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

[Michael Kuperstein via llvm-dev]

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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