[Clang] Fix static const member address reference #169251

pfeodrippe · 2025-11-23T22:36:35Z

Used Copilot. Run all clang tests locally with ninja check-clang (everything that was passing in main is also passing here.)

From #146956 clang::Interpreter cannot get the address of a static const member`, we can see the issue below.

The fix, only applied in incremental mode (clang-repl / Interpreter), seems to be to ensure static data members with in-class initializers are materialized before use.

# Unable to take the address of a static const member.
❯ clang-repl
clang-repl> struct foo{ static int const bar{ 5 }; };
clang-repl> int const *p{ &foo::bar };
clang-repl> #include <cstdio>
clang-repl> printf("%d\n", *p);
JIT session error: Symbols not found: [ _ZN3foo3barE ]
Segmentation fault (core dumped)

# Getting its value works fine.
❯ clang-repl
clang-repl> struct foo{ static int const bar{ 5 }; };
clang-repl> int const i{ foo::bar };
clang-repl> #include <cstdio>
clang-repl> printf("%d\n", i);
5

# LLVM 22 (head)

github-actions · 2025-11-23T22:36:54Z

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jeaye · 2025-11-25T20:19:15Z

@vgvassilev Would you please review for viability? Paulo's trying to fix #146956, which is a bug preventing clang::Interpreter from accessing static data members by reference or address.

llvmbot · 2025-11-26T03:06:00Z

@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clang-codegen

Author: Paulo Rafael Feodrippe (pfeodrippe)

Changes

Fixes #146956

Used Copilot. Run all clang tests locally with ninja check-clang (everything that was passing in main is also passing here.)

From #146956 clang::Interpreter cannot get the address of a static const member`, we can see the issue below.

The fix seems to be to ensure static data members with in-class initializers are materialized before use.

# Unable to take the address of a static const member.
❯ clang-repl
clang-repl&gt; struct foo{ static int const bar{ 5 }; };
clang-repl&gt; int const *p{ &amp;foo::bar };
clang-repl&gt; #include &lt;cstdio&gt;
clang-repl&gt; printf("%d\n", *p);
JIT session error: Symbols not found: [ _ZN3foo3barE ]
Segmentation fault (core dumped)

# Getting its value works fine.
❯ clang-repl
clang-repl&gt; struct foo{ static int const bar{ 5 }; };
clang-repl&gt; int const i{ foo::bar };
clang-repl&gt; #include &lt;cstdio&gt;
clang-repl&gt; printf("%d\n", i);
5

# LLVM 22 (head)

Full diff: https://github.com/llvm/llvm-project/pull/169251.diff

6 Files Affected:

(modified) clang/lib/CodeGen/CGExpr.cpp (+6)
(modified) clang/lib/CodeGen/CGExprConstant.cpp (+4)
(modified) clang/lib/CodeGen/CodeGenModule.cpp (+45)
(modified) clang/lib/CodeGen/CodeGenModule.h (+8)
(added) clang/test/Interpreter/static-const-member.cpp (+59)
(modified) clang/unittests/Interpreter/InterpreterTest.cpp (+14)

diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index b33772919b8c8..9f3b7f686fe4e 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -3111,6 +3111,12 @@ static LValue EmitGlobalVarDeclLValue(CodeGenFunction &CGF,
       return CGF.MakeAddrLValue(Addr, T, AlignmentSource::Decl);
   }
 
+  // In incremental mode, ensure static data members with in-class initializers
+  // are materialized before use. This handles lvalue references that bypass
+  // constant evaluation (e.g., passing by reference to a function).
+  if (CGF.CGM.getLangOpts().IncrementalExtensions && VD->isStaticDataMember())
+    VD = CGF.CGM.materializeStaticDataMember(VD);
+
   llvm::Value *V = CGF.CGM.GetAddrOfGlobalVar(VD);
 
   if (VD->getTLSKind() != VarDecl::TLS_None)
diff --git a/clang/lib/CodeGen/CGExprConstant.cpp b/clang/lib/CodeGen/CGExprConstant.cpp
index 6407afc3d9447..2a97f509b4b9b 100644
--- a/clang/lib/CodeGen/CGExprConstant.cpp
+++ b/clang/lib/CodeGen/CGExprConstant.cpp
@@ -2243,6 +2243,10 @@ ConstantLValueEmitter::tryEmitBase(const APValue::LValueBase &base) {
     }
 
