[llvm-dev] Loop Vectorize: Testing cost model driven transformations

[Michael Kuperstein via llvm-dev]

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
>>>>
>>>
>>>
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>>>
>>>
>>
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