Why is 2 * (i * i) faster than 2 * i * i in Java?
The graal behavior is a lot more sane:    graal:
    [info] SoFlow.square_i_two   10000  avgt   10  5338.492 ± 36.624  ns/op   // 2 *\sum i * i
    [info] SoFlow.two_i_         10000  avgt   10  6421.343 ± 34.836  ns/op   // \sum 2 * i * i
    [info] SoFlow.two_square_i   10000  avgt   10  6367.139 ± 34.575  ns/op   // \sum 2 * (i * i)
    regular 1.8:
    [info] SoFlow.square_i_two   10000  avgt   10  6393.422 ± 27.679  ns/op
    [info] SoFlow.two_i_         10000  avgt   10  8870.908 ± 35.715  ns/op
    [info] SoFlow.two_square_i   10000  avgt   10  6221.205 ± 42.408  ns/op

The graal-generated assembly for the first two cases is nearly identical, featuring unrolled repetitions of sequences like    [info]   0x000000011433ec03: mov    %r8d,%ecx
    [info]   0x000000011433ec06: shl    %ecx               ;*imul {reexecute=0 rethrow=0 return_oop=0}
    [info]                                                 ; - add.SoFlow::test_two_i_@15 (line 41)
    [info]   0x000000011433ec08: imul   %r8d,%ecx          ;*imul {reexecute=0 rethrow=0 return_oop=0}
    [info]                                                 ; - add.SoFlow::test_two_i_@17 (line 41)
    [info]   0x000000011433ec0c: add    %ecx,%r9d          ;*iadd {reexecute=0 rethrow=0 return_oop=0}
    [info]                                                 ; - add.SoFlow::test_two_i_@18 (line 41)
    [info]   0x000000011433ec0f: lea    0x5(%r11),%r8d     ;*iinc {reexecute=0 rethrow=0 return_oop=0}
    [info]                                                 ; - add.SoFlow::test_two_i_@20 (line 40)


while the third case does a single shl at the end.    [info]   0x000000010e2918bb: imul   %r8d,%r8d          ;*imul {reexecute=0 rethrow=0 return_oop=0}
    [info]                                                 ; - add.SoFlow::test_square_i_two@15 (line 32)
    [info]   0x000000010e2918bf: add    %r8d,%ecx          ;*iadd {reexecute=0 rethrow=0 return_oop=0}
    [info]                                                 ; - add.SoFlow::test_square_i_two@16 (line 32)
    [info]   0x000000010e2918c2: lea    0x3(%r11),%r8d     ;*iinc {reexecute=0 rethrow=0 return_oop=0}
    [info]                                                 ; - add.SoFlow::test_square_i_two@18 (line 31)                                   

Both graal and C2 inline, but as usual the graal output is a lot more comprehensible.