On 7/29/2021 5:41 PM, Hans-Peter Nilsson wrote:
An old itch being scratched: the documentation lies; it's not "the
number of registers used as operands", unless the target makes a
special arrangement to that effect, and there's nothing in the guts of
gcc setting up or assuming those semantics.
Instead, see calls.c:expand_call, variable next_arg_reg. Or just
consider the variable name. The text is somewhat transcribed from the
head comment of emit_call_1 for parameter next_arg_reg. Most
important is to document the relation to function_arg_info::end_marker()
and the TARGET_FUNCTION_ARG hook.
The "normally" in the head comment, in "normally it is the first
arg-register beyond those used for args in this call, or 0 if all the
arg-registers are used in this call" means "by default", unless the
target tests end_marker_p and does something special, but the port is
free to return whatever it likes when it sees the end-marker.
And, I do mean "whatever it likes" because if the port doesn't
actually mention that operand in the RTX emitted for its "call" or
"call_value" patterns ("usually" define_expands), it can be any
mumbo-jumbo, such as a VOIDmode register, which seems like it happens
for some targets, or NULL, that happens for others. Returning a
VOIDmode register until recently included MMIX, where it made it into
the emitted RTL, confusing later passes, recently exposed as an ICE.
Tested by inspecting the info and generated pdf for sanity.
Ok for the doc part?
gcc:
* doc/md.texi (call): Correct information about operand 2.
* config/mmix/mmix.md ("call", "call_value"): Remove fixed FIXMEs.
OK
jeff