     if (const auto *VD = dyn_cast<VarDecl>(D)) {
+      // In incremental mode, ensure static data members with in-class
+      // initializers are materialized on first odr-use (e.g., &Foo::member).
+      if (CGM.getLangOpts().IncrementalExtensions && VD->isStaticDataMember())
+        VD = CGM.materializeStaticDataMember(VD);
       // We can never refer to a variable with local storage.
       if (!VD->hasLocalStorage()) {
         if (VD->isFileVarDecl() || VD->hasExternalStorage())
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 645b78a599f89..eba02c980747e 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -6302,6 +6302,51 @@ CodeGenModule::getLLVMLinkageVarDefinition(const VarDecl *VD) {
   return getLLVMLinkageForDeclarator(VD, Linkage);
 }
 
+const VarDecl *CodeGenModule::materializeStaticDataMember(const VarDecl *VD) {
+  if (!VD)
+    return VD;
+
+  const VarDecl *DefinitionVD = VD->getDefinition();
+  if (!DefinitionVD)
+    DefinitionVD = VD;
+
+  // Only in-class static data members need materialization. Out-of-line
+  // definitions are emitted normally.
+  if (!DefinitionVD->isStaticDataMember() || DefinitionVD->isOutOfLine())
+    return DefinitionVD;
+
+  const VarDecl *InitVD = nullptr;
+  // Members without in-class initializers rely on out-of-class definitions.
+  if (!DefinitionVD->getAnyInitializer(InitVD) || !InitVD)
+    return DefinitionVD;
+
+  auto NeedsMaterialization = [](llvm::GlobalValue *GV) {
+    if (!GV)
+      return true;
+    if (GV->isDeclaration())
+      return true;
+    // Inline static members may be emitted as available_externally; upgrade
+    // to linkonce_odr so the JIT can resolve them.
+    if (auto *GVVar = llvm::dyn_cast<llvm::GlobalVariable>(GV))
+      return GVVar->hasAvailableExternallyLinkage();
+    return false;
+  };
+
+  GlobalDecl GD(InitVD);
+  StringRef MangledName = getMangledName(GD);
+  llvm::GlobalValue *GV = GetGlobalValue(MangledName);
+
+  if (NeedsMaterialization(GV)) {
+    EmitGlobalVarDefinition(InitVD, /*IsTentative=*/false);
+    GV = GetGlobalValue(MangledName);
+    if (auto *GVVar = llvm::dyn_cast_or_null<llvm::GlobalVariable>(GV))
+      if (GVVar->hasAvailableExternallyLinkage())
+        GVVar->setLinkage(llvm::GlobalValue::LinkOnceODRLinkage);
+  }
+
+  return InitVD;
+}
+
 /// Replace the uses of a function that was declared with a non-proto type.
 /// We want to silently drop extra arguments from call sites
 static void replaceUsesOfNonProtoConstant(llvm::Constant *old,
diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
index a253bcda2d06c..1ea582c03a8c6 100644
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -1839,6 +1839,14 @@ class CodeGenModule : public CodeGenTypeCache {
     return TrapReasonBuilder(&getDiags(), DiagID, TR);
   }
 
+  /// Materialize a static data member with an in-class initializer on demand.
+  ///
+  /// In incremental contexts (e.g. clang-repl) a class can be defined in an
+  /// earlier partial translation unit, while the first odr-use (such as taking
+  /// the address) happens later. Ensure we emit a usable definition so the JIT
+  /// can resolve the symbol.
+  const VarDecl *materializeStaticDataMember(const VarDecl *VD);
+
 private:
   bool shouldDropDLLAttribute(const Decl *D, const llvm::GlobalValue *GV) const;
 
