Commit Graph

98 Commits

Author SHA1 Message Date
johnmccutchan@google.com 08c99e80e6 Inline Float32x4 Getters
Review URL: https://codereview.chromium.org//13872020

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@21897 260f80e4-7a28-3924-810f-c04153c831b5
2013-04-23 17:52:10 +00:00
vegorov@google.com 1162595313 Convert EqualityCompare to StrictCompare if reciever is either null or guaranteed to have default equality operator.
R=srdjan@google.com
BUG=

Review URL: https://codereview.chromium.org//13878017

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@21696 260f80e4-7a28-3924-810f-c04153c831b5
2013-04-18 19:52:26 +00:00
vegorov@google.com 11edd87390 Convert diamond shaped control flow into a single conditional instruction.
Adds a IfConverter pass that right now recognizes two simple patterns cond ? 0 : 2^n and cond ? x : x+-1 that can be generated without branches on ia32 and x64 using setcc instruction.

R=fschneider@google.com

Review URL: https://codereview.chromium.org//14057004

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@21207 260f80e4-7a28-3924-810f-c04153c831b5
2013-04-10 15:09:46 +00:00
srdjan@google.com cbe8bd9a3a Restore r20998 with a bug fix: add field to guarded_fields_ when it contains relevant cid. Was missing most cases and did not check for unique adds.
Review URL: https://codereview.chromium.org//13726023

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@21008 260f80e4-7a28-3924-810f-c04153c831b5
2013-04-05 23:26:53 +00:00
srdjan@google.com e7f1ae5383 Revert r20998.
Review URL: https://codereview.chromium.org//13739002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@21001 260f80e4-7a28-3924-810f-c04153c831b5
2013-04-05 21:44:17 +00:00
srdjan@google.com 44938de19c Fix guarded_cid handling: add field to list of guarded_field at LoadField creation time.
Review URL: https://codereview.chromium.org//13529021

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@20998 260f80e4-7a28-3924-810f-c04153c831b5
2013-04-05 21:01:30 +00:00
fschneider@google.com 5e0ac1419e Use range analysis to improve constant propagation.
This CL runs a second round of constant propagation after range
analysis to eliminate additional unreachable code. Range analysis
is changed to mark branches as constant if the constraints they
generate are unsatisfiable.

The second pass of constant propagation only visits branches and
removes unreachable code, but does not do full constant propagation.

This proves useful when inlining array view operations where the
following pattern occurs:

for (i = 0; i < length; i++) {
  if (i < 0 || i >= length) {
    throw 123;
  }
  foo();
}

In this example the if-statement will be eliminated completely.

Also, fix a bug in range analyis where constraints of already
constrained values were missing.
Review URL: https://codereview.chromium.org//13469013

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@20914 260f80e4-7a28-3924-810f-c04153c831b5
2013-04-04 12:42:17 +00:00
srdjan@google.com 60e57ecfe1 Optimizes 'as' operation in similar way as 'instanceof': collect type feedback in unoptimized mode and try to convert it to a simple classcheck in optimized code.
Review URL: https://codereview.chromium.org//13190014

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@20783 260f80e4-7a28-3924-810f-c04153c831b5
2013-04-02 15:30:14 +00:00
vegorov@google.com 1c9d22d75c Collect type feedback for fields.
BUG=

Review URL: https://codereview.chromium.org//12529008

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@20235 260f80e4-7a28-3924-810f-c04153c831b5
2013-03-19 20:15:10 +00:00
fschneider@google.com 86da5111ad Replace scalarlist optimizations and split external array loads into two IL instructions.
This CL removes optimized access for scalarlist, and only the new TypedData classes
are optimized. I changed the runtime libraries core and math to use typedData
instead of scalarlist (Uint16List is used in StringBuffer, Uint32List by Math.random).

Instead of using LoadIndexed for internal and external arrays,
split external loads into a load of the backing store and a load
of the element.

v3 <- LoadIndexed(v1, index)

becomes

v2 <- LoadUntagged(v1, ExternalTypedData::data_offset)
v3 <- LoadIndexed(v2, index);

For this I introduce two new representations in the IL:

 kUntagged (for values that hold a untagged pointer) and
 
 kNoRepresentation (for instructions accept any input
 representation)

Deoptimization does not need to know about kUntagged
since these values can never occur in the environment.

