Alex <cirru...@uol.com.br> writes:
> I am a beginner on gcc backend. I was performing some experiments
> on .md file using a completly new backend set of files written by
> me. I end up on something I really could not understand. Regarding
> addition, I put the following code on my .md file:
>
> (define_expand "addhi3"
> [(set (match_operand:HI 0 "nonimmediate_operand" "")
> (plus:HI (match_operand 1 "general_operand" "")
> (match_operand 2 "general_operand" "")
> )
> )
> ]
> ""
> ""
> )
If you need a register, use a predicate of register_operand for one of
the operands. Or use force_reg in the define_expand body.
> Using this code, gcc gives the following error only when I use -O1
> (for -O0, -O2 it works OK!):
>
> (insn 16 14 17 0 (set (reg:HI 12)
> (plus:HI (mem/i:HI (symbol_ref:HI ("b") <var_decl 0x7fdad4a0
> b>) [0 b+0 S2 A16])
> (mem/i:HI (symbol_ref:HI ("a") [flags 0x2] <var_decl
> 0x7fdad430 a>) [0 a+0 S2 A16]))) -1 (nil)
> (nil))
>
> I understood that gcc would like to have a insn which accepts "reg
> = mem + mem", but I really can not understand why gcc works OK with
> -O2 and with -O0, but not with -O1.
gcc is a complex tool. There are any number of reasons why this might
happen. If you really want to know, -da will give you a lot of dump
files to look over.
Ian
