Optimize _looksLikeClassName() in AOT builds. (#835)
* Optimize _looksLikeClassName() in AOT builds.
The AOT compiler does not currently compile regexes to machine code,
which makes them significantly slower. The regex in this function is
perf critical and makes the dart_style benchmark 65% slower on AOT than
on the JIT.
This fixes some of that regression.
Before:
// JIT
Best : 4.93ms ========================
Best : 4.83ms ========================
Best : 4.80ms ========================
// AOT
Best : 8.33ms =========================================
Best : 8.43ms ==========================================
Best : 8.37ms =========================================
After:
// JIT
Best : 4.93ms ========================
Best : 4.83ms ========================
Best : 4.80ms ========================
// AOT
Best : 6.93ms ==================================
Best : 6.87ms ==================================
Best : 6.77ms =================================
* Don't crash if identifier is "_".
diff --git a/lib/src/source_visitor.dart b/lib/src/source_visitor.dart
index ffef68d..fb2f231 100644
--- a/lib/src/source_visitor.dart
+++ b/lib/src/source_visitor.dart
@@ -23,8 +23,6 @@
import 'style_fix.dart';
import 'whitespace.dart';
-final _capitalPattern = RegExp(r"^_?[A-Z].*[a-z]");
-
/// Visits every token of the AST and passes all of the relevant bits to a
/// [ChunkBuilder].
class SourceVisitor extends ThrowingAstVisitor {
@@ -76,6 +74,10 @@
return target is SimpleIdentifier && _looksLikeClassName(target.name);
}
+ /// Whether [name] appears to be a type name.
+ ///
+ /// Type names begin with a capital letter and contain at least one lowercase
+ /// letter (so that we can distinguish them from SCREAMING_CAPS constants).
static bool _looksLikeClassName(String name) {
// Handle the weird lowercase corelib names.
if (name == "bool") return true;
@@ -83,7 +85,35 @@
if (name == "int") return true;
if (name == "num") return true;
- return _capitalPattern.hasMatch(name);
+ // TODO(rnystrom): A simpler implementation is to test against the regex
+ // "_?[A-Z].*?[a-z]". However, that currently has much worse performance on
+ // AOT: https://github.com/dart-lang/sdk/issues/37785.
+ const underscore = 95;
+ const capitalA = 65;
+ const capitalZ = 90;
+ const lowerA = 97;
+ const lowerZ = 122;
+
+ var start = 0;
+ var firstChar = name.codeUnitAt(start++);
+
+ // It can be private.
+ if (firstChar == underscore) {
+ if (name.length == 1) return false;
+ firstChar = name.codeUnitAt(start++);
+ }
+
+ // It must start with a capital letter.
+ if (firstChar < capitalA || firstChar > capitalZ) return false;
+
+ // And have at least one lowercase letter in it. Otherwise it could be a
+ // SCREAMING_CAPS constant.
+ for (var i = start; i < name.length; i++) {
+ var char = name.codeUnitAt(i);
+ if (char >= lowerA && char <= lowerZ) return true;
+ }
+
+ return false;
}
/// The builder for the block that is currently being visited.
