[lldb] Analyze enum promotion type during parsing (#115005)

The information about an enum's best promotion type is discarded after
compilation and is not present in debug info. This patch repeats the
same analysis of each enum value as in the front-end to determine the
best promotion type during DWARF info parsing.

Fixes #86989

Author: kuilpd

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

@@ -8474,29 +8474,22 @@ bool TypeSystemClang::CompleteTagDeclarationDefinition(
   if (enum_decl->isCompleteDefinition())
     return true;
 
-  clang::ASTContext &ast = lldb_ast->getASTContext();
-
-  /// TODO This really needs to be fixed.
-
   QualType integer_type(enum_decl->getIntegerType());
   if (!integer_type.isNull()) {
-    unsigned NumPositiveBits = 1;
+    clang::ASTContext &ast = lldb_ast->getASTContext();
+
     unsigned NumNegativeBits = 0;
+    unsigned NumPositiveBits = 0;
+    ast.computeEnumBits(enum_decl->enumerators(), NumNegativeBits,
+                        NumPositiveBits);
 
-    clang::QualType promotion_qual_type;
-    // If the enum integer type is less than an integer in bit width,
-    // then we must promote it to an integer size.
-    if (ast.getTypeSize(enum_decl->getIntegerType()) <
-        ast.getTypeSize(ast.IntTy)) {
-      if (enum_decl->getIntegerType()->isSignedIntegerType())
-        promotion_qual_type = ast.IntTy;
-      else
-        promotion_qual_type = ast.UnsignedIntTy;
-    } else
-      promotion_qual_type = enum_decl->getIntegerType();
+    clang::QualType BestPromotionType;
+    clang::QualType BestType;
+    ast.computeBestEnumTypes(/*IsPacked=*/false, NumNegativeBits,
+                             NumPositiveBits, BestType, BestPromotionType);
 
     enum_decl->completeDefinition(enum_decl->getIntegerType(),
-                                  promotion_qual_type, NumPositiveBits,
+                                  BestPromotionType, NumPositiveBits,
                                   NumNegativeBits);
   }
   return true;

lldb/test/API/lang/cpp/enum_promotion/Makefile

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

lldb/test/API/lang/cpp/enum_promotion/TestCPPEnumPromotion.py

@@ -0,0 +1,36 @@
+"""
+Test LLDB type promotion of unscoped enums.
+"""
+
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class TestCPPEnumPromotion(TestBase):
+    def test(self):
+        self.build()
+        lldbutil.run_to_source_breakpoint(
+            self, "// break here", lldb.SBFileSpec("main.cpp")
+        )
+        UChar_promoted = self.frame().FindVariable("UChar_promoted")
+        UShort_promoted = self.frame().FindVariable("UShort_promoted")
+        UInt_promoted = self.frame().FindVariable("UInt_promoted")
+        SLong_promoted = self.frame().FindVariable("SLong_promoted")
+        ULong_promoted = self.frame().FindVariable("ULong_promoted")
+        NChar_promoted = self.frame().FindVariable("NChar_promoted")
+        NShort_promoted = self.frame().FindVariable("NShort_promoted")
+        NInt_promoted = self.frame().FindVariable("NInt_promoted")
+        NLong_promoted = self.frame().FindVariable("NLong_promoted")
+
+        # Check that LLDB's promoted type is the same as the compiler's
+        self.expect_expr("+EnumUChar::UChar", result_type=UChar_promoted.type.name)
+        self.expect_expr("+EnumUShort::UShort", result_type=UShort_promoted.type.name)
+        self.expect_expr("+EnumUInt::UInt", result_type=UInt_promoted.type.name)
+        self.expect_expr("+EnumSLong::SLong", result_type=SLong_promoted.type.name)
+        self.expect_expr("+EnumULong::ULong", result_type=ULong_promoted.type.name)
+        self.expect_expr("+EnumNChar::NChar", result_type=NChar_promoted.type.name)
+        self.expect_expr("+EnumNShort::NShort", result_type=NShort_promoted.type.name)
+        self.expect_expr("+EnumNInt::NInt", result_type=NInt_promoted.type.name)
+        self.expect_expr("+EnumNLong::NLong", result_type=NLong_promoted.type.name)

lldb/test/API/lang/cpp/enum_promotion/main.cpp

@@ -0,0 +1,22 @@
+enum EnumUChar { UChar = 1 };
+enum EnumUShort { UShort = 0x101 };
+enum EnumUInt { UInt = 0x10001 };
+enum EnumSLong { SLong = 0x100000001 };
+enum EnumULong { ULong = 0xFFFFFFFFFFFFFFF0 };
+enum EnumNChar { NChar = -1 };
+enum EnumNShort { NShort = -0x101 };
+enum EnumNInt { NInt = -0x10001 };
+enum EnumNLong { NLong = -0x100000001 };
+
+int main() {
+  auto UChar_promoted = +EnumUChar::UChar;
+  auto UShort_promoted = +EnumUShort::UShort;
+  auto UInt_promoted = +EnumUInt::UInt;
+  auto SLong_promoted = +EnumSLong::SLong;
+  auto ULong_promoted = +EnumULong::ULong;
+  auto NChar_promoted = +EnumNChar::NChar;
+  auto NShort_promoted = +EnumNShort::NShort;
+  auto NInt_promoted = +EnumNInt::NInt;
+  auto NLong_promoted = +EnumNLong::NLong;
+  return 0; // break here
+}