[clang] [clang][DebugInfo] Attach DW_AT_const_value to static data-member definitions if available (PR #72730)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-debuginfo

Author: Michael Buch (Michael137)

<details>
<summary>Changes</summary>

In https://github.com/llvm/llvm-project/pull/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](https://github.com/llvm/llvm-project/pull/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`.

This patch makes sure we also attach the `DW_AT_const_value` to definitions that have a location.

---
Full diff: https://github.com/llvm/llvm-project/pull/72730.diff


3 Files Affected:

- (modified) clang/lib/CodeGen/CGDebugInfo.cpp (+22-6) 
- (modified) clang/test/CodeGenCXX/debug-info-static-inline-member.cpp (+1-1) 
- (modified) clang/test/CodeGenCXX/inline-dllexport-member.cpp (+1-1) 


``````````diff
diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
index 0b52d99ad07f164..e01c57baef19931 100644
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -69,6 +69,19 @@ static uint32_t getDeclAlignIfRequired(const Decl *D, const ASTContext &Ctx) {
   return D->hasAttr<AlignedAttr>() ? D->getMaxAlignment() : 0;
 }
 
+APValue const *evaluateConstantInitializer(clang::VarDecl const *VD) {
+  assert(VD != nullptr);
+
+  VD = VD->getCanonicalDecl();
+  if (!VD)
+    return nullptr;
+
+  if (!VD->hasConstantInitialization() || !VD->hasInit())
+    return nullptr;
+
+  return VD->evaluateValue();
+}
+
 CGDebugInfo::CGDebugInfo(CodeGenModule &CGM)
     : CGM(CGM), DebugKind(CGM.getCodeGenOpts().getDebugInfo()),
       DebugTypeExtRefs(CGM.getCodeGenOpts().DebugTypeExtRefs),
@@ -5503,11 +5516,17 @@ void CGDebugInfo::EmitGlobalVariable(llvm::GlobalVariable *Var,
     }
     AppendAddressSpaceXDeref(AddressSpace, Expr);
 
+    llvm::DIExpression *E = nullptr;
+    if (Expr.empty()) {
+      if (auto const *InitVal = evaluateConstantInitializer(D))
+        E = createConstantValueExpression(D, *InitVal);
+    } else
+      E = DBuilder.createExpression(Expr);
+
     llvm::DINodeArray Annotations = CollectBTFDeclTagAnnotations(D);
     GVE = DBuilder.createGlobalVariableExpression(
         DContext, DeclName, LinkageName, Unit, LineNo, getOrCreateType(T, Unit),
-        Var->hasLocalLinkage(), true,
-        Expr.empty() ? nullptr : DBuilder.createExpression(Expr),
+        Var->hasLocalLinkage(), true, E,
         getOrCreateStaticDataMemberDeclarationOrNull(D), TemplateParameters,
         Align, Annotations);
     Var->addDebugInfo(GVE);
@@ -5596,14 +5615,11 @@ void CGDebugInfo::EmitGlobalVariable(const VarDecl *VD) {
   if (VD->hasAttr<NoDebugAttr>())
     return;
 
-  if (!VD->hasInit())
-    return;
-
   const auto CacheIt = DeclCache.find(VD);
   if (CacheIt != DeclCache.end())
     return;
 
-  auto const *InitVal = VD->evaluateValue();
+  auto const *InitVal = evaluateConstantInitializer(VD);
   if (!InitVal)
     return;
 
diff --git a/clang/test/CodeGenCXX/debug-info-static-inline-member.cpp b/clang/test/CodeGenCXX/debug-info-static-inline-member.cpp
index f2d4d9408a8297a..950ea9b302b290c 100644
--- a/clang/test/CodeGenCXX/debug-info-static-inline-member.cpp
+++ b/clang/test/CodeGenCXX/debug-info-static-inline-member.cpp
@@ -43,7 +43,7 @@ int main() {
 // CHECK:      @{{.*}}cexpr_struct_with_addr{{.*}} = 
 // CHECK-SAME    !dbg ![[EMPTY_GLOBAL:[0-9]+]]
 
-// CHECK:      !DIGlobalVariableExpression(var: ![[INT_VAR:[0-9]+]], expr: !DIExpression())
+// CHECK:      !DIGlobalVariableExpression(var: ![[INT_VAR:[0-9]+]], expr: !DIExpression(DW_OP_constu, 25, DW_OP_stack_value))
 // CHECK:      ![[INT_VAR]] = distinct !DIGlobalVariable(name: "cexpr_int_with_addr", linkageName:
 // CHECK-SAME:                isLocal: false, isDefinition: true, declaration: ![[INT_DECL:[0-9]+]])
 
diff --git a/clang/test/CodeGenCXX/inline-dllexport-member.cpp b/clang/test/CodeGenCXX/inline-dllexport-member.cpp
index d6b004d66dc6cbd..6bc01599c466780 100644
--- a/clang/test/CodeGenCXX/inline-dllexport-member.cpp
+++ b/clang/test/CodeGenCXX/inline-dllexport-member.cpp
@@ -7,7 +7,7 @@ struct __declspec(dllexport) s {
   static const unsigned int ui = 0;
 };
 
-// CHECK: [[UI]] = !DIGlobalVariableExpression(var: [[UIV:.*]], expr: !DIExpression())
+// CHECK: [[UI]] = !DIGlobalVariableExpression(var: [[UIV:.*]], expr: !DIExpression(DW_OP_constu, 0, DW_OP_stack_value))
 // CHECK: [[UIV]] = distinct !DIGlobalVariable(name: "ui", linkageName: "?ui at s@@2IB", scope: ![[SCOPE:[0-9]+]],
 // CHECK: ![[SCOPE]] = distinct !DICompileUnit(
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/72730