InlineByteArrayBaseStore generates CheckSmi operations for certain write sizes

[mraleph]

This completely destroys performance in the AOT mode if compiler can't prove that operand is in fact a Smi.

Furthermore this is completely unnecessary because our unboxing should be able to handle both Smi and Mint cases.

Example:

import 'dart:typed_data';

const SIZE = 10 * 1024 * 1024;

@pragma('vm:never-inline')
void ok() {
  final buffer = ByteData(SIZE);
  int value = 0;
  for (var i = 0; i < buffer.lengthInBytes; i += 8) {
    buffer.setInt8(i, value++ & 0xFF);
  }
}

@pragma('vm:never-inline')
void fail() {
  final buffer = ByteData(SIZE);
  int value = 0;
  for (var i = 0; i < buffer.lengthInBytes; i += 8) {
    buffer.setInt8(i, value++);
  }
}

void measure(String name, void Function() cb) {
  final sw = Stopwatch()..start();
  cb();
  print('$name took ${sw.elapsedMilliseconds} ms.');
}


void main() {
  measure('value is known to be smi', ok);
  measure('value is not known to be smi', fail);
}

$ pkg/vm/tool/precompiler2 benchmark.dart benchmark.snap
$ out/ReleaseX64/dart_precompiled_runtime /tmp/bench.snap
value is known to be smi took 9 ms.
value is not known to be smi took 127 ms.

/cc @mkustermann

[mkustermann]

@sjindel-google Can you look at this?