[10] RFR: 8176041: Optimize handling of comment lines in Properties$LineReader.readLine

[Claes Redestad]

Hi Aleksey!

On 03/01/2017 03:40 PM, Aleksey Shipilev wrote:
> On 03/01/2017 04:34 PM, Claes Redestad wrote:
>> the properties line reader has some relevance to startup, e.g.,
>> when reading the java.security file, and as more documentation
>> content has been added to this file it has been made apparent
>> that the handling of comment lines is inefficient due to treating
>> every character after a comment line marker ('#' or '!') as any
>> other character (writes it to an internal buffer etc) when a
>> fast-path consuming the rest of the line would do.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8176041
>> Webrev: http://cr.openjdk.java.net/~redestad/8176041/jdk.01
> The idea looks fine.
>
> I think you can go further and unswitch the loop, saving branch in a hot loop,
> and using byte comparisons (may require some work to do efficient byte-char
> comparisons):
>
>      if (inStream != null) {
>         while (inOff < inLimit) {
>            byte b = inByteBuf[inOff++];
>            if (b == '\n' || b == '\r' || b == '\\') {
>               break;
>            }
>         }
>      } else {
>         while (inOff < inLimit) {
>            c = inCharBuf[inOff++];
>            if (c == '\n' || c == '\r' || c == '\\') {
>               break;
>            }
>         }
>      }

Sure, with a bit of fix-up this drops another 170k executed bytecodes
to read in the java.security file (original: 1882k, now: 980k):

http://cr.openjdk.java.net/~redestad/8176041/jdk.02/

It seems javac optimizes byte-char comparisons pretty well in this
case since the chars we're comparing against are all in the 0-127 range,
so I don't think there's much we can do:

        256: getfield      #7                  // Field inByteBuf:[B
        259: aload_0
        260: dup
        261: getfield      #5                  // Field inOff:I
        264: dup_x1
        265: iconst_1
        266: iadd
        267: putfield      #5                  // Field inOff:I
        270: baload
        271: istore        9
        273: iload         9
        275: bipush        10     <- '\n'
        277: if_icmpeq     294
        280: iload         9
        282: bipush        13  <- '\r'
        284: if_icmpeq     294
        287: iload         9
        289: bipush        92   <- '\\'

Thanks!

/Claes

>
> Thanks,
> -Aleksey
>