Richard, thank you for working on this issue and for as usually detailed
explanation of the problem.
On 2020-08-28 9:52 a.m., Richard Sandiford wrote:
...
The patch is quite aggressive in that it does this for all reload
pseudos in all reload instructions. I wondered about reusing the
condition for a reload move in in_class_p:
INSN_UID (curr_insn) >= new_insn_uid_start
&& curr_insn_set != NULL
&& ((OBJECT_P (SET_SRC (curr_insn_set))
&& ! CONSTANT_P (SET_SRC (curr_insn_set)))
|| (GET_CODE (SET_SRC (curr_insn_set)) == SUBREG
&& OBJECT_P (SUBREG_REG (SET_SRC (curr_insn_set)))
&& ! CONSTANT_P (SUBREG_REG (SET_SRC (curr_insn_set)))))))
but I can't really justify that on first principles. I think we
should apply the rule consistently until we have a specific reason
for doing otherwise.
I can not predict how the patch will behave and I can not say either
that less aggressive patch is better. So let us try.
OK for trunk?
Yes, thank you again.
If so, I think we should leave it on trunk for a bit
before backporting.
...
It seems reasonable.
I'm off next week, so if the patch is OK, I'll hold off applying
until I get back.
Richard
gcc/
PR rtl-optimization/96796
* lra-constraints.c (in_class_p): Add a default-false
allow_all_reload_class_changes_p parameter. Do not treat
reload moves specially when the parameter is true.
(get_reload_reg): Try to narrow the class of an existing OP_OUT
reload if we're reloading a reload pseudo in a reload instruction.
gcc/testsuite/
PR rtl-optimization/96796
* gcc.c-torture/compile/pr96796.c: New test.
