[lldb] Fix printing of unsigned enum bitfields when they contain the max value (#96202)

While testing register fields I found that if you put the max value into
a bitfield with an underlying type that is an unsigned enum, lldb would
not print the enum name.

This is because the code to match values to names wasn't checking
whether the enum's type was signed, it just assumed it was.

So for example a 2 bit field with value 3 got signed extended to -1,
which didn't match the enumerator value of 3. So lldb just printed the
number instead of the name.

For a value of 1, the top bit was 0 so the sign extend became a zero
extend, and lldb did print the name of the enumerator.

I added a new test because I needed to use C++ to get typed enums. It
checks min, max and an in between value for signed and unsigned enums
applied to a bitfield.

Author: DavidSpickett

lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp

@@ -8639,8 +8639,13 @@ static bool DumpEnumValue(const clang::QualType &qual_type, Stream &s,
   const clang::EnumDecl *enum_decl = enutype->getDecl();
   assert(enum_decl);
   lldb::offset_t offset = byte_offset;
-  const uint64_t enum_svalue = data.GetMaxS64Bitfield(
-      &offset, byte_size, bitfield_bit_size, bitfield_bit_offset);
+  bool qual_type_is_signed = qual_type->isSignedIntegerOrEnumerationType();
+  const uint64_t enum_svalue =
+      qual_type_is_signed
+          ? data.GetMaxS64Bitfield(&offset, byte_size, bitfield_bit_size,
+                                   bitfield_bit_offset)
+          : data.GetMaxU64Bitfield(&offset, byte_size, bitfield_bit_size,
+                                   bitfield_bit_offset);
   bool can_be_bitfield = true;
   uint64_t covered_bits = 0;
   int num_enumerators = 0;
@@ -8652,8 +8657,11 @@ static bool DumpEnumValue(const clang::QualType &qual_type, Stream &s,
   // enumerators. Also 0 doesn't make sense when the enumerators are used as
   // flags.
   for (auto *enumerator : enum_decl->enumerators()) {
-    uint64_t val = enumerator->getInitVal().getSExtValue();
-    val = llvm::SignExtend64(val, 8*byte_size);
+    llvm::APSInt init_val = enumerator->getInitVal();
+    uint64_t val =
+        qual_type_is_signed ? init_val.getSExtValue() : init_val.getZExtValue();
+    if (qual_type_is_signed)
+      val = llvm::SignExtend64(val, 8 * byte_size);
     if (llvm::popcount(val) != 1 && (val & ~covered_bits) != 0)
       can_be_bitfield = false;
     covered_bits |= val;
@@ -8673,7 +8681,7 @@ static bool DumpEnumValue(const clang::QualType &qual_type, Stream &s,
   // No exact match, but we don't think this is a bitfield. Print the value as
   // decimal.
   if (!can_be_bitfield) {
-    if (qual_type->isSignedIntegerOrEnumerationType())
+    if (qual_type_is_signed)
       s.Printf("%" PRIi64, enum_svalue);
     else
       s.Printf("%" PRIu64, enum_uvalue);

lldb/test/API/commands/expression/bitfield_enums/Makefile

@@ -0,0 +1,3 @@
+CXX_SOURCES := main.cpp
+
+include Makefile.rules

lldb/test/API/commands/expression/bitfield_enums/TestBitfieldEnums.py

@@ -0,0 +1,31 @@
+"""
+Test that the expression parser accounts for the underlying type of bitfield
+enums when looking for matching values.
+"""
+
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class TestBitfieldEnum(TestBase):
+    def test_bitfield_enums(self):
+        self.build()
+
+        lldbutil.run_to_source_breakpoint(
+            self, "// break here", lldb.SBFileSpec("main.cpp", False)
+        )
+
+        self.expect_expr(
+            "bfs",
+            result_type="BitfieldStruct",
+            result_children=[
+                ValueCheck(name="signed_min", value="min"),
+                ValueCheck(name="signed_other", value="-1"),
+                ValueCheck(name="signed_max", value="max"),
+                ValueCheck(name="unsigned_min", value="min"),
+                ValueCheck(name="unsigned_other", value="1"),
+                ValueCheck(name="unsigned_max", value="max"),
+            ],
+        )

lldb/test/API/commands/expression/bitfield_enums/main.cpp

@@ -0,0 +1,24 @@
+enum class SignedEnum : int { min = -2, max = 1 };
+enum class UnsignedEnum : unsigned { min = 0, max = 3 };
+
+struct BitfieldStruct {
+  SignedEnum signed_min : 2;
+  SignedEnum signed_other : 2;
+  SignedEnum signed_max : 2;
+  UnsignedEnum unsigned_min : 2;
+  UnsignedEnum unsigned_other : 2;
+  UnsignedEnum unsigned_max : 2;
+};
+
+int main() {
+  BitfieldStruct bfs;
+  bfs.signed_min = SignedEnum::min;
+  bfs.signed_other = static_cast<SignedEnum>(-1);
+  bfs.signed_max = SignedEnum::max;
+
+  bfs.unsigned_min = UnsignedEnum::min;
+  bfs.unsigned_other = static_cast<UnsignedEnum>(1);
+  bfs.unsigned_max = UnsignedEnum::max;
+
+  return 0; // break here
+}