Also with this change:
* fix COMPILE_ASSERT and use it in one place.
* Cleanup IL printer output of deopt ids.
Review URL: https://codereview.chromium.org//12871010

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@20198 260f80e4-7a28-3924-810f-c04153c831b5
2013-03-19 12:06:23 +00:00
fschneider@google.com d0959080ab Inline ByteArray setters like setUint8 in the optimizer.
Review URL: https://codereview.chromium.org//12378039

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@19781 260f80e4-7a28-3924-810f-c04153c831b5
2013-03-11 12:16:54 +00:00
kmillikin@google.com ef0580c26a Implement a branch optimization pass.
Branch optimization pushes some branches that test the value of a phi
to the predecessor blocks.  This can avoid materializing a boolean
object solely for the purposes of branching on its boolean value.

The optimization is performed after inlinining which creates
opportunities, and before constant propagation, because it exposes
opportunities for unreachable code elimination.

R=vegorov@google.com
BUG=

Review URL: https://codereview.chromium.org//12540002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@19682 260f80e4-7a28-3924-810f-c04153c831b5
2013-03-08 11:14:08 +00:00
kmillikin@google.com 45a6441346 Add functions for setting an environment and rebinding a use.
Add functions for setting or clearing an instruction's environment, which
initialize the environment uses.  Add a function for changing a use's
definition.

R=vegorov@google.com

Review URL: https://codereview.chromium.org//12335063

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@19036 260f80e4-7a28-3924-810f-c04153c831b5
2013-02-26 11:50:28 +00:00
lrn@google.com 3c0ac360e7 Remove deprecated string features.
Make String.codeUnits return a List.

Review URL: https://codereview.chromium.org//12282038

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@18960 260f80e4-7a28-3924-810f-c04153c831b5
2013-02-25 10:48:09 +00:00
srdjan@google.com 19995faa3a Recognize pattern (a << b) & c with c being a positive Smi and allow left shift to truncate the result.
Review URL: https://codereview.chromium.org//12218181

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@18859 260f80e4-7a28-3924-810f-c04153c831b5
2013-02-21 22:24:42 +00:00
kmillikin@google.com c3e1db1af7 Fix broken use lists in branch instructions.
BranchInstr::ReplaceWith is used in two different places that have different
expectations about the use lists of their argument.  Split it into two
separate functions.

R=fschneider@google.com
BUG=dart:8657

Review URL: https://codereview.chromium.org//12310040

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@18826 260f80e4-7a28-3924-810f-c04153c831b5
2013-02-21 12:51:01 +00:00
fschneider@google.com 8fa3140676 Inline ByteArray._setIndexed in the flow graph optimizer.
Review URL: https://codereview.chromium.org//12317011

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@18818 260f80e4-7a28-3924-810f-c04153c831b5
2013-02-21 11:35:19 +00:00
kmillikin@google.com 622efda5fb Convert some compiler passes to preserve valid def-use chains.
Change the ApplyICData, ApplyClassIds, Canonicalize, and
SelectRepresentations passes to preserve valid use lists.

Review URL: https://codereview.chromium.org//12212093

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@18676 260f80e4-7a28-3924-810f-c04153c831b5
2013-02-19 12:09:01 +00:00
vegorov@google.com baa0347253 Reapply r18377 it was reverted due to the unrelated bug it surfaced.
Remove SminessPropagator and FlowGraphTypePropagator and all associated infrastructure and fields.

Replace multiple fields (result_cid_, propagated_cid_, propagated_type_, reaching_cid_) with a single field of type CompileType which represents an element of type analysis lattice and incorporates information about: value's nullability, concrete class id and abstract super type. This ensures that propagated cid and type are always in sync and complement each other

Implement a new FlowGraphPropagator that propagates types over the CompileType-lattice.

R=fschneider@google.com

Review URL: https://codereview.chromium.org//12260008

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@18456 260f80e4-7a28-3924-810f-c04153c831b5
2013-02-13 17:16:35 +00:00
vegorov@google.com 487c73e01f Revert "Remove SminessPropagator and FlowGraphTypePropagator and all associated infrastructure and fields."
This reverts commit r12365.

Reason: failure on vm-mac-debug (debug_ia32 standalone/io/file_fuzz_test).

