RFR(M): 8073480: C2 should optimize explicit range checks

[Roland Westrelin]

> For example, here is the main loop for u_loop on jdk9/dev (using -XX:LoopUnrollLimit=0):
> 
> 0x000000010ba77938: test   %ecx,%ecx
> 0x000000010ba7793a: jl     0x000000010ba779d2  ;*iflt
>                                              ; - arrays.ArrayTest::u at 1 (line 71)
>                                              ; - arrays.ArrayTest::u_loop at 19 (line 65)
> 
> 0x000000010ba77940: cmp    %ebp,%ecx
> 0x000000010ba77942: jge    0x000000010ba779f9  ;*if_icmplt
>                                              ; - arrays.ArrayTest::u at 7 (line 71)
>                                              ; - arrays.ArrayTest::u_loop at 19 (line 65)
> 
> 0x000000010ba77948: movslq %ecx,%r10
> 0x000000010ba7794b: add    0x10(%rbx,%r10,4),%eax  ;*iadd
>                                              ; - arrays.ArrayTest::u_loop at 22 (line 65)
> 
> 0x000000010ba77950: inc    %ecx               ;*iinc
>                                              ; - arrays.ArrayTest::u_loop at 24 (line 64)
> 
> 0x000000010ba77952: cmp    %r8d,%ecx
> 0x000000010ba77955: jl     0x000000010ba77938  ;*if_icmpge
>                                              ; - arrays.ArrayTest::u_loop at 12 (line 64)
> 
> 
> And here is the same on jdk9/hs-rt with your patch applied:
> 
> 0x0000000110355f40: movslq %r10d,%r9
> 0x0000000110355f43: add    0x10(%r8,%r9,4),%eax  ;*iadd
>                                              ; - arrays.ArrayTest::u_loop at 22 (line 65)
> 
> 0x0000000110355f48: inc    %r10d              ;*iinc
>                                              ; - arrays.ArrayTest::u_loop at 24 (line 64)
> 
> 0x0000000110355f4b: cmp    %r11d,%r10d
> 0x0000000110355f4e: jl     0x0000000110355f40  ;*if_icmpge
>                                              ; - arrays.ArrayTest::u_loop at 12 (line 64)
> 
> I wish we could get rid of those pesky "movslq" instructions :-) but IIUC that is tricky.

Are the movslq there only for the u_loop() case? Can you send me your test case. I’ll see if I can make them go away.

Roland.