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5 Re-entrant usage of GNU lightning

GNU lightning uses the special _jit identifier. To be able to be able to use multiple jit generation states at the same time, it is required to used code similar to:

    struct jit_state lightning;
    #define lightning _jit

This will cause the symbol defined to _jit to be passed as the first argument to the underlying GNU lightning implementation, that is usually a function with an _ (underscode) prefix and with an argument named _jit, in the pattern:

    static void _jit_mnemonic(jit_state_t *, jit_gpr_t, jit_gpr_t);
    #define jit_mnemonic(u, v) _jit_mnemonic(_jit, u, v);

The reason for this is to use the same syntax as the initial lightning implementation and to avoid needing the user to keep adding an extra argument to every call, as multiple jit states generating code in paralell should be very uncommon.

5.1 Registers

6 Accessing the whole register file

As mentioned earlier in this chapter, all GNU lightning back-ends are guaranteed to have at least six general-purpose integer registers and six floating-point registers, but many back-ends will have more.

To access the entire register files, you can use the JIT_R, JIT_V and JIT_F macros. They accept a parameter that identifies the register number, which must be strictly less than JIT_R_NUM, JIT_V_NUM and JIT_F_NUM respectively; the number need not be constant. Of course, expressions like JIT_R0 and JIT_R(0) denote the same register, and likewise for integer callee-saved, or floating-point, registers.