TBR=fschneider@google.com

Review URL: https://codereview.chromium.org//12221139

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@18378 260f80e4-7a28-3924-810f-c04153c831b5
2013-02-12 12:36:21 +00:00
vegorov@google.com f8d9a90b2c Remove SminessPropagator and FlowGraphTypePropagator and all associated infrastructure and fields.
Replace multiple fields (result_cid_, propagated_cid_, propagated_type_, reaching_cid_) with a single field of type CompileType which represents an element of type analysis lattice and incorporates information about: value's nullability, concrete class id and abstract super type. This ensures that propagated cid and type are always in sync and complement each other

Implement a new FlowGraphPropagator that propagates types over the CompileType-lattice.

BUG=

Review URL: https://codereview.chromium.org//12221119

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@18377 260f80e4-7a28-3924-810f-c04153c831b5
2013-02-12 12:06:47 +00:00
fschneider@google.com 7fc8f72c25 Inline getters of byte array view in the optimized flow graph.
This CL provides inline IL code for the getters _getInt8, _getInt16, etc.
to speed up [] and byte array views.

The code uses the existing LoadIndexed instructions by passing a index
scale factor explicitly: For normal arrays loads, the scale factor is equal
to the element size. For byte array access, the scale factor is always 1.

I'm adding inlined setters in a separate CL.
Review URL: https://codereview.chromium.org//12218008

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@18173 260f80e4-7a28-3924-810f-c04153c831b5
2013-02-06 15:18:57 +00:00
kmillikin@google.com a518a0a36f Add a use list iterator that allows mutation of current.
Add Value::Iterator that supports removing the current use from the
underlying use list, including deleting it or moving it to another use
list.  Use it in range analysis and representation selection.

R=fschneider@google.com

Review URL: https://codereview.chromium.org//12178019

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@18055 260f80e4-7a28-3924-810f-c04153c831b5
2013-02-04 17:04:02 +00:00
vegorov@google.com 932a05420a Reland r17365.
Introduce InvokeMathCFunction that can be used to directly invoke mathematical
function provided by runtime.

Use it to unconditionally inline _Double.pow.

Use it to inline floor, ceil, round, truncate, round when SSE4.1 is not
available.

Perform representation selection phase after constant propagation to minimize
boxing.

Add support for enter instruction in the x64 disassembler.

Add test for optimized pow and fix compilation on windows.

R=fschneider@google.com
BUG=dart:8002

Review URL: https://codereview.chromium.org//12038013

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@17393 260f80e4-7a28-3924-810f-c04153c831b5
2013-01-22 12:18:31 +00:00
vegorov@google.com ab91977173 Revert "Introduce InvokeMathCFunction that can be used to directly invoke mathematical function provided by runtime."
This reverts commit r17365.

TBR=fschneider@google.com

Review URL: https://codereview.chromium.org//12042014

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@17367 260f80e4-7a28-3924-810f-c04153c831b5
2013-01-21 17:16:16 +00:00
vegorov@google.com a20c8d28b8 Introduce InvokeMathCFunction that can be used to directly invoke mathematical function provided by runtime.
Use it to unconditionally inline _Double.pow.

Use it to inline floor, ceil, round, truncate, round when SSE4.1 is not available.

Perform representation selection phase after constant propagation to minimize boxing.

Add support for enter instruction in the x64 disassembler.

R=fschneider@google.com
BUG=dart:8002

Review URL: https://codereview.chromium.org//12050002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@17365 260f80e4-7a28-3924-810f-c04153c831b5
2013-01-21 16:59:37 +00:00
fschneider@google.com 657c4944c3 Remove StringCharCodeAtInstr and handle it as part of LoadIndexed.
Review URL: https://codereview.chromium.org//11970038

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@17274 260f80e4-7a28-3924-810f-c04153c831b5
2013-01-18 14:03:40 +00:00
vegorov@google.com a77fc9701c When requested to extract a method M from class C inject a method extractor (consisting of a single AST node CreateClosure) as a getter get:M into C.
This allows to cache and optimize method extraction requests as normal method invocations and at hot method extraction sites that significantly decreases overhead of method extraction which previously required two trips into runtime system and was not cached at all.

BUG=

Review URL: https://codereview.chromium.org//11642003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@17261 260f80e4-7a28-3924-810f-c04153c831b5
2013-01-18 11:54:45 +00:00
vegorov@google.com d11d988998 Set statically known ResultCid for AllocateObject.
Specialize PolymorphicInstanceCall in ApplyClassIds if receiver cid
was infered: filter out all but one target for attached ICData and drop
checks.

