Hi all, there has been some discussion about FPCs optimizer in #31444, prompting me to investigate some of my own code. Generally speaking the generated assembler is not all that bad (I like how it uses LEA for almost all integer arithmetics), but I keep seeing sections with lots of redundant MOVs.
Example, from a SHA512 implementation: CurrentHash is a field of the current class, compiled with anything above -O2, -CpCOREAVX2, -Px86_64. a:= CurrentHash[0]; b:= CurrentHash[1]; c:= CurrentHash[2]; d:= CurrentHash[3]; 0000000100074943 488b8424a0020000 mov 0x2a0(%rsp),%rax 000000010007494B 4c8b5038 mov 0x38(%rax),%r10 000000010007494F 488b8424a0020000 mov 0x2a0(%rsp),%rax 0000000100074957 4c8b5840 mov 0x40(%rax),%r11 000000010007495B 488b9424a0020000 mov 0x2a0(%rsp),%rdx 0000000100074963 488b4248 mov 0x48(%rdx),%rax 0000000100074967 488b9424a0020000 mov 0x2a0(%rsp),%rdx 000000010007496F 488b6a50 mov 0x50(%rdx),%rbp Every single one of the "mov 0x2a0(%rsp), %rxx" instructions except the first is redundant and causes another memory round-trip. At the same time, more registers are used, which probably makes other optimizations more difficult, especially when something similar happens on i386. Now, the fun part: I haven't been able to build a simple test that causes the same issue (the self-pointer already is in %rcx and not fetched from the stack each time), so I have a feeling this may be a side effect of some other part of the code. Does this sound familiar to anyone? If so, what could I do about it? Regards, Martok _______________________________________________ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel
