ef22e9c725
This bug made me dive into some of the murkier waters of gcc, namely the source of operand 2 to the "call" pattern. It can be pretty poisonous, but is unused (either directly or later) by most targets. The target function_arg (and function_incoming_arg), can unless specially handled, cause a VOIDmode reg RTX to be generated, for the function arguments end-marker. This is then passed on by expand_call to the target "call" pattern, as operand[2] (which is wrongly documented or wrongly implemented, see comment in mmix.c) but unused by most targets that do not handle it specially, as in operand 2 not making it into the insn generated for the "call" (et al) patterns. Of course, the MMIX port stands out here: the RTX makes it into the generated RTX but is then actually unused and is just a placeholder; see mmix_print_operand 'p'. Anyway, df-scan inspects the emitted call rtx and horks on the void-mode RTX (actually: that it represents a zero-sized register range) from r12-1702. While I could replace or remove the emitted unused call insn operand, that would still leave unusable rtx to future users of function_arg actually looking for next_arg_reg. Better replace VOIDmode with DImode here; that's the "natural" mode of MMIX registers. (As a future improvement, I'll also remove the placeholder argument and replace the intended user; the print_operand output modifier 'p' modifier (as in "PUSHJ $%p2,%0") with some punctuation, perhaps '!' (as in "PUSHJ $%!,%0"). I inspected all ports, but other targets emit a special function_arg_info::end_marker cookie or just don't emit "call" operand[2] (etc) in the expanded "call" pattern. gcc: * config/mmix/mmix.c (mmix_function_arg_1): Avoid generating a VOIDmode register for e.g the function_arg_info::end_marker. |
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