Canonicalize away CheckClass if reciever cid matches at least one in the list of checked.

R=fschneider@google.com
BUG=

Review URL: https://codereview.chromium.org//11886044

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@17079 260f80e4-7a28-3924-810f-c04153c831b5
2013-01-15 15:51:24 +00:00
fschneider@google.com 15432b2fee Add canonicalize optimization for branches.
Comparisons where the result is only used in a branch on true
can be folded into the branch instruction.

Patterns like this can occur after inlining and constant propagation.
In normal code, we merge branches and comparisons already at graph
building time.

v3 <- (v1 == v2)
Branch if (v3 === true)

is optimized to

Branch if (v1 == v2)

Also: Remove outdated TODOs and rename the canonicalization pass to a 
better name.
Review URL: https://codereview.chromium.org//11819031

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@16919 260f80e4-7a28-3924-810f-c04153c831b5
2013-01-10 13:18:31 +00:00
srdjan@google.com 5915aff811 Optimize instanceof: if all results are true and tests can be done using class only replace instanceof with a Boolean constant.
Review URL: https://codereview.chromium.org//11746024

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@16648 260f80e4-7a28-3924-810f-c04153c831b5
2013-01-04 21:29:05 +00:00
srdjan@google.com 29e06db609 In unoptimized code use call for instanceof instead of inlined checks. This allows us to collect type feedback and to reduce the code size of unoptimized code. Next will be work on type tests as well.
Review URL: https://codereview.chromium.org//11694003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@16589 260f80e4-7a28-3924-810f-c04153c831b5
2013-01-02 22:22:39 +00:00
asiva@google.com 7ea520f10f Create read only handles for empty_array and sentinel objects
(trying out a basic framework and will extend it to others once this
works).
Review URL: https://codereview.chromium.org//11648006

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@16416 260f80e4-7a28-3924-810f-c04153c831b5
2012-12-21 02:33:05 +00:00
vegorov@google.com 9a45691c76 When replacing one value with another ensure that replacement has SSA index assigned.
R=srdjan@google.com
BUG=dart:7513

Review URL: https://codereview.chromium.org//11638030

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@16352 260f80e4-7a28-3924-810f-c04153c831b5
2012-12-20 00:16:42 +00:00
fschneider@google.com 3a38233a6f Inline ByteArrayBase.length in the flow graph optimizer.
Review URL: https://codereview.chromium.org//11628011

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@16311 260f80e4-7a28-3924-810f-c04153c831b5
2012-12-19 10:43:13 +00:00
srdjan@google.com 85cf9af6ab Fix for issue 6678: Result of identical(a, b) with a and b doubles not consistent.
Implement proposed new identity spec (flag --new_identity_spec). It will be enabled/committed once the new spec been confirmed.

The new spec says that identity of numbers is computed on their values instead of on the object reference. This provides deterministic behavior without having to disable optimizations in the VM. In some cases 'identical' is now slower than 'equality' as more checks need to be done. The VM compiler can optimize 'identical' in the future.

My benchmarks do not show any slow down.
Review URL: https://codereview.chromium.org//11414136

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@15332 260f80e4-7a28-3924-810f-c04153c831b5
2012-11-26 18:35:45 +00:00
fschneider@google.com 2693c71850 Inline [] operator on one-byte strings.
str[i] is translated into

temp = str.charCodeAt(i)
result = StringFromCharCode(temp);

The existing code for charCodeAt is reused and contains
the necessary range class id and range check.
Review URL: https://codereview.chromium.org//11416129

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@15246 260f80e4-7a28-3924-810f-c04153c831b5
2012-11-22 12:06:52 +00:00
srdjan@google.com 251169951b Do not recompute unary_checks repeatedly. Add special (and quicker) way to check for method overrides using CHA.
Review URL: https://codereview.chromium.org//11275110

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@14434 260f80e4-7a28-3924-810f-c04153c831b5
2012-11-01 21:06:36 +00:00
vegorov@google.com 55c9c6c444 Allow bound check elimination to eliminate checks when both array length and index boundaries are expressed through the same symbol.
For example:

var list = new List(n);
for (var i = 0; i < n; i++) list[i];

R=fschneider@google.com
BUG=

Review URL: https://codereview.chromium.org//11273111

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@14293 260f80e4-7a28-3924-810f-c04153c831b5
2012-10-30 16:26:46 +00:00
vegorov@google.com 06dded663f Simple array bounds check elimination on top of range analysis framework.
Currenly eliminates only bounds checks when there is an implicit constraint bounding index's range with array length.

