[CIR] Add support for global ctor/dtor attributes (#163247)

andykaylor · web-flow · commit 645745f9de7e · 2025-10-13T17:07:05.000-07:00
This adds support for adding the `global_ctor` or `global_dtor`
attribute to the CIR representation of functions defined with
`__attribute__((constructor))` or `__attribute__((destructor))` and
adding them to the `@llvm.global_ctors` or `@llvm.global_dtors` list
during lowering to LLVM IR.
diff --git a/clang/include/clang/CIR/Dialect/IR/CIRAttrs.td b/clang/include/clang/CIR/Dialect/IR/CIRAttrs.td
@@ -814,6 +814,14 @@ def CIR_GlobalCtorAttr : CIR_GlobalCtorDtor<"Ctor", "ctor"> {
   }];
 }
 
+def CIR_GlobalDtorAttr : CIR_GlobalCtorDtor<"Dtor", "dtor"> {
+  let summary = "Marks a function as a global destructor";
+  let description = [{
+      Marks a function as a global destructor in the module dtors list.
+      The function will be executed before the module unloading.
+  }];
+}
+
 //===----------------------------------------------------------------------===//
 // BitfieldInfoAttr
 //===----------------------------------------------------------------------===//
diff --git a/clang/include/clang/CIR/Dialect/IR/CIRDialect.td b/clang/include/clang/CIR/Dialect/IR/CIRDialect.td
@@ -43,6 +43,7 @@ def CIR_Dialect : Dialect {
     static llvm::StringRef getSideEffectAttrName() { return "side_effect"; }
     static llvm::StringRef getModuleLevelAsmAttrName() { return "cir.module_asm"; }
     static llvm::StringRef getGlobalCtorsAttrName() { return "cir.global_ctors"; }
+    static llvm::StringRef getGlobalDtorsAttrName() { return "cir.global_dtors"; }
 
     void registerAttributes();
     void registerTypes();
diff --git a/clang/include/clang/CIR/Dialect/IR/CIROps.td b/clang/include/clang/CIR/Dialect/IR/CIROps.td
@@ -88,6 +88,19 @@ class CIR_Op<string mnemonic, list<Trait> traits = []> :
   code extraLLVMLoweringPatternDecl = "";
 }
 
+//===----------------------------------------------------------------------===//
+// CIR Operation Traits
+//===----------------------------------------------------------------------===//
+
+class HasAtMostOneOfAttrsPred<list<string> names> :
+  CPred<!foldl("0", names, acc, name,  acc # " + (" # name # " ? 1 : 0)")
+        # " <= 1">;
+
+class HasAtMostOneOfAttrs<list<string> names> : PredOpTrait<
+  "has only one of the optional attributes: " # !interleave(names, ", "),
+  HasAtMostOneOfAttrsPred<!foreach(name, names, "$" # name)>
+>;
+
 //===----------------------------------------------------------------------===//
 // CastOp
 //===----------------------------------------------------------------------===//
@@ -2422,9 +2435,17 @@ def CIR_GetMemberOp : CIR_Op<"get_member"> {
 // TODO(CIR): FuncOp is still a tiny shell of what it will become.  Many more
 // properties and attributes will be added as upstreaming continues.
 
+def CIR_OptionalPriorityAttr : OptionalAttr<
+  DefaultValuedAttr<
+    ConfinedAttr<I32Attr, [IntMinValue<101>, IntMaxValue<65535>]>,
+    "65535"
+  >
+>;
+
 def CIR_FuncOp : CIR_Op<"func", [
   AutomaticAllocationScope, CallableOpInterface, FunctionOpInterface,
   DeclareOpInterfaceMethods<CIRGlobalValueInterface>,
+  HasAtMostOneOfAttrs<["global_ctor_priority", "global_dtor_priority"]>,
   IsolatedFromAbove
 ]> {
   let summary = "Declare or define a function";
@@ -2449,6 +2470,12 @@ def CIR_FuncOp : CIR_Op<"func", [
     without a prototype and, consequently, may contain calls with invalid
     arguments and undefined behavior.
 
