[clang][DebugInfo] Revert to attaching DW_AT_const_value on static member declarations (#73626)

In #71780 we started emitting
definitions for all static data-members with constant initialisers, even
if they were constants (i.e., didn't have a location). We also dropped
the DW_AT_const_value from the declaration to [help resolve
inconsistencies during type merging in the
DWARFParallelLinker](#68721).
However, for static data members that do have locations, we wouldn't
emit a DW_AT_const_value on it, assuming that the consumer knows how to
read the value using the location. This broke some consumers that really
wanted to find a DW_AT_const_value. Ultimately we want to attach a
DW_AT_const_value to definitions that have a location too. But to fix
consumers broken by said change, this patch adds the constant back onto
the declaration. This is what we used to do prior to
#71780

Author: Michael137

clang/lib/CodeGen/CGDebugInfo.cpp

@@ -1680,14 +1680,26 @@ CGDebugInfo::CreateRecordStaticField(const VarDecl *Var, llvm::DIType *RecordTy,
   unsigned LineNumber = getLineNumber(Var->getLocation());
   StringRef VName = Var->getName();
 
+  // FIXME: to avoid complications with type merging we should
+  // emit the constant on the definition instead of the declaration.
+  llvm::Constant *C = nullptr;
+  if (Var->getInit()) {
+    const APValue *Value = Var->evaluateValue();
+    if (Value) {
+      if (Value->isInt())
+        C = llvm::ConstantInt::get(CGM.getLLVMContext(), Value->getInt());
+      if (Value->isFloat())
+        C = llvm::ConstantFP::get(CGM.getLLVMContext(), Value->getFloat());
+    }
+  }
+
   llvm::DINode::DIFlags Flags = getAccessFlag(Var->getAccess(), RD);
   auto Tag = CGM.getCodeGenOpts().DwarfVersion >= 5
                  ? llvm::dwarf::DW_TAG_variable
                  : llvm::dwarf::DW_TAG_member;
   auto Align = getDeclAlignIfRequired(Var, CGM.getContext());
-  llvm::DIDerivedType *GV =
-      DBuilder.createStaticMemberType(RecordTy, VName, VUnit, LineNumber, VTy,
-                                      Flags, /* Val */ nullptr, Tag, Align);
+  llvm::DIDerivedType *GV = DBuilder.createStaticMemberType(
+      RecordTy, VName, VUnit, LineNumber, VTy, Flags, C, Tag, Align);
   StaticDataMemberCache[Var->getCanonicalDecl()].reset(GV);
   StaticDataMemberDefinitionsToEmit.push_back(Var->getCanonicalDecl());
   return GV;

clang/test/CodeGenCXX/debug-info-static-inline-member.cpp

@@ -49,35 +49,35 @@ int main() {
 
 // CHECK:      ![[INT_DECL]] = !DIDerivedType(tag: DW_TAG_member, name: "cexpr_int_with_addr",
 // CHECK-SAME:                 flags: DIFlagStaticMember
-// CHECK-NOT:                  extraData:
+// CHECK-SAME:                 extraData: i32 25
 
 // CHECK:      ![[INT_DECL2:[0-9]+]] = !DIDerivedType(tag: DW_TAG_member, name: "cexpr_int2",
 // CHECK-SAME:                         flags: DIFlagStaticMember
-// CHECK-NOT:                          extraData:
+// CHECK-SAME:                         extraData: i32 26
 
 // CHECK:      ![[FLOAT_DECL:[0-9]+]] = !DIDerivedType(tag: DW_TAG_member, name: "cexpr_float",
 // CHECK-SAME:                          flags: DIFlagStaticMember
-// CHECK-NOT:                           extraData:
+// CHECK-SAME:                          extraData: float
 
 // CHECK:      ![[ENUM_DECL:[0-9]+]] = !DIDerivedType(tag: DW_TAG_member, name: "cexpr_enum",
 // CHECK-SAME:                         flags: DIFlagStaticMember
-// CHECK-NOT:                          extraData:
+// CHECK-SAME:                         extraData: i32 -1
 
