[LLVMdev] Simple Loop Vectorize Question

Nadav Rotem nrotem at apple.com
Thu May 9 22:27:24 PDT 2013

Hi Josh, 

This line works for me:

opt file.ll -loop-vectorize -S -o - -mtriple=x86_64 -mcpu=corei7-avx -debug

You need to specify the triple on the command line if it is not inside the module. 


On May 9, 2013, at 5:53 PM, Joshua Klontz <josh.klontz at gmail.com> wrote:

> Nadav,
> Please forgive my ignorance, but 'opt -mcpu=corei7 -loop-vectorize -S -debug double.ll' doesn't appear to make a difference. In fact it seems to be ignored as garbage values for -mcpu don't raise an error. Am I overlooking something else also?
> Many Thanks,
> Josh
> On Thu, May 9, 2013 at 6:06 PM, Nadav Rotem <nrotem at apple.com> wrote:
> Hi Josh, 
> Your modules does not have a triple, so the target machine and TargetTransformInfo have no way of knowing if you are running on a machine with vector registers.  Try adding the '-mcpu=XXXX' to opt and see what happens. 
> Thanks,
> Nadav
> On May 9, 2013, at 1:42 PM, Josh Klontz <josh.klontz at gmail.com> wrote:
>> Hi! I am trying to get the loop vectorizer to work on a simple example
>> (http://pastebin.com/tGhpc4y0) that doubles every element in a vector.
>> I've found that 'opt -loop-vectorize -force-vector-width=4 -S -debug
>> double.ll' works as expected. However, removing the -force-vector-width flag
>> results in no vectorization. From the debug output I can see that the issue
>> boils down to:
>> LV: The Widest type: 32 bits.
>> LV: The Widest register is:32bits.
>> I tried to work back through the source code to figure out why the widest
>> register is incorrect, though I get lost following the code logic for how
>> TargetTransformInfo gets initialized. Therefore, I have two questions:
>> 1) Can -force-vector-width be specified from the C++ API? And if so, how?
>> 2) What am I neglecting to do so that TargetTransformInfo is set correctly
>> and vectorization happens without forcing a vector width? Ultimately I would
>> like use vectorization in conjunction with the JIT ExecutionEngine.
>> Thank you to those of you who have answered my questions in the past, the
>> answers have helped tremendously and I am extremely grateful!
>> Kindly,
>> Josh
>> --
>> View this message in context: http://llvm.1065342.n5.nabble.com/Simple-Loop-Vectorize-Question-tp57584.html
>> Sent from the LLVM - Dev mailing list archive at Nabble.com.
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