TFA does not recognize List.from(l, growable: false) and l.toList(growable: false) #47509
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area-vm
Use area-vm for VM related issues, including code coverage, and the AOT and JIT backends.
type-performance
Issue relates to performance or code size
vm-aot-code-size
Related to improvements in AOT code size
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mraleph
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May 22, 2023
This change improves type flow analysis by adding conditional data
flow. Now each statement in the data flow summary can have an optional
condition. If a condition is present, then the statement is applied
only if its condition is not a 'false' constant. The condition may
become false as a result of whole-program type and constant
propagation (constant value is an optional property of a concrete
type).
Conditions in the data flow summary are populated from conditions in
the 'if' statements and conditional expressions. Conditions are
propagated down the control flow while building the summary.
For example:
if (x) { return foo(); }
bar();
Call 'foo()' is guarded by condition 'x' and 'bar()' is guarded by
condition '!x'.
Also, a bunch of unary and binary operations are added in order to
represent logical expressions, comparisons with null, 'is' tests and
conditional moves.
This change makes TFA much more sensitive to the control flow.
In order to offset increase in the compilation time due to the
additional condition and operations in the data flow summary,
the following is done:
* Types corresponding to bool constants are canonicalized; condition
checking and logical operations are performed using fast identical
checks.
* Fast identical checks are also added to union and intersection of
types.
* Added more sophisticated simplifications of Join statements.
Along with reduced analysis due to skipped data flow statements with
false conditions, these improvements result in the slightly reduced
compilation time.
AOT compilation time on large Flutter apps (only AOT step 2 / TFA):
App 1: Before: 65.448s After: 62.893s (-3.9%)
App 2: Before: 55.067s After: 52.192s (-5.2%)
AOT snapshot size of large Flutter apps (Flutter release mode, arm64):
App 1: Before: 32910316 After: 32599936 (-0.9%)
App 2: Before: 34464544 After: 34092907 (-1.0%)
Flutter gallery: -1.9%
Performance on micro-benchmark from #51630 in AOT mode:
Before: 0.405839
After: 0.172886 (2.3x faster than before, still slower than JIT)
TEST=pkg/vm/testcases/transformations/type_flow/transformer/regress_47509.dart
TEST=pkg/vm/testcases/transformations/type_flow/transformer/regress_51630.dart
Issue: #51630
Fixes #48154
Fixes #47509
Change-Id: I29baf2933972adf83fd58be5ec25be8c30665c01
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/300700
Reviewed-by: Martin Kustermann <kustermann@google.com>
Reviewed-by: Ömer Ağacan <omersa@google.com>
Reviewed-by: Slava Egorov <vegorov@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>
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When trying to create a test case where TFA would infer that something is a fixed length list I have noticed that TFA does not recognize either of these patterns as producing a fixed-length list. (even when l is a list literal).
/cc @alexmarkov
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