[lldb] Add a single bit constructor for RegisterFlags::Field (#69315)

This means you don't have to do RegisterField("", 0, 0), you can do
RegisterField("", 0).

Which is useful for testing and even more useful when we are writing
definitions of real registers which have 10s of single bit fields.

Author: DavidSpickett

lldb/include/lldb/Target/RegisterFlags.h

@@ -17,11 +17,17 @@ class RegisterFlags {
 public:
   class Field {
   public:
+    /// Where start is the least significant bit and end is the most
+    /// significant bit. The start bit must be <= the end bit.
     Field(std::string name, unsigned start, unsigned end)
         : m_name(std::move(name)), m_start(start), m_end(end) {
       assert(m_start <= m_end && "Start bit must be <= end bit.");
     }
 
+    /// Construct a field that occupies a single bit.
+    Field(std::string name, unsigned bit_position)
+        : m_name(std::move(name)), m_start(bit_position), m_end(bit_position) {}
+
     /// Get size of the field in bits. Will always be at least 1.
     unsigned GetSizeInBits() const { return m_end - m_start + 1; }
 

lldb/unittests/Target/RegisterFlagsTest.cpp

@@ -16,7 +16,7 @@ using namespace lldb;
 TEST(RegisterFlagsTest, Field) {
   // We assume that start <= end is always true, so that is not tested here.
 
-  RegisterFlags::Field f1("abc", 0, 0);
+  RegisterFlags::Field f1("abc", 0);
   ASSERT_EQ(f1.GetName(), "abc");
   // start == end means a 1 bit field.
   ASSERT_EQ(f1.GetSizeInBits(), (unsigned)1);
@@ -51,11 +51,15 @@ static RegisterFlags::Field make_field(unsigned start, unsigned end) {
   return RegisterFlags::Field("", start, end);
 }
 
+static RegisterFlags::Field make_field(unsigned bit) {
+  return RegisterFlags::Field("", bit);
+}
+
 TEST(RegisterFlagsTest, FieldOverlaps) {
   // Single bit fields
-  ASSERT_FALSE(make_field(0, 0).Overlaps(make_field(1, 1)));
-  ASSERT_TRUE(make_field(1, 1).Overlaps(make_field(1, 1)));
-  ASSERT_FALSE(make_field(1, 1).Overlaps(make_field(3, 3)));
+  ASSERT_FALSE(make_field(0, 0).Overlaps(make_field(1)));
+  ASSERT_TRUE(make_field(1, 1).Overlaps(make_field(1)));
+  ASSERT_FALSE(make_field(1, 1).Overlaps(make_field(3)));
 
   ASSERT_TRUE(make_field(0, 1).Overlaps(make_field(1, 2)));
   ASSERT_TRUE(make_field(1, 2).Overlaps(make_field(0, 1)));
@@ -71,13 +75,13 @@ TEST(RegisterFlagsTest, PaddingDistance) {
   // (start bit is higher) field first and that they do not overlap.
 
   // [field 1][field 2]
-  ASSERT_EQ(make_field(1, 1).PaddingDistance(make_field(0, 0)), 0ULL);
+  ASSERT_EQ(make_field(1, 1).PaddingDistance(make_field(0)), 0ULL);
   // [field 1][..][field 2]
-  ASSERT_EQ(make_field(2, 2).PaddingDistance(make_field(0, 0)), 1ULL);
+  ASSERT_EQ(make_field(2, 2).PaddingDistance(make_field(0)), 1ULL);
   // [field 1][field 1][field 2]
-  ASSERT_EQ(make_field(1, 2).PaddingDistance(make_field(0, 0)), 0ULL);
+  ASSERT_EQ(make_field(1, 2).PaddingDistance(make_field(0)), 0ULL);
   // [field 1][30 bits free][field 2]
-  ASSERT_EQ(make_field(31, 31).PaddingDistance(make_field(0, 0)), 30ULL);
+  ASSERT_EQ(make_field(31, 31).PaddingDistance(make_field(0)), 30ULL);
 }
 
 static void test_padding(const std::vector<RegisterFlags::Field> &fields,
@@ -99,18 +103,18 @@ TEST(RegisterFlagsTest, RegisterFlagsPadding) {
 
   // Needs padding in between the fields, single bit.
   test_padding({make_field(17, 31), make_field(0, 15)},
-               {make_field(17, 31), make_field(16, 16), make_field(0, 15)});
+               {make_field(17, 31), make_field(16), make_field(0, 15)});
   // Multiple bits of padding.
   test_padding({make_field(17, 31), make_field(0, 14)},
                {make_field(17, 31), make_field(15, 16), make_field(0, 14)});
 
   // Padding before first field, single bit.
-  test_padding({make_field(0, 30)}, {make_field(31, 31), make_field(0, 30)});
+  test_padding({make_field(0, 30)}, {make_field(31), make_field(0, 30)});
   // Multiple bits.
   test_padding({make_field(0, 15)}, {make_field(16, 31), make_field(0, 15)});
 
   // Padding after last field, single bit.
-  test_padding({make_field(1, 31)}, {make_field(1, 31), make_field(0, 0)});
+  test_padding({make_field(1, 31)}, {make_field(1, 31), make_field(0)});
   // Multiple bits.
   test_padding({make_field(2, 31)}, {make_field(2, 31), make_field(0, 1)});
 
@@ -132,9 +136,8 @@ TEST(RegisterFieldsTest, ReverseFieldOrder) {
   ASSERT_EQ(0x56781234ULL, (unsigned long long)rf2.ReverseFieldOrder(0x12345678));
 
   // Many small fields.
-  RegisterFlags rf3("", 4,
-                    {make_field(31, 31), make_field(30, 30), make_field(29, 29),
-                     make_field(28, 28)});
+  RegisterFlags rf3(
+      "", 4, {make_field(31), make_field(30), make_field(29), make_field(28)});
   ASSERT_EQ(0x00000005ULL, rf3.ReverseFieldOrder(0xA0000000));
 }
 
@@ -167,7 +170,7 @@ TEST(RegisterFlagsTest, AsTable) {
             pos_wider.AsTable(100));
 
   // Single bit fields don't need to show start and end, just one of them.
-  RegisterFlags single_bit("", 4, {make_field(31, 31)});
+  RegisterFlags single_bit("", 4, {make_field(31)});
   ASSERT_EQ("| 31 | 30-0 |\n"
             "|----|------|\n"
             "|    |      |",
@@ -177,7 +180,7 @@ TEST(RegisterFlagsTest, AsTable) {
   RegisterFlags many_fields("", 4,
                             {RegisterFlags::Field("cat", 28, 31),
                              RegisterFlags::Field("pigeon", 20, 23),
-                             RegisterFlags::Field("wolf", 12, 12),
+                             RegisterFlags::Field("wolf", 12),
                              RegisterFlags::Field("x", 0, 4)});
   ASSERT_EQ("| 31-28 | 27-24 | 23-20  | 19-13 |  12  | 11-5 | 4-0 |\n"
             "|-------|-------|--------|-------|------|------|-----|\n"