[PATCH] D21720: Unroll for uncountable loops

[Evgeny Stupachenko via Phabricator via llvm-commits]

evstupac added a comment.

Regarding performance data.
Initially I want unroll only loops where previous iteration value is reused. Just with this change I get the following.
197.parser up to 5% depending on CPU and 10% to 30% on set of internal benchmarks.
With xor and sub enabled most of benchmarks the results got buildsame or no performance change. However I still believe this fits to current functionality.

One thing I noticed, adding cost to regular unroll (not complete). All loops which counts something got unrolled:

while(smth)

  n++;

Use(n);

And unroll safes at least 1 instruction for such loops.


Repository:
  rL LLVM

https://reviews.llvm.org/D21720