sljit

A few other small and fast JITs: https://github.com/zherczeg/sljit (used by libpcre), https://github.com/asmjit/asmjit (RPCS3 and FBGEMM) and https://webkit.org/blog/5852/introducing-the-b3-jit-compiler... (only used by JSC in Webkit, I think)

This is interesting: https://github.com/zherczeg/sljit/blob/master/sljit_src/slji... (Lines 167-205): // Scratch registers. #define SLJIT_R0 1 #define SLJIT_R1 2 #define SLJIT_R2 3 // Note: on x86-32, R3 - R6 (same as S3 - S6) are emulated (they are allocated on the stack). These registers are called virtual and cannot be used for memory addressing (cannot be part of any SLJIT_MEM1, SLJIT_MEM2 construct). There is no such limitation on other CPUs. See sljit_get_register_index(). #define SLJIT_R3 4 [...] #define SLJIT_R9 10 [...] /* Saved registers. */ #define SLJIT_S0 (SLJIT_NUMBER_OF_REGISTERS) #define SLJIT_S1 (SLJIT_NUMBER_OF_REGISTERS - 1) #define SLJIT_S2 (SLJIT_NUMBER_OF_REGISTERS - 2) // Note: on x86-32, S3 - S6 (same as R3 - R6) are emulated (they are allocated on the stack). These registers are called virtual and cannot be used f

Although I only looked at the code briefly I suspect it will very hard to get good performance from the API as provided[1]. It looks like you have to do a function call for every high level assembly instruction which in turn does quite a bit of work. See `emit_x86_instruction`[2], most of which is redundant and most of which can be done ahead of time. To JIT quickly you want to work with templates if at all possible. Precompile those templates for the relevant architecture. Then at runtime you just patch the precompiled machine code with the correct addresses and registers. This extra speed really matters because if JITing code is cheap you can compile functions multiple times, inline aggressively and do many other optimizations that wouldn't be economical otherwise. [1] https://github.com/zherczeg/sljit/blob/master/test_src/sljit... [2]:

https://zherczeg.github.io/sljit https://github.com/zherczeg/sljit Meany leany?