Does not eliminate redundancy in expressions like a[i + 1], a[i].

R=fschneider@google.com
BUG=

Review URL: https://codereview.chromium.org//11262033

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@14141 260f80e4-7a28-3924-810f-c04153c831b5
2012-10-26 16:04:55 +00:00
floitsch@google.com 09f6d09d88 Make isEmpty a getter.
Review URL: https://codereview.chromium.org//11238035

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@14022 260f80e4-7a28-3924-810f-c04153c831b5
2012-10-24 15:04:32 +00:00
fschneider@google.com 89cab1577b Enable redundancy elimination for array loads.
This CL also adds a second round of CSE if necessary to make use
 of secondary effects for more optimization opportunities.
Review URL: https://codereview.chromium.org//11234002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@13859 260f80e4-7a28-3924-810f-c04153c831b5
2012-10-22 10:40:19 +00:00
srdjan@google.com 03a61f332c Apply optimization after class-id propagation: instance calls without ICData are optimized by using input argument class-ids to create fake ICData. This reduces the number of deoptimizations.
Review URL: https://codereview.chromium.org//11187046

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@13798 260f80e4-7a28-3924-810f-c04153c831b5
2012-10-18 20:41:58 +00:00
srdjan@google.com fc6afec8de Inline indexed load and store of typed array float64.
NavierStokes time improves from 34,775us to 12,000us (v8 runs NavierStokes in 16000 us).
Review URL: https://codereview.chromium.org//11092090

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@13682 260f80e4-7a28-3924-810f-c04153c831b5
2012-10-16 15:40:54 +00:00
fschneider@google.com 54ea76dc6b Remove support for optimized dart leaf functions.
This optimization does not bring any benefit since all functions
have at least a call in the slow-path of the stack-overflow check.

I'm suggesting to remove support for this optimization since it
does not get triggered currently, therefore is also not tested.
Plus we have inlining now, which already makes calls to (small 
enough) leaf functions fast.
Review URL: https://codereview.chromium.org//11086044

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@13555 260f80e4-7a28-3924-810f-c04153c831b5
2012-10-11 16:35:47 +00:00
fschneider@google.com 5f2bdb2f7d Fix bug with missing unboxed mint-to-double conversion.
In case of a mixed integer/double operation that has a mint
input, the corresponding conversion from unboxed mint to unboxed
double was missing.

This CL converts a unboxed mint to a double by first boxing,
and then unboxing. Currently, we deoptimize in case the result
does not fit into a smi because we can only optimize mixed
smi/double operations and not yet mint/double operations.

BUG=dart:5721
TEST=tests/language/mint_arithmetic.dart
Review URL: https://codereview.chromium.org//11017017

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@13372 260f80e4-7a28-3924-810f-c04153c831b5
2012-10-08 20:20:53 +00:00
srdjan@google.com a5e9100c46 Inline String isEmpty, refactor inlining of intrinsics.
Review URL: https://codereview.chromium.org//10993023

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@13032 260f80e4-7a28-3924-810f-c04153c831b5
2012-09-28 17:40:29 +00:00
vegorov@google.com 17907d32de Implement range analysis for smi values.
And use it to eliminate overflow checks on + and - operations.

Review URL: https://codereview.chromium.org//10960014

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@12733 260f80e4-7a28-3924-810f-c04153c831b5
2012-09-21 20:06:31 +00:00
vegorov@google.com adf926862d Turn definitions that do not produce results (e.g. Checks) into instructions.
This allows more uniform iteration of IR for example when we are looking for all Smi values.

R=fschneider@google.com
BUG=

Review URL: https://codereview.chromium.org//10949019

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@12563 260f80e4-7a28-3924-810f-c04153c831b5
2012-09-19 14:38:31 +00:00
kmillikin@google.com be0492a8a8 Reapply "Initial implementation of sparse conditional constant propagation."
With a fix for compilation on Mac.  GrowableArray is DISALLOW_COPY_AND_ASSIGN,
so we can't create a temporary one to be ignored and have to pass one in to be
ignored.

R=fschneider@google.com,zerny@google.com
BUG=

Review URL: https://codereview.chromium.org//10949020

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@12561 260f80e4-7a28-3924-810f-c04153c831b5
2012-09-19 14:10:14 +00:00