Conditional moves vs. branching in unrolled loops

[Paul Sandoz]

> On 6 Jan 2016, at 11:12, Paul Sandoz <Paul.Sandoz at oracle.com> wrote:

> At least for this set of tests the results indicate conditional moves offer no major advantage over branching. For the worst case branching scenario (the “50 cent” case) conditional moves appear marginally better, but as you say the data pattern is likely rare.

Scrap that, cmoves are kicking for "A.forTest_if     0.5  RANDOM_RAMP_UP"

Disabling them with -XX:ConditionalMoveLimit==0 (thanks Roland), muddies the waters a bit:
# VM options: -XX:-TieredCompilation
Benchmark     (bias)            (dg)  (size)  Mode  Cnt     Score     Error  Units
A.forTest_if     0.1  RANDOM_RAMP_UP       1  avgt    5     3.535 ±   0.083  ns/op
A.forTest_if     0.1  RANDOM_RAMP_UP      10  avgt    5     7.478 ±   0.232  ns/op
A.forTest_if     0.1  RANDOM_RAMP_UP     100  avgt    5    42.348 ±   0.922  ns/op
A.forTest_if     0.1  RANDOM_RAMP_UP    1000  avgt    5   460.924 ±  12.692  ns/op
A.forTest_if     0.1  RANDOM_RAMP_UP   10000  avgt    5  3708.576 ± 110.138  ns/op
A.forTest_if     0.5  RANDOM_RAMP_UP       1  avgt    5     3.557 ±   0.172  ns/op
A.forTest_if     0.5  RANDOM_RAMP_UP      10  avgt    5     9.860 ±   0.135  ns/op
A.forTest_if     0.5  RANDOM_RAMP_UP     100  avgt    5    82.380 ±   1.971  ns/op
A.forTest_if     0.5  RANDOM_RAMP_UP    1000  avgt    5   832.391 ±  23.629  ns/op
A.forTest_if     0.5  RANDOM_RAMP_UP   10000  avgt    5  8325.406 ± 206.872  ns/op


# VM options: -XX:ConditionalMoveLimit=0 -XX:-TieredCompilation
Benchmark     (bias)            (dg)  (size)  Mode  Cnt      Score     Error  Units
A.forTest_if     0.1  RANDOM_RAMP_UP       1  avgt    5      3.554 ±   0.049  ns/op
A.forTest_if     0.1  RANDOM_RAMP_UP      10  avgt    5      9.382 ±   0.062  ns/op
A.forTest_if     0.1  RANDOM_RAMP_UP     100  avgt    5     37.483 ±   0.696  ns/op
A.forTest_if     0.1  RANDOM_RAMP_UP    1000  avgt    5    369.375 ±   9.780  ns/op
A.forTest_if     0.1  RANDOM_RAMP_UP   10000  avgt    5   3712.492 ± 128.310  ns/op
A.forTest_if     0.5  RANDOM_RAMP_UP       1  avgt    5      3.546 ±   0.053  ns/op
A.forTest_if     0.5  RANDOM_RAMP_UP      10  avgt    5      7.488 ±   0.118  ns/op
A.forTest_if     0.5  RANDOM_RAMP_UP     100  avgt    5     52.889 ±   5.328  ns/op
A.forTest_if     0.5  RANDOM_RAMP_UP    1000  avgt    5    447.437 ±  14.273  ns/op
A.forTest_if     0.5  RANDOM_RAMP_UP   10000  avgt    5  10040.920 ± 993.644  ns/op
Paul.
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