On 7/12/23 07:05, senthilkumar.selva...@microchip.com wrote:
Hi,
I've been spending some (spare) time trying to get LRA working
for the avr target.
Thank you for addressing this problem.
The code you changing is very sensitive and was a source of multiple PRs
in the past. But I found the change your propose logical and I think it
will not create problems. Still please be alert and revert the patch if
people reports the problem with this change.
After making a couple of changes to get
libgcc going, I'm now hitting an assert at
lra-constraints.cc:4423 for a subarch (avrtiny) that has a
couple of regclasses with no available registers.
The assert fires because in_class_p (correctly) returns
false for get_reg_class (regno) = ALL_REGS, and new_class =
NO_LD_REGS. For avrtiny, NO_LD_REGS is an empty regset, and
therefore hard_reg_set_subset_p (NO_LD_REGS, lra_no_alloc_regs)
is always true, making in_class_p return false.
in_class_p picks NO_LD_REGS as new_class because common_class =
ira_reg_class_subset[ALL_REGS][NO_REGS] evaluates as
NO_LD_REGS. This appears wrong to me - it should be NO_REGS
instead (lra-constraints.cc:4421 checks for NO_REGS).
ira.cc:setup_reg_class_relations sets up
ira_reg_class_subset (among other things), and the problem
appears to be a missing continue statement if
reg_class_contents[cl3] (in the innermost loop) is empty.
In this case, for cl1 = ALL_REGS and cl2 = NO_REGS, cl3 =
NO_LD_REGS, temp_hard_regset and temp_set2 are both empty, and
hard_reg_subset_p (<emptyset>, <anyval>) is always true, so
ira_reg_class_subset[ALL_REGS][NO_REGS] ends up being set to
cl3 = NO_LD_REGS. Adding a continue if hard_reg_set_empty_p
(temp_hard_regset)
fixes the problem for me.
Does the below patch look ok? Bootstrapping and regression
testing passed on x86_64.
OK.
