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

[Adam Nemet via llvm-dev]

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 <mailto: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 <mailto: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 <mailto: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 <mailto: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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