On 2015/08/27 19:55:36, Michael Starzinger wrote:
https://codereview.chromium.org/1321663003/diff/40001/test/cctest/interpreter/test-bytecode-generator.cc
File test/cctest/interpreter/test-bytecode-generator.cc (right):
https://codereview.chromium.org/1321663003/diff/40001/test/cctest/interpreter/test-bytecode-generator.cc#newcode257
test/cctest/interpreter/test-bytecode-generator.cc:257: { 3.14, 3.14 }
On 2015/08/27 19:36:29, Michael Starzinger wrote:
> On 2015/08/27 16:34:07, rmcilroy wrote:
> > Michi - looks like double literals aren't de-duped by the parser (we
get a
new
> > HeapNumber each time). Is this done elsewhere or have we always had a
new
> > HeapNumber for each double literal?
>
> Not sure I understand your comment correctly. How would the parser
de-dupe
> literals? That would make the AST degenerate into a DAG if we would do
that.
Or
> am I missing something here?
>
> Compilers can de-dupe the values. One mechanism of de-duping would be
GVN
which
> makes sure that identical nodes in the graph are coalesced. Both
Hydrogen
and
> TurboFan do that.
Ah, I think now I understand where you are coming from, I think your
question
was whether AstValue::Internalize should canonicalize HeapNumbers or not.
Maeh,
the data-structure for canonicalizing them would probably end up eating
more
memory than the duped HeapNumbers, I don't think that would buy us
anything
besides complexity.
Rather the question is, why do we "internalize" double literals in the
first
place. One could argue that it should be the responsibility of the
compiler to
decide whether and where to allocate HeapNumbers. But that's opening a
can of
worms. I suggest we don't go there.
The JSGraph in TurboFan de-dupes all constants (including HeapNumbers),
except
other HeapObjects. I agree with Michi that the parser shouldn't try to
de-dup
doubles; it's probably not worth it.
https://codereview.chromium.org/1321663003/
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