[llvm-dev] SCEV LoopTripCount

[Alexandre Isoard via llvm-dev]

Hello,

I was doing some experiments with SCEV and especially the loop trip count.
Sorry for the dumb question, what is the easiest way to dump SCEV analysis
results on a .bc file?

On a side note, I wanted to see if we could optimize this function:

unsigned long kernel(long w, long h, long d) {
unsigned long count = 0;
for(int i = 0; i < w; ++i)
for(int j = i; j < h; ++j)
for(int k = j; k < d; ++k)
++count;
return count;
}

into this (it might not take into account overflows, it was generated using
the barvinok library):

unsigned long kernel2(long w, long h, long d) {
return
(-1 + w >= 0 && -1 - w + h >= 0 && -1 - h + d >= 0)
? (((((2 * w - 3 * w*w + w*w*w) + 3 * w * h + -3 * w * h*h) + ((3 * w - 3 *
w*w) + 6 * w * h) * d))/6)
: (-1 + w >= 0 && -1 - w + d >= 0 && h - d >= 0)
? ((((2 * w - 3 * w*w + w*w*w) + (6 * w - 3 * w*w) * d + 3 * w * d*d))/6)
: (-1 + h >= 0 && w - h >= 0 && -1 - h + d >= 0)
? ((((2 * h - 2 * h*h*h) + (3 * h + 3 * h*h) * d))/6)
: (-1 + d >= 0 && h - d >= 0 && w - d >= 0)
? (((2 * d + 3 * d*d + d*d*d))/6)
: 0;
}

I am not sure how advanced are SCEV-based trip counts.

Best regards.

-- 
*Alexandre Isoard*
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20160809/805a72bf/attachment.html>