llvm dev - Feb 2012 - [LLVMdev] Loop Unroll a constant number of times?

Is it possible to unroll a loop (forcibly if necessary) with llvm (possibly
the -loop-unroll pass) a constant number of times.

I believe that I read that the -unroll-count=x option was removed, correct?
So is there some other way to do this or is this just not possible in llvm?
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Ryan,
I see the following command line options in LoopUnrollPass.cpp:

static cl::opt<unsigned>
UnrollThreshold("unroll-threshold", cl::init(150), cl::Hidden,
  cl::desc("The cut-off point for automatic loop unrolling"));

static cl::opt<unsigned>
UnrollCount("unroll-count", cl::init(0), cl::Hidden,
  cl::desc("Use this unroll count for all loops, for testing
purposes"));

static cl::opt<bool>
UnrollAllowPartial("unroll-allow-partial", cl::init(false),
cl::Hidden,
  cl::desc("Allows loops to be partially unrolled until "
           "-unroll-threshold loop size is reached."));

static cl::opt<bool>
UnrollRuntime("unroll-runtime", cl::ZeroOrMore, cl::init(false),
cl::Hidden,
  cl::desc("Unroll loops with run-time trip counts"));

I assume the first two are most applicable to what you're trying to do. 
I've never used these options, so it would be a good idea to look at the
source to see what these are really doing.

Also, you'll probably need to put -mllvm before the argument to pass it to
the backend (clang -mllvm -unroll-threshold=10).

You can also use the -debug-only=loop-unroll option to get debug information. 
It too requires the -mllvm option.

Hope this helps,
  Chad


On Jan 31, 2012, at 5:16 PM, Ryan Taylor <ryta1203 at gmail.com> wrote:
> Is it possible to unroll a loop (forcibly if necessary) with llvm (possibly
the -loop-unroll pass) a constant number of times.
> 
> I believe that I read that the -unroll-count=x option was removed, correct?
So is there some other way to do this or is this just not possible in llvm?
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

On Jan 31, 2012, at 5:16 PM, Ryan Taylor <ryta1203 at gmail.com> wrote:
> Is it possible to unroll a loop (forcibly if necessary) with llvm (possibly
the -loop-unroll pass) a constant number of times.
> 
> I believe that I read that the -unroll-count=x option was removed, correct?
So is there some other way to do this or is this just not possible in llvm?
See clang -mllvm -help-hidden. If that doesn't work, llc -help-hidden.

Probably want something like -mllvm -unroll-runtime -mllvm -unroll-count=N. 

As with any experimental options, look at the source, and -mllvm
-debug-only=loop-unroll output to understand what it's doing.

Andy

Andrew,

  Thanks. Unfortunately, the runtime won't really work for what I'm
doing
but it seems that I can statically unroll just fine for the most part.

Thanks.

On Wed, Feb 1, 2012 at 8:38 AM, Andrew Trick <atrick at apple.com> wrote:
>
>
> On Jan 31, 2012, at 5:16 PM, Ryan Taylor <ryta1203 at gmail.com>
wrote:
>
> > Is it possible to unroll a loop (forcibly if necessary) with llvm
> (possibly the -loop-unroll pass) a constant number of times.
> >
> > I believe that I read that the -unroll-count=x option was removed,
> correct? So is there some other way to do this or is this just not possible
> in llvm?
>
> See clang -mllvm -help-hidden. If that doesn't work, llc -help-hidden.
>
> Probably want something like -mllvm -unroll-runtime -mllvm -unroll-count=N.
>
> As with any experimental options, look at the source, and -mllvm
> -debug-only=loop-unroll output to understand what it's doing.
>
> Andy
>
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