From ef22e9c725cc94b68c27b09503bfc4b4064d8dbf Mon Sep 17 00:00:00 2001 From: Hans-Peter Nilsson Date: Sat, 17 Jul 2021 13:19:08 +0200 Subject: [PATCH] Fix MMIX breakage; ICE in df_ref_record, at df-scan.c:2598 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. --- gcc/config/mmix/mmix.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/gcc/config/mmix/mmix.c b/gcc/config/mmix/mmix.c index 40bfb4314dd..db7af7b75b6 100644 --- a/gcc/config/mmix/mmix.c +++ b/gcc/config/mmix/mmix.c @@ -667,10 +667,17 @@ mmix_function_arg_1 (const cumulative_args_t argsp_v, { CUMULATIVE_ARGS *argsp = get_cumulative_args (argsp_v); + /* The mode of the argument will be VOIDmode for the "end_marker". Make sure + we don't ever generate a VOIDmode register; later passes will barf on that. + We may want to use the register number, so return something nominally + useful. Thus, for VOIDmode, use DImode, being the natural mode for the + register. */ + machine_mode mode = arg.mode == VOIDmode ? DImode : arg.mode; + /* Last-argument marker. */ if (arg.end_marker_p ()) return (argsp->regs < MMIX_MAX_ARGS_IN_REGS) - ? gen_rtx_REG (arg.mode, + ? gen_rtx_REG (mode, (incoming ? MMIX_FIRST_INCOMING_ARG_REGNUM : MMIX_FIRST_ARG_REGNUM) + argsp->regs) @@ -678,10 +685,10 @@ mmix_function_arg_1 (const cumulative_args_t argsp_v, return (argsp->regs < MMIX_MAX_ARGS_IN_REGS && !targetm.calls.must_pass_in_stack (arg) - && (GET_MODE_BITSIZE (arg.mode) <= 64 + && (GET_MODE_BITSIZE (mode) <= 64 || argsp->lib || TARGET_LIBFUNC)) - ? gen_rtx_REG (arg.mode, + ? gen_rtx_REG (mode, (incoming ? MMIX_FIRST_INCOMING_ARG_REGNUM : MMIX_FIRST_ARG_REGNUM)