[9] RFR(S): 8075136: Unnecessary sign extension for byte array access (original) (raw)

Vladimir Kozlov vladimir.kozlov at oracle.com
Fri Mar 13 18:03:34 UTC 2015

Looks good. What about other platforms? I see the same optimization in aarch64.ad

Thanks, Vladimir

On 3/13/15 7:15 AM, Tobias Hartmann wrote:

Hi,

please review the following patch. https://bugs.openjdk.java.net/browse/JDK-8075136 http://cr.openjdk.java.net/~thartmann/8075136/webrev.00/ Problem: C2 adds an unnecessary 'movslq' sign extension while compiling a byte array access: public static byte accessByte(int index) { return byteArr[index]; } 0x00007f76f4747208: movslq %esi,%r11 0x00007f76f474720b: movsbl 0x10(%r10,%r11,1),%eax Where the 'movslq' is not necessary because we emit range checks guaranteeing that index %esi is not negative. For a char array access no such sign extension is created: public static char accessChar(int index) { return charArr[index]; } 0x00007fab3916b188: movzwl 0x10(%r10,%rsi,2),%eax This is because we only have matching rules to fold the corresponding ConvI2LNode in the following case: match(AddP (AddP (DecodeN reg) (LShiftL (ConvI2L idx) scale)) off); This applies to charAccess [1] but not to byteAccess [2] because the byte array access does not require a scaling factor. Solution: I added the corresponding matching rule to fold the ConvI2LNode. match(AddP (AddP (DecodeN reg) (ConvI2L idx)) off); Testing: - Testcase - JPRT Thanks, Tobias [1] https://bugs.openjdk.java.net/secure/attachment/26108/accessChar.png [2] https://bugs.openjdk.java.net/secure/attachment/26107/accessByte.png

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