[PATCH 6/7] MIPS/testsuite: Verify MIPS16 branch stepping

["Maciej W. Rozycki" <macro@orcam.me.uk>]

From: Maciej W. Rozycki <macro@globalfoundries.com>

Verify that breakpoints are correctly placed via `mips16_next_pc' while 
single-stepping through MIPS16 branches.  Explicit instruction suffixes 
are used to get both regular and extended instruction forms covered, and 
`-Wa,-W' GAS option is used to quiesce warnings as the tool is keen to 
complain about the extended form where requested unnecessarily.

Approved-by: Maciej W. Rozycki <macro@orcam.me.uk>
---
 gdb/testsuite/gdb.arch/mips-allow.exp.tcl |   21 +++++++
 gdb/testsuite/gdb.arch/mips16-branch.c    |   82 ++++++++++++++++++++++++++++++
 gdb/testsuite/gdb.arch/mips16-branch.exp  |   30 ++++++++++
 3 files changed, 133 insertions(+)

gdb-mips16-next-pc-test.diff
Index: binutils-gdb/gdb/testsuite/gdb.arch/mips-allow.exp.tcl
===================================================================
--- binutils-gdb.orig/gdb/testsuite/gdb.arch/mips-allow.exp.tcl
+++ binutils-gdb/gdb/testsuite/gdb.arch/mips-allow.exp.tcl
@@ -84,3 +84,24 @@ proc allow_mips2_branch_tests {} {
 	{-Wa,-fatal-warnings -mno-mips16 -mno-micromips
 	    -minterlink-compressed}]
 }
+
+# Check for MIPS16 branch support.  These instructions may be absent,
+# such as with microMIPS compilations.  Make sure an actual BTEQZ
+# machine instruction is produced and no macro expanded.
+proc allow_mips16_branch_tests {} {
+    return [allow_target_tests "allow_mips16_branch_tests" \
+	"MIPS16 branch support" "(:?Bus error|Illegal instruction)" \
+	    {
+		int main() {
+		    asm volatile (
+			".set	push\n\t"
+			".set	noreorder\n\t"
+			".set	nomacro\n\t"
+			"bteqz	0f\n\t"
+			"0:\n\t"
+			".set	pop\n");
+		    return 0;
+		}
+	    } \
+	{-Wa,-fatal-warnings -mno-micromips -mips16 -minterlink-compressed}]
+}
Index: binutils-gdb/gdb/testsuite/gdb.arch/mips16-branch.c
===================================================================
--- /dev/null
+++ binutils-gdb/gdb/testsuite/gdb.arch/mips16-branch.c
@@ -0,0 +1,82 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright (C) 2026 Free Software Foundation, Inc.
+
+   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 usefu,
+   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/>.  */
+
+/* Test single-stepping through MIPS I branch instructions.  */
+
+int
+test_mips16_branch (void)
+{
+  /* Make 'err' available to the debugger to track the number of single
+     steps executed.  Use `volatile' to prevent the variable from being
+     optimized away.  */
+  volatile int err = -1;
+
+  int any = 0x55aa;
+  int mone = -1;
+  int zero = 0;
+  int one = 1;
+
+  asm volatile (
+	".macro	b_test op, args:vararg\n\t"
+	".ifb	\\args\n\t"
+	"\\op	0f\n\t"
+	".else\n\t"
+	"\\op	\\args, 0f\n\t"
+	".endif\n\t"
+	"nop\n"
+	"0:\n\t"
+	".endm\n\t"
+
+	".set	push\n\t"
+	".set	noreorder\n\t"
+	".globl	step_start\n\t"
+	".type	step_start, @function\n"
+	"step_start:\n\t"			/* Units: steps.  */
+	"nop\n\t"				/* NOP:       1s  */
+	"b_test	beqz.t %[zero]\n\t"		/* Taken:     1s  */
+	"b_test	beqz.e %[zero]\n\t"		/* Taken:     1s  */
+	"b_test	beqz.t %[any]\n\t"		/* Not taken: 2s  */
+	"b_test	beqz.e %[any]\n\t"		/* Not taken: 2s  */
+	"b_test	bnez.t %[zero]\n\t"		/* Not taken: 2s  */
+	"b_test	bnez.e %[zero]\n\t"		/* Not taken: 2s  */
+	"b_test	bnez.t %[any]\n\t"		/* Taken:     1s  */
+	"b_test	bnez.e %[any]\n\t"		/* Taken:     1s  */
+	"b_test	bteqz.t\n\t"			/* Taken:     1s  */
+	"b_test	bteqz.e\n\t"			/* Taken:     1s  */
+	"b_test	btnez.t\n\t"			/* Not taken: 2s  */
+	"b_test	btnez.e\n\t"			/* Not taken: 2s  */
+	"move	%[t], %[any]\n\t"		/* MOVE:      1s  */
+	"b_test	bteqz.t\n\t"			/* Not taken: 2s  */
+	"b_test	bteqz.e\n\t"			/* Not taken: 2s  */
+	"b_test	btnez.t\n\t"			/* Taken:     1s  */
+	"b_test	btnez.e\n\t"			/* Taken:     1s  */
+	"nop\n\t"				/* NOP:       1s  */
+	".globl	step_stop\n\t"			/* Total:    27s  */
+	".type	step_stop, @function\n"
+	"step_stop:\n\t"
+	".set pop\n"
+	: [t] "+t" (zero)
+	: [zero] "u" (zero), [any] "u" (any));
+
+  return err;
+}
+
+int
+main (void)
+{
+  return test_mips16_branch ();
+}
Index: binutils-gdb/gdb/testsuite/gdb.arch/mips16-branch.exp
===================================================================
--- /dev/null
+++ binutils-gdb/gdb/testsuite/gdb.arch/mips16-branch.exp
@@ -0,0 +1,30 @@
+# Copyright (C) 2026 Free Software Foundation, Inc.
+
+# 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/>.
+
+# Test single-stepping through MIPS16 branch instructions.
+
+require {istarget "mips*-*-*"}
+
+source $srcdir/$subdir/mips-allow.exp.tcl
+
+require allow_mips16_branch_tests
+
+standard_testfile
+
+set steps 27
+foreach flag {-Wa,-W -mno-micromips -mips16 -minterlink-compressed} {
+    lappend compile_flags "additional_flags=$flag"
+}
+source $srcdir/$subdir/mips-stepi.exp.tcl