[OpenJDK 2D-Dev] [9] Review Request: 8080847 Copying of overlapping memory should be improved in java2d

[Sergey Bylokhov]

Hello.
Please review the fix forjdk9.

I found this issue during code review of another task, related to 
performance.

The sample code below will call the IsomorphicCopy method which call 
memcpy on the overlapping memory(this is the simplest example)

      BufferedImage img = new BufferedImage(100, 100, 
BufferedImage.TYPE_INT_ARGB_PRE);
      Graphics2D g = img.createGraphics();
      g.setComposite(AlphaComposite.Src);
      g.drawImage(img, 0, 0, null);
      g.dispose();

http://linux.die.net/man/3/memcpy
"The memcpy() function copies n bytes from memory area src to memory 
area dest. The memory areas must not overlap. Use memmove(3) if the 
memory areas do overlap"


I can confirm this bug using valgrind and a program above:
command:
valgrind --smc-check=all --tool=memcheck --leak-check=full -v 
./9/client/build/linux-x86_64-normal-server-fastdebug/images/jdk/bin/java -Xint 
Main

output:
==60975== Source and destination overlap in memcpy(0xe1b8b4d8, 
0xe1b8b4d8, 400)
==60975== at 0x4C2F71C: memcpy@@GLIBC_2.14 (in 
/usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==60975== by 0x1E0F504D: AnyIntIsomorphicCopy (in 
/moe/workspaces/jdk/9/client-work/build/linux-x86_64-normal-server-fastdebug/images/jdk/lib/amd64/libawt.so)
==60975== by 0x1E0F5DE8: Java_sun_java2d_loops_Blit_Blit (in 
/moe/workspaces/jdk/9/client-work/build/linux-x86_64-normal-server-fastdebug/images/jdk/lib/amd64/libawt.so)


Bug: https://bugs.openjdk.java.net/browse/JDK-8080847
Webrev can be found at: http://cr.openjdk.java.net/~serb/8080847/webrev.00

-- 
Best regards, Sergey.