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Fix MMIX breakage; ICE in df_ref_record, at df-scan.c:2598

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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.
This commit is contained in:
Hans-Peter Nilsson 2021-07-17 13:19:08 +02:00
parent 591b128e93
commit ef22e9c725
1 changed files with 10 additions and 3 deletions
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13
gcc/config/mmix/mmix.c
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@ -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)