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Re: I give up.
Jonathan Wilson writes:
> > Such as... (yesterday) gen_rtx_REG? That's in emit-rtl.c. As for
> > gen_rtx_UNSPEC, I don't know. Bear in mind that there are about a dozen
> > or so C files that are *generated* during the build. Sometimes what
> > you're looking for is in there instead, or in the generator program.
> I did finally find all the bits of code (for example in genrtl.c).
> But all that has done is made me even more confused as to just WTF all
> these functions are actually for.
> What I am looking for is a "guide to emitting RTL in GCC on i?86
> processors". Or if such a thing doesnt exist, someone out there who knows
> how to do what it is that I am trying to do and can tell me.
> Because after staring at the code, the docs, the (in this case) usless
> google search results and the back-postings to this list, I am still no
> closer to figuring out how functions like gen_rtx_UNSPEC, gen_rtx_CONST,
> gen_reg_rtx, gen_subsi3, emit_insn, gen_rtx_SET and so on actually transfer
> to the x86 assembler instructions that appear in the output thats fed to
> GAS :'(
Look at i386.c. There's a ton of examples there, such as this one in
rtx tmp, sa = EH_RETURN_STACKADJ_RTX;
tmp = gen_rtx_PLUS (Pmode, hard_frame_pointer_rtx, sa);
tmp = plus_constant (tmp, UNITS_PER_WORD);
emit_insn (gen_rtx_SET (VOIDmode, sa, tmp));
tmp = gen_rtx_MEM (Pmode, hard_frame_pointer_rtx);
emit_move_insn (hard_frame_pointer_rtx, tmp);
(stack_pointer_rtx, sa, const0_rtx));
tmp = gen_rtx_PLUS (Pmode, stack_pointer_rtx, sa);
tmp = plus_constant (tmp, (frame.to_allocate
+ frame.nregs * UNITS_PER_WORD));
emit_insn (gen_rtx_SET (VOIDmode, stack_pointer_rtx, tmp));
which generates code to adjust registers, read and write memory, and
so on. emit_insn() pushes an insn into the insn stream, which is then
optimized and converted to assembler.
Segment registers are a bit tricky.
> Normally, the usual response to "the docs, google and list archives" didnt
> help (when it comes to open source projects) is "go read the code".
> However in this case, what is one supposed to do when you have already read
> the code and even that didnt help?
That's still true.