Chandler Carruth 424b2b0093 [vectorizer] Teach the loop vectorizer's unroller to only unroll by ... powers of two. This is essentially always the correct thing given the impact on alignment, scaling factors that can be used in addressing modes, etc. Also, fix the management of the unroll vs. small loop cost to more accurately model things with this world. Enhance a test case to actually exercise more of the unroll machinery if using synthetic constants rather than a specific target model. Before this change, with the added flags this test will unroll 3 times instead of either 2 or 4 (the two sensible answers). While I don't expect this to make a huge difference, if there are lots of loops sitting right on the edge of hitting the 'small unroll' factor, they might change behavior. However, I've benchmarked moving the small loop cost up and down in many various ways and by a huge factor (2x) without seeing more than 0.2% code size growth. Small adjustments such as the series that led up here have led to about 1% improvement on some benchmarks, but it is very close to the noise floor so I mostly checked that nothing regressed. Let me know if you see bad behavior on other targets but I don't expect this to be a sufficiently dramatic change to trigger anything. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200213 91177308-0d34-0410-b5e6-96231b3b80d8		2014-01-27 11:12:24 +00:00
..
llvm	[vectorizer] Teach the loop vectorizer's unroller to only unroll by	2014-01-27 11:12:24 +00:00
llvm-c	Fix known typos	2014-01-24 17:20:08 +00:00