[PATCH] sim: pru: Fix behaviour when loop count is zero

[Dimitar Dimitrov <dimitar@dinux.eu>]

If the counter for LOOP instruction is provided by a register with
value zero, then the instruction must cause a PC jump directly to the
loop end.  But in that particular case simulator must not initialize
its internal loop variables, because loop body will not be executed.
Instead, simulator must obtain the loop's end address directly from
the LOOP instruction.

Ok for trunk?

Signed-off-by: Dimitar Dimitrov <dimitar@dinux.eu>
---
 sim/pru/pru.isa               |  4 ++--
 sim/testsuite/pru/loop-zero.s | 41 +++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+), 2 deletions(-)
 create mode 100644 sim/testsuite/pru/loop-zero.s

diff --git a/sim/pru/pru.isa b/sim/pru/pru.isa
index b7d8b4af8b9..be8cdfd27fb 100644
--- a/sim/pru/pru.isa
+++ b/sim/pru/pru.isa
@@ -222,7 +222,7 @@ INSTRUCTION (loop,
 	     OP2 = (IO ? IMM8 + 1 : RS2_w0);
 	     if (OP2 == 0)
 	      {
-		PC = LOOPEND;
+		PC = PC + LOOP_JMPOFFS;
 	      }
 	     else
 	      {
@@ -237,7 +237,7 @@ INSTRUCTION (iloop,
 	     OP2 = (IO ? IMM8 + 1 : RS2_w0);
 	     if (OP2 == 0)
 	      {
-		PC = LOOPEND;
+		PC = PC + LOOP_JMPOFFS;
 	      }
 	     else
 	      {
diff --git a/sim/testsuite/pru/loop-zero.s b/sim/testsuite/pru/loop-zero.s
new file mode 100644
index 00000000000..65330f27beb
--- /dev/null
+++ b/sim/testsuite/pru/loop-zero.s
@@ -0,0 +1,41 @@
+# Check that loop insn works if register value is zero.
+# mach: pru
+
+# Copyright (C) 2022 Free Software Foundation, Inc.
+# Contributed by Dimitar Dimitrov <dimitar@dinux.eu>
+#
+# This file is part of the GNU simulators.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+.include "testutils.inc"
+
+	start
+
+	ldi r25, 0
+	ldi r27, 0
+	ldi r28, 10
+
+	loop 1f, r25
+	add r27, r27, 1
+	add r28, r28, 1
+1:
+
+	qbne F, r25, 0
+	qbne F, r27, 0
+	qbne F, r28, 10
+
+	pass
+
+F:	fail
-- 
2.38.1