+    The `global_ctor` keyword indicates whether a function should execute before
+    `main()` function, as specified by `__attribute__((constructor))`. An
+    execution priority can also be specified `global_ctor(<priority>)`.
+    Similarly, for global destructors both `global_dtor` and
+    `global_dtor(<priority>)` are available.
+
     Example:
 
     ```mlir
@@ -2487,7 +2514,9 @@ def CIR_FuncOp : CIR_Op<"func", [
                        UnitAttr:$comdat,
                        OptionalAttr<DictArrayAttr>:$arg_attrs,
                        OptionalAttr<DictArrayAttr>:$res_attrs,
-                       OptionalAttr<FlatSymbolRefAttr>:$aliasee);
+                       OptionalAttr<FlatSymbolRefAttr>:$aliasee,
+                       CIR_OptionalPriorityAttr:$global_ctor_priority,
+                       CIR_OptionalPriorityAttr:$global_dtor_priority);
 
   let regions = (region AnyRegion:$body);
 
diff --git a/clang/include/clang/CIR/MissingFeatures.h b/clang/include/clang/CIR/MissingFeatures.h
@@ -39,7 +39,6 @@ struct MissingFeatures {
   static bool opGlobalUsedOrCompilerUsed() { return false; }
   static bool opGlobalAnnotations() { return false; }
   static bool opGlobalCtorPriority() { return false; }
-  static bool opGlobalDtorList() { return false; }
   static bool setDSOLocal() { return false; }
   static bool setComdat() { return false; }
 
@@ -175,6 +174,10 @@ struct MissingFeatures {
   static bool atomicScope() { return false; }
   static bool atomicSyncScopeID() { return false; }
 
+  // Global ctor handling
+  static bool globalCtorLexOrder() { return false; }
+  static bool globalCtorAssociatedData() { return false; }
+
   // Misc
   static bool abiArgInfo() { return false; }
   static bool addHeapAllocSiteMetadata() { return false; }
diff --git a/clang/lib/CIR/CodeGen/CIRGenModule.cpp b/clang/lib/CIR/CodeGen/CIRGenModule.cpp
@@ -451,15 +451,47 @@ void CIRGenModule::emitGlobalFunctionDefinition(clang::GlobalDecl gd,
   setNonAliasAttributes(gd, funcOp);
   assert(!cir::MissingFeatures::opFuncAttributesForDefinition());
 
-  if (funcDecl->getAttr<ConstructorAttr>())
-    errorNYI(funcDecl->getSourceRange(), "constructor attribute");
-  if (funcDecl->getAttr<DestructorAttr>())
-    errorNYI(funcDecl->getSourceRange(), "destructor attribute");
+  auto getPriority = [this](const auto *attr) -> int {
+    Expr *e = attr->getPriority();
+    if (e)
+      return e->EvaluateKnownConstInt(this->getASTContext()).getExtValue();
+    return attr->DefaultPriority;
+  };
+
+  if (const ConstructorAttr *ca = funcDecl->getAttr<ConstructorAttr>())
+    addGlobalCtor(funcOp, getPriority(ca));
+  if (const DestructorAttr *da = funcDecl->getAttr<DestructorAttr>())
+    addGlobalDtor(funcOp, getPriority(da));
 
   if (funcDecl->getAttr<AnnotateAttr>())
     errorNYI(funcDecl->getSourceRange(), "deferredAnnotations");
 }
 
+/// Track functions to be called before main() runs.
+void CIRGenModule::addGlobalCtor(cir::FuncOp ctor,
+                                 std::optional<int> priority) {
+  assert(!cir::MissingFeatures::globalCtorLexOrder());
+  assert(!cir::MissingFeatures::globalCtorAssociatedData());
+
+  // Traditional LLVM codegen directly adds the function to the list of global
+  // ctors. In CIR we just add a global_ctor attribute to the function. The
+  // global list is created in LoweringPrepare.
+  //
+  // FIXME(from traditional LLVM): Type coercion of void()* types.
+  ctor.setGlobalCtorPriority(priority);
+}
+
+/// Add a function to the list that will be called when the module is unloaded.
+void CIRGenModule::addGlobalDtor(cir::FuncOp dtor,
+                                 std::optional<int> priority) {
+  if (codeGenOpts.RegisterGlobalDtorsWithAtExit &&
+      (!getASTContext().getTargetInfo().getTriple().isOSAIX()))
+    errorNYI(dtor.getLoc(), "registerGlobalDtorsWithAtExit");
+
+  // FIXME(from traditional LLVM): Type coercion of void()* types.
+  dtor.setGlobalDtorPriority(priority);
+}
+
 void CIRGenModule::handleCXXStaticMemberVarInstantiation(VarDecl *vd) {
   VarDecl::DefinitionKind dk = vd->isThisDeclarationADefinition();
   if (dk == VarDecl::Definition && vd->hasAttr<DLLImportAttr>())
diff --git a/clang/lib/CIR/CodeGen/CIRGenModule.h b/clang/lib/CIR/CodeGen/CIRGenModule.h
@@ -159,6 +159,13 @@ class CIRGenModule : public CIRGenTypeCache {
                                       bool isConstant = false,
                                       mlir::Operation *insertPoint = nullptr);
 
