dart2js Uri patch: avoid unnecessary code-unit to String conversions

dart2js Uri patch: avoid unnecessary code-unit to String conversions

results in:

H.Primitives_stringFromCharCode(C.JSString_methods.codeUnitAt$1("0123456789ABCDEF", $byte & 15)
-->
"0123456789ABCDEF"[$byte & 15]

dart2js does not know how to do this yet.

R=lrn@google.com

Committed: https://github.com/dart-lang/sdk/commit/b3a4cc337c0f90baec31e518af0dfb78b2fbf1d8

[sra1, 2015-11-05 20:22:05]

sra@google.com changed reviewers:
+ lrn@google.com

[Lasse Reichstein Nielsen, 2015-11-05 21:48:26]

lgtm

https://codereview.chromium.org/1420303011/diff/1/sdk/lib/_internal/js_runtim...
File sdk/lib/_internal/js_runtime/lib/core_patch.dart (right):

https://codereview.chromium.org/1420303011/diff/1/sdk/lib/_internal/js_runtim...
sdk/lib/_internal/js_runtime/lib/core_patch.dart:566:
result.write(hexDigits[byte & 0x0f]);
I guess it's OK, but it's a sign that dart2js' StringBuffer needs optimization
for code units.

[sra1, 2015-11-06 01:55:10]

https://codereview.chromium.org/1420303011/diff/1/sdk/lib/_internal/js_runtim...
File sdk/lib/_internal/js_runtime/lib/core_patch.dart (right):

https://codereview.chromium.org/1420303011/diff/1/sdk/lib/_internal/js_runtim...
sdk/lib/_internal/js_runtime/lib/core_patch.dart:566:
result.write(hexDigits[byte & 0x0f]);
On 2015/11/05 21:48:26, Lasse Reichstein Nielsen wrote:
> I guess it's OK, but it's a sign that dart2js' StringBuffer needs optimization
> for code units.

It is really hard to get JavaScript performance with char codes anywhere near
using strings, which have been much more heavily optimized in most
implementations.

Our StringBuffer implementation is so simple that this function now compiles to
the following.
Can you find the StringBuffer?

        Uri__uriEncode: function(canonicalTable, text, encoding, spaceToPlus) {
          var bytes, t1, i, t2, $byte, t3;
          if (encoding === C.Utf8Codec_false &&
$.$get$Uri__needsNoEncoding()._nativeRegExp.test(H.checkString(text)))
            return text;
          bytes = encoding.get$encoder().convert$1(text);
          for (t1 = bytes.length, i = 0, t2 = ""; i < t1; ++i) {
            $byte = bytes[i];
            if ($byte < 128) {
              t3 = $byte >>> 4;
              if (t3 >= 8)
                return H.ioore(canonicalTable, t3);
              t3 = (canonicalTable[t3] & C.JSInt_methods._shlPositive$1(1, $byte
& 15)) !== 0;
            } else
              t3 = false;
            if (t3)
              t2 += H.Primitives_stringFromCharCode($byte);
            else
              t2 = spaceToPlus && $byte === 32 ? t2 + "+" : t2 + "%" +
"0123456789ABCDEF"[$byte >>> 4 & 15] + "0123456789ABCDEF"[$byte & 15];
          }
          return t2.charCodeAt(0) == 0 ? t2 : t2;
        }

[sra1, 2015-11-06 01:55:59]

Committed patchset #1 (id:1) manually as
b3a4cc337c0f90baec31e518af0dfb78b2fbf1d8 (presubmit successful).