From 08b99fe8ad6c7ed1fe7a9f352df5aac0b2f3a72b Mon Sep 17 00:00:00 2001
From: Senthil Kumar Selvaraj <saaadhu@gcc.gnu.org>
Date: Mon, 17 Jul 2023 20:04:36 +0530
Subject: [PATCH] ira: Skip empty regclass when setting up reg class relations
ira.cc:setup_reg_class_relations sets up ira_reg_class_subset (among
other things). If reg class cl3 has no registers, then that empty set
is always hard_reg_set_subset_p of any other set, and this makes
ira_reg_class_subset[ALL_REGS][NO_REGS] equal to such a regclass,
rather than NO_REGS.
This breaks code (lra-constraints.cc:in_class_p/curr_insn_transform,
for e.g.) which uses NO_REGS to check for an empty regclass.
Why define an empty regclass? A regclass could be conditionally empty (via
TARGET_CONDITIONAL_REGISTER_USAGE) - for the avr target, ADDW_REGS and
NO_LD_REGS are empty for the avrtiny subarch, for example.
Fix by continuing the innermost loop if the corresponding reg class is empty.
gcc/ChangeLog:
* ira.cc (setup_reg_class_relations): Continue
if regclass cl3 is hard_reg_set_empty_p.
---
gcc/ira.cc | 3 +++
1 file changed, 3 insertions(+)
diff --git a/gcc/ira.cc b/gcc/ira.cc
index 4a6fb357ba03..0b0d460689d5 100644
--- a/gcc/ira.cc
+++ b/gcc/ira.cc
@@ -1259,6 +1259,9 @@ setup_reg_class_relations (void)
for (cl3 = 0; cl3 < N_REG_CLASSES; cl3++)
{
temp_hard_regset = reg_class_contents[cl3] & ~no_unit_alloc_regs;
+ if (hard_reg_set_empty_p (temp_hard_regset))
+ continue;
+
if (hard_reg_set_subset_p (temp_hard_regset, intersection_set))
{
/* CL3 allocatable hard register set is inside of
--
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