[LLVMdev] Trying out Loop Vectorizer

Chandler Carruth chandlerc at google.com
Mon Dec 31 15:31:08 PST 2012

On Mon, Dec 31, 2012 at 3:26 PM, Nadav Rotem <nrotem at apple.com> wrote:

> On Dec 31, 2012, at 11:57 AM, Benjamin Kramer <benny.kra at gmail.com> wrote:
> I'm not entirely sure why this is the case, the target specific stuff for
> opt is still very new, but at the moment you have to explicitly set a
> triple for opt so it can access target-specific bits to estimate the cost
> of vectorization.
> I think that this is a good opportunity to discuss this topic.  At the
> moment 'opt' does not use the triple that is found in the module in order
> to initialize the backend and the backend related analysis passes. It
> relies on the '-mtriple' command line flag. LLC on the other hand uses the
> host triple. I see the following options:
> 1. 'opt' does not initialize the backend passes unless '-mtriple' is used.
> (the current option)
> 2. 'opt' grabs the triple from the bit code file and uses it to initialize
> the backend passes.
> 3. 'opt' gets the default target triple (like llc).

My only strong opinion is that I dislike #3.

I have a mild preference for encoding more in bitcode and less in
commandline switches, while still allowing commandline switches to override
what is in the bitcode.

> I think that Nick said that he prefers #2.
> Nadav
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