

On Fri, Dec 2, 2016 at 9:53 AM, Adam Nemet <anemet at apple.com> wrote:
> Why is llc relevant to this thread, is this just an aside?
> Target-independent tests for LV are formulated with opt.
>
> On Nov 30, 2016, at 11:53 AM, Michael Kuperstein via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> Yeah, this makes a lot of sense, -mcpu=generic (as opposed to
> -mcpu=native) is the sane default.
> I guess I was just expecting an x86 host to get a "generic x86
TTI"
> (whatever that means), not a "generic TTI".
>
> On Wed, Nov 30, 2016 at 11:49 AM, Matthew Simpson <mssimpso at
codeaurora.org
> > wrote:
>
>> 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
>>>
>>>
>>
> _______________________________________________
> 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/20161202/590e4ac0/attachment.html>

On Fri, Dec 2, 2016 at 1:30 PM, Michael Kuperstein via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> It isn't relevant, really, Matt just brought up "llc
--version" as a way
> to show the default triple and native cpu.
> The same question ("Which TTI do/should we get with -mcpu=generic /
when
> not providing -mcpu at all") applies to opt.
>
And just to be clear in case there was any confusion, in opt when a target
is not specified we get the generic TTI, not one for the host or default
triple indicated by llc. I think this was Adam's original point/question.
As long as the tests we want to remain target-independent don't specify a
target triple, we should get the same generic TTI on any host.

-- Matt
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20161202/9739177b/attachment.html>

> On Dec 2, 2016, at 11:06 AM, Matthew Simpson <mssimpso at
codeaurora.org> wrote:
> 
> 
> On Fri, Dec 2, 2016 at 1:30 PM, Michael Kuperstein via llvm-dev
<llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>>
wrote:
> It isn't relevant, really, Matt just brought up "llc
--version" as a way to show the default triple and native cpu.
> The same question ("Which TTI do/should we get with -mcpu=generic /
when not providing -mcpu at all") applies to opt.
> 
> And just to be clear in case there was any confusion, in opt when a target
is not specified we get the generic TTI, not one for the host or default triple
indicated by llc. I think this was Adam's original point/question. As long
as the tests we want to remain target-independent don't specify a target
triple, we should get the same generic TTI on any host.
Yes opt an llc are completely different in this regard.  llc always needs a
target to generate code for.  opt does not, it uses data layout and TTI (the
default if not target is specified).

That is why I think bringing llc into the discussion was confusing, at least I
think it confused Renato.  My whole point was that you can write
target-independent tests with *opt* but not with llc of course (which I think
was Renato’s conclusion).

Adam
> 
> -- Matt
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20161202/7931d478/attachment.html>