On 2015/09/13 12:10:03, dougc wrote:
On 2015/04/20 12:20:40, titzer wrote:
>
https://codereview.chromium.org/1095063002/diff/1/src/compiler/js-typed-lowering.cc
> File src/compiler/js-typed-lowering.cc (right):
>
>
https://codereview.chromium.org/1095063002/diff/1/src/compiler/js-typed-lowering.cc#newcode373
> src/compiler/js-typed-lowering.cc:373: Reduction
> JSTypedLowering::ReduceBitwiseAnd(Node* node) {
> I think you want to move this optimization to machine-operator-reducer.
That
> will make it more general and also avoid the problem you see below.
Tried this suggestion, moving this to machine-operator-reducer. It works
in
part, but there are some issues that suggest this is too later to make
use of
this type information.
For example, for one error there is a bit-and operation being used that
appears
to be testing the low bit of a value that is the result of converting
true or
false to a number, which I presume is checking for a tagged number. The
type
information gives the input as having the range 0 to 1, so bit-and-ing
this
input with 1 is redundant and is eliminated. But the bit-and is being
applied
to
a lower level representation, to a tagged number, which is not the value
that
the type information applies to and this generates bad code. Does this
sound
right? Does it suggest another appropriate phase to perform transforms
that
depend on type information? Or should the transform be guarding against
being
applied to possibly tagger values?
Ah, yes. The range information is in terms of "semantic integer ranges" and
not
in terms of raw machine ranges. So the and's with 1 that you are seeing are
tag
checks. We will have to know the correct representation for this
optimization to
make sense.
https://codereview.chromium.org/1095063002/
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