 // CHECK:      ![[EMPTY_DECL:[0-9]+]] = !DIDerivedType(tag: DW_TAG_member, name: "cexpr_struct_with_addr",
 // CHECK-SAME:                          flags: DIFlagStaticMember
 // CHECK-NOT:                           extraData:
 
 // CHECK:      ![[IENUM_DECL:[0-9]+]] = !DIDerivedType(tag: DW_TAG_member, name: "inline_enum",
 // CHECK-SAME:                          flags: DIFlagStaticMember
-// CHECK-NOT:                           extraData:
+// CHECK-SAME:                          extraData: i32 -1
 
 // CHECK:      ![[EMPTY_TEMPLATED_DECL:[0-9]+]] = !DIDerivedType(tag: DW_TAG_member, name: "empty_templated",
 // CHECK-SAME:                                    flags: DIFlagStaticMember
-// CHECK-NOT:                                     extraData:
+// CHECK-SAME:                                    extraData: i32 1
 
 // CHECK:      ![[TEMPLATE_DECL:[0-9]+]] = !DIDerivedType(tag: DW_TAG_member, name: "cexpr_template",
 // CHECK-SAME:                             flags: DIFlagStaticMember
-// CHECK-NOT:                              extraData:
+// CHECK-SAME:                             extraData: i32 1
 
 // CHECK:      !DIGlobalVariableExpression(var: ![[EMPTY_VAR:[0-9]+]], expr: !DIExpression())
 // CHECK:      ![[EMPTY_VAR]] = distinct !DIGlobalVariable(name: "cexpr_struct_with_addr", linkageName:

clang/test/CodeGenCXX/debug-info-static-member.cpp

@@ -74,15 +74,15 @@ int C::a = 4;
 // CHECK-NOT:                           align:
 // CHECK-NOT:                           offset:
 // CHECK-SAME:                          flags: DIFlagStaticMember
-// CHECK-NOT:                           extraData:
+// CHECK-SAME:                          extraData: i1 true
 
 // DWARF4:     ![[CONST_B_DECL:[0-9]+]] = !DIDerivedType(tag: DW_TAG_member, name: "const_b"
 // DWARF5:     ![[CONST_B_DECL:[0-9]+]] = !DIDerivedType(tag: DW_TAG_variable, name: "const_b"
 // CHECK-NOT:                            size:
 // CHECK-NOT:                            align:
 // CHECK-NOT:                            offset:
 // CHECK-SAME:                           flags: DIFlagProtected | DIFlagStaticMember
-// CHECK-NOT:                            extraData:
+// CHECK-SAME:                           extraData: float
 
 // DWARF4: ![[DECL_C:[0-9]+]] = !DIDerivedType(tag: DW_TAG_member, name: "c"
 // DWARF5: ![[DECL_C:[0-9]+]] = !DIDerivedType(tag: DW_TAG_variable, name: "c"
@@ -97,7 +97,7 @@ int C::a = 4;
 // CHECK-NOT:                            align:
 // CHECK-NOT:                            offset:
 // CHECK-SAME:                           flags: DIFlagPublic | DIFlagStaticMember
-// CHECK-NOT:                            extraData:
+// CHECK-SAME:                           extraData: i32 18
 //
 // DWARF4: !DIDerivedType(tag: DW_TAG_member, name: "x_a"
 // DWARF5: !DIDerivedType(tag: DW_TAG_variable, name: "x_a"
@@ -154,7 +154,7 @@ struct V {
 // const_va is not emitted for MS targets.
 // NOT-MS: !DIDerivedType(tag: DW_TAG_member, name: "const_va",
 // NOT-MS-SAME:           line: [[@LINE-5]]
-// NOT-MS-NOT:            extraData:
+// NOT-MS-SAME:           extraData: i32 42
 const int V::const_va;
 
 namespace x {