+  /// Add a global constructor or destructor to the module.
+  /// The priority is optional, if not specified, the default priority is used.
+  void addGlobalCtor(cir::FuncOp ctor,
+                     std::optional<int> priority = std::nullopt);
+  void addGlobalDtor(cir::FuncOp dtor,
+                     std::optional<int> priority = std::nullopt);
+
   bool shouldZeroInitPadding() const {
     // In C23 (N3096) $6.7.10:
     // """
diff --git a/clang/lib/CIR/Dialect/IR/CIRDialect.cpp b/clang/lib/CIR/Dialect/IR/CIRDialect.cpp
@@ -15,6 +15,7 @@
 #include "clang/CIR/Dialect/IR/CIROpsEnums.h"
 #include "clang/CIR/Dialect/IR/CIRTypes.h"
 
+#include "mlir/IR/DialectImplementation.h"
 #include "mlir/Interfaces/ControlFlowInterfaces.h"
 #include "mlir/Interfaces/FunctionImplementation.h"
 #include "mlir/Support/LLVM.h"
@@ -1720,6 +1721,43 @@ ParseResult cir::FuncOp::parse(OpAsmParser &parser, OperationState &state) {
     hasAlias = true;
   }
 
+  auto parseGlobalDtorCtor =
+      [&](StringRef keyword,
+          llvm::function_ref<void(std::optional<int> prio)> createAttr)
+      -> mlir::LogicalResult {
+    if (mlir::succeeded(parser.parseOptionalKeyword(keyword))) {
+      std::optional<int> priority;
+      if (mlir::succeeded(parser.parseOptionalLParen())) {
+        auto parsedPriority = mlir::FieldParser<int>::parse(parser);
+        if (mlir::failed(parsedPriority))
+          return parser.emitError(parser.getCurrentLocation(),
+                                  "failed to parse 'priority', of type 'int'");
+        priority = parsedPriority.value_or(int());
+        // Parse literal ')'
+        if (parser.parseRParen())
+          return failure();
+      }
+      createAttr(priority);
+    }
+    return success();
+  };
+
+  if (parseGlobalDtorCtor("global_ctor", [&](std::optional<int> priority) {
+        mlir::IntegerAttr globalCtorPriorityAttr =
+            builder.getI32IntegerAttr(priority.value_or(65535));
+        state.addAttribute(getGlobalCtorPriorityAttrName(state.name),
+                           globalCtorPriorityAttr);
+      }).failed())
+    return failure();
+
+  if (parseGlobalDtorCtor("global_dtor", [&](std::optional<int> priority) {
+        mlir::IntegerAttr globalDtorPriorityAttr =
+            builder.getI32IntegerAttr(priority.value_or(65535));
+        state.addAttribute(getGlobalDtorPriorityAttrName(state.name),
+                           globalDtorPriorityAttr);
+      }).failed())
+    return failure();
+
   // Parse the optional function body.
   auto *body = state.addRegion();
   OptionalParseResult parseResult = parser.parseOptionalRegion(
@@ -1801,6 +1839,18 @@ void cir::FuncOp::print(OpAsmPrinter &p) {
     p << ")";
   }
 
+  if (auto globalCtorPriority = getGlobalCtorPriority()) {
+    p << " global_ctor";
+    if (globalCtorPriority.value() != 65535)
+      p << "(" << globalCtorPriority.value() << ")";
+  }
+
+  if (auto globalDtorPriority = getGlobalDtorPriority()) {
+    p << " global_dtor";
+    if (globalDtorPriority.value() != 65535)
+      p << "(" << globalDtorPriority.value() << ")";
+  }
+
   // Print the body if this is not an external function.
   Region &body = getOperation()->getRegion(0);
   if (!body.empty()) {
diff --git a/clang/lib/CIR/Dialect/Transforms/LoweringPrepare.cpp b/clang/lib/CIR/Dialect/Transforms/LoweringPrepare.cpp
@@ -105,6 +105,8 @@ struct LoweringPreparePass : public LoweringPrepareBase<LoweringPreparePass> {
 
   /// List of ctors and their priorities to be called before main()
