arm: Fix CASE_VECTOR_SHORTEN_MODE for thumb2.

The CASE_VECTOR_SHORTEN_MODE query is missing some equals signs
which causes suboptimal codegen due to missed optimisation
opportunities. This patch also adds a test for thumb2
switch statements as none exist currently.

gcc/ChangeLog:
	PR target/115353
	* config/arm/arm.h (enum arm_auto_incmodes):
	Correct CASE_VECTOR_SHORTEN_MODE query.

gcc/testsuite/ChangeLog:

	* gcc.target/arm/thumb2-switchstatement.c: New test.

(cherry picked from commit 2963c76e8e24d4ebaf2b1b4ac4d7ca44eb0a9025)

2 files changed, 146 insertions, 2 deletions

diff --git a/gcc/config/arm/arm.h b/gcc/config/arm/arm.h
index 449e693..0cd5d73 100644
--- a/gcc/config/arm/arm.h
+++ b/gcc/config/arm/arm.h
@@ -2111,8 +2111,8 @@ enum arm_auto_incmodes
       ? (ADDR_DIFF_VEC_FLAGS (body).offset_unsigned = 0, HImode)	\
       : SImode)								\
    : (TARGET_THUMB2							\
-      ? ((min > 0 && max < 0x200) ? QImode				\
-      : (min > 0 && max <= 0x20000) ? HImode				\
+      ? ((min >= 0 && max < 0x200) ? QImode				\
+      : (min >= 0 && max < 0x20000) ? HImode				\
       : SImode)								\
    : ((min >= 0 && max < 1024)						\
       ? (ADDR_DIFF_VEC_FLAGS (body).offset_unsigned = 1, QImode)	\
diff --git a/gcc/testsuite/gcc.target/arm/thumb2-switchstatement.c b/gcc/testsuite/gcc.target/arm/thumb2-switchstatement.c
new file mode 100644
index 0000000..8badf31
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/thumb2-switchstatement.c
@@ -0,0 +1,144 @@
+/* { dg-do compile } */
+/* { dg-options "-mthumb --param case-values-threshold=1 -fno-reorder-blocks -fno-tree-dce -O2" } */
+/* { dg-require-effective-target arm_thumb2_ok } */
+/* { dg-final { check-function-bodies "**" "" "" } } */
+
+#define NOP "nop;"
+#define NOP2 NOP NOP
+#define NOP4 NOP2 NOP2
+#define NOP8 NOP4 NOP4
+#define NOP16 NOP8 NOP8
+#define NOP32 NOP16 NOP16
+#define NOP64 NOP32 NOP32
+#define NOP128 NOP64 NOP64
+#define NOP256 NOP128 NOP128
+#define NOP512 NOP256 NOP256
+#define NOP1024 NOP512 NOP512
+#define NOP2048 NOP1024 NOP1024
+#define NOP4096 NOP2048 NOP2048
+#define NOP8192 NOP4096 NOP4096
+#define NOP16384 NOP8192 NOP8192
+#define NOP32768 NOP16384 NOP16384
+#define NOP65536 NOP32768 NOP32768
+#define NOP131072 NOP65536 NOP65536
+
+enum z
+{
+  a = 1,
+  b,
+  c,
+  d,
+  e,
+  f = 7,
+};
+
+inline void QIFunction (const char* flag)
+{
+  asm volatile (NOP32);
+  return;
+}
+
+inline void HIFunction (const char* flag)
+{
+  asm volatile (NOP512);
+  return;
+}
+
+inline void SIFunction (const char* flag)
+{
+  asm volatile (NOP131072);
+  return;
+}
+
+/*
+**QImode_test:
+**	...
+**	tbb	\[pc, r[0-9]+\]
+**	...
+*/
+__attribute__ ((noinline)) __attribute__ ((noclone)) const char* QImode_test(enum z x)
+{
+  switch (x)
+    {
+      case d:
+        QIFunction("QItest");
+        return "InlineASM";
+      case f:
+        return "TEST";
+      default:
+        return "Default";
+    }
+}
+
+/* { dg-final { scan-assembler ".byte" } } */
+
+/*
+**HImode_test:
+**	...
+**	tbh	\[pc, r[0-9]+, lsl #1\]
+**	...
+*/
+__attribute__ ((noinline)) __attribute__ ((noclone)) const char* HImode_test(enum z x)
+{
+  switch (x)
+  {
+    case d:
+      HIFunction("HItest");
+      return "InlineASM";
+    case f:
+      return "TEST";
+    default:
+      return "Default";
+  }
+}
+
+/* { dg-final { scan-assembler ".2byte" } } */
+
+/*
+**SImode_test:
+**	...
+**	adr	(r[0-9]+), .L[0-9]+
+**	ldr	pc, \[\1, r[0-9]+, lsl #2\]
+**	...
+*/
+__attribute__ ((noinline)) __attribute__ ((noclone)) const char* SImode_test(enum z x)
+{
+  switch (x)
+  {
+    case d:
+      SIFunction("SItest");
+      return "InlineASM";
+    case f:
+      return "TEST";
+    default:
+      return "Default";
+  }
+}
+
+/* { dg-final { scan-assembler ".word" } } */
+
+/*
+**backwards_branch_test:
+**	...
+**	adr	(r[0-9]+), .L[0-9]+
+**	ldr	pc, \[\1, r[0-9]+, lsl #2\]
+**	...
+*/
+__attribute__ ((noinline)) __attribute__ ((noclone)) const char* backwards_branch_test(enum z x, int flag)
+{
+  if (flag == 5)
+  {
+    backwards:
+      asm volatile (NOP512);
+      return "ASM";
+  }
+  switch (x)
+  {
+    case d:
+      goto backwards;
+    case f:
+      return "TEST";
+    default:
+      return "Default";
+  }
+}
\ No newline at end of file