[turbofan] Reduce some Float64 division to multiplication

[turbofan] Reduce some Float64 division to multiplication

For denominators that are powers of two, replace Float64 division with
multiplication by the reciprocal.

Additionally, replace division by -1 with negation, and multiplication by two
with addition.

BUG=

Committed: https://crrev.com/5ae2d0e58abd54bc51421bf7cd129d08f72a2346
Cr-Commit-Position: refs/heads/master@{#39478}

[martyn.capewell, 2016-09-15 13:03:07]

martyn.capewell@arm.com changed reviewers:
+ bmeurer@chromium.org, epertoso@chromium.org

[Benedikt Meurer, 2016-09-15 17:20:52]

https://codereview.chromium.org/2347573002/diff/1/src/compiler/machine-operat...
File src/compiler/machine-operator-reducer.cc (right):

https://codereview.chromium.org/2347573002/diff/1/src/compiler/machine-operat...
src/compiler/machine-operator-reducer.cc:415: if (m.right().Is(2)) {            
                    // x * 2.0 => x + x
This should come after the m.IsFoldable case below.

https://codereview.chromium.org/2347573002/diff/1/src/compiler/machine-operat...
src/compiler/machine-operator-reducer.cc:431: if (m.right().Is(-1)) {           
                    // x / -1.0 => -x
Move this below the m.IsFoldable case.

https://codereview.chromium.org/2347573002/diff/1/src/compiler/machine-operat...
src/compiler/machine-operator-reducer.cc:446: Double k =
Double(m.right().Value());
Can you add this as a IsPowerOfTwo methd to the Float64Matcher?
Also what is the rationale to do this for power of two?

[martyn.capewell, 2016-09-15 17:41:20]

https://codereview.chromium.org/2347573002/diff/1/src/compiler/machine-operat...
File src/compiler/machine-operator-reducer.cc (right):

https://codereview.chromium.org/2347573002/diff/1/src/compiler/machine-operat...
src/compiler/machine-operator-reducer.cc:446: Double k =
Double(m.right().Value());
On 2016/09/15 17:20:52, Benedikt Meurer wrote:
> Also what is the rationale to do this for power of two?

The idea is that all reciprocals of non-denormal powers of two can be
represented exactly, and are quick to identify, so any division by a power of
two can be reduced to a multiplication by its reciprocal and still give the same
result. I can add this as a comment.

[Benedikt Meurer, 2016-09-15 18:20:05]

https://codereview.chromium.org/2347573002/diff/1/src/compiler/machine-operat...
File src/compiler/machine-operator-reducer.cc (right):

https://codereview.chromium.org/2347573002/diff/1/src/compiler/machine-operat...
src/compiler/machine-operator-reducer.cc:446: Double k =
Double(m.right().Value());
Aye, thanks. Please add a comment.

[Benedikt Meurer, 2016-09-16 17:19:28]

lgtm

[martyn.capewell, 2016-09-16 17:21:53]

The CQ bit was checked by martyn.capewell@arm.com

[commit-bot: I haz the power, 2016-09-16 17:22:00]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-09-16 17:55:09]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-09-16 17:55:36]

Description was changed from

==========
[turbofan] Reduce some Float64 division to multiplication

For denominators that are powers of two, replace Float64 division with
multiplication by the reciprocal.

Additionally, replace division by -1 with negation, and multiplication by two
with addition.

BUG=
==========

to

==========
[turbofan] Reduce some Float64 division to multiplication

For denominators that are powers of two, replace Float64 division with
multiplication by the reciprocal.

Additionally, replace division by -1 with negation, and multiplication by two
with addition.

BUG=

Committed: https://crrev.com/5ae2d0e58abd54bc51421bf7cd129d08f72a2346
Cr-Commit-Position: refs/heads/master@{#39478}
==========

[commit-bot: I haz the power, 2016-09-16 17:55:37]

Patchset 2 (id:??) landed as
https://crrev.com/5ae2d0e58abd54bc51421bf7cd129d08f72a2346
Cr-Commit-Position: refs/heads/master@{#39478}