On 2012/06/14 09:53:59, danno wrote:
In general, this isn't a good idea. AFAICT, you can't be sure that an
HElementsTransition dominates all of the uses of its inputs. It might
work for
this benchmark, but I can think of straight-forward situations where this
won't
be the case.
I meant to replace the uses within the pre-header of loop, only for hoisted
instructions.
In current code, I let it start from block start, as I didn't think of cases
where it could be wrong.
Furthermore, some instructions that depend on the input to the
HElementsTransition, like simple property Loads and Stores, may not
benefit
from
depending on the HTransition. It will prevent them from being hoisted
into an
outer loop beyond the inner loop's preheader by doing this.
Yes, the fixup should be served in a seperate loop after one pass of hoist.
Probably also not
the right thing to do.
Could you please elaborate it a little?
What is the motivation of the change? If we are missing GVN opportunities
for
selected instructions because they should be treated equivalently
regardless
whether they depend on a HElementsTransition or the inputs to the
HElementsTransition, then the Equal method of those affected instructions
should
be modified appropriately to handle those cases.
It's something like this: (part of a pre-header, all of these are hoised
instructions)
[t235 t237 i295] should be same as [t207 t209 i289]
...
1 t206 TransitionElementsKind t166 [FAST_HOLEY_SMI_ELEMENTS] ->
[FAST_HOLEY_DOUBLE_ELEMENTS]
changes[NewSpacePromotion,ElementsKind,ElementsPointer]
1 t207 CheckMaps t166 [0x3d508da1]
1 t209 JSArrayLength t166 t207
2 i289 Change t209 t to i range[-2147483648,2147483647,m0=0]
1 d290 Constant 0x46c93e35 <Number: 0.3>
1 d292 Constant 0x46c93e41 <Number: 0.59>
1 d294 Constant 0x46c93e4d <Number: 0.11>
6 t208 LoadElements t166
1 t235 CheckMaps t166 [0x3d508da1]
1 t237 JSArrayLength t166 t235
2 i295 Change t237 t to i range[-2147483648,2147483647,m0=0]
== END of Block ==
http://codereview.chromium.org/10544133/
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