diff --git a/clang/test/Interpreter/static-const-member.cpp b/clang/test/Interpreter/static-const-member.cpp
new file mode 100644
index 0000000000000..3ba52679305a4
--- /dev/null
+++ b/clang/test/Interpreter/static-const-member.cpp
@@ -0,0 +1,59 @@
+// RUN: cat %s | clang-repl | FileCheck %s
+// Tests for static const member materialization in clang-repl.
+// See https://github.com/llvm/llvm-project/issues/146956
+
+extern "C" int printf(const char*, ...);
+
+struct Foo { static int const bar { 5 }; static int const baz { 10 }; };
+
+// Test 1: Taking address of static const member
+int const * p = &Foo::bar;
+printf("Address test: %d\n", *p);
+// CHECK: Address test: 5
+
+// Test 2: Multiple static const members in same class
+int const * q = &Foo::baz;
+printf("Second member test: %d\n", *q);
+// CHECK: Second member test: 10
+
+// Test 3: static constexpr member (variant of in-class init)
+struct Qux { static constexpr int val = 99; };
+int const *p3 = &Qux::val;
+printf("Constexpr test: %d\n", *p3);
+// CHECK: Constexpr test: 99
+
+// Test 4: Passing static const member by reference (exercises CGExpr.cpp path)
+// NOTE: Uses a separate struct to ensure this is the first odr-use of RefOnly::val
+struct RefOnly { static int const val { 77 }; };
+void useRef(int const &x) { printf("Ref test: %d\n", x); }
+useRef(RefOnly::val);
+// CHECK: Ref test: 77
+
+// ============================================================================
+// Negative tests - cases that should NOT trigger materialization
+// ============================================================================
+
+// Test 5: Out-of-class definition (no need to materialize - already defined)
+struct OutOfLine { static const int value; };
+const int OutOfLine::value = 23;
+int const *p5 = &OutOfLine::value;
+printf("Out-of-line test: %d\n", *p5);
+// CHECK: Out-of-line test: 23
+
+// Test 6: Non-const static member (normal code gen path)
+struct NonConst { static int value; };
+int NonConst::value = 42;
+int *p6 = &NonConst::value;
+printf("Non-const test: %d\n", *p6);
+// CHECK: Non-const test: 42
+
+// ============================================================================
+// Edge case tests
+// ============================================================================
+
+// Test 7: Repeated address-of reuses same definition
+int const *p7 = &Foo::bar;
+printf("Reuse test: %d\n", (*p == *p7) ? 1 : 0);
+// CHECK: Reuse test: 1
+
+%quit
diff --git a/clang/unittests/Interpreter/InterpreterTest.cpp b/clang/unittests/Interpreter/InterpreterTest.cpp
index 9ff9092524d21..341e61563e6bf 100644
--- a/clang/unittests/Interpreter/InterpreterTest.cpp
+++ b/clang/unittests/Interpreter/InterpreterTest.cpp
@@ -443,4 +443,18 @@ TEST_F(InterpreterTest, TranslationUnit_CanonicalDecl) {
             sema.getASTContext().getTranslationUnitDecl()->getCanonicalDecl());
 }
 
+TEST_F(InterpreterTest, StaticConstMemberAddress) {
+  std::unique_ptr<Interpreter> Interp = createInterpreter();
+
+  llvm::cantFail(
+      Interp->ParseAndExecute("struct Foo { static int const bar { 5 }; };"));
+
+  Value V;
+  llvm::cantFail(Interp->ParseAndExecute("int const * p = &Foo::bar; *p", &V));
+
+  ASSERT_TRUE(V.isValid());
+  ASSERT_TRUE(V.hasValue());
+  EXPECT_EQ(V.getInt(), 5);
+}
+
 } // end anonymous namespace

jeaye · 2025-11-26T20:08:15Z

@pfeodrippe I had a conversation with Vassil about this and cleared up that it's not something we can fix, since it's based on invalid C++ usage from the start. We can work around it in jank, though. We can close this PR!

pfeodrippe · 2025-11-26T22:44:43Z

@pfeodrippe I had a conversation with Vassil about this and cleared up that it's not something we can fix, since it's based on invalid C++ usage from the start. We can work around it in jank, though. We can close this PR!

Nice nice, thanks / Closing

pfeodrippe changed the title ~~Fix static const member address reference~~ [Clang] Fix static const member address reference Nov 23, 2025

pfeodrippe force-pushed the fix-static-const-member-address-reference branch 8 times, most recently from 8eaade1 to 6f6245e Compare November 25, 2025 01:55

Fix static const member address reference

0977736

pfeodrippe force-pushed the fix-static-const-member-address-reference branch from 6f6245e to 0977736 Compare November 25, 2025 02:08

tbaederr added the clang-repl label Nov 25, 2025

pfeodrippe marked this pull request as ready for review November 26, 2025 03:05

llvmbot added clang Clang issues not falling into any other category clang:codegen IR generation bugs: mangling, exceptions, etc. labels Nov 26, 2025

pfeodrippe closed this Nov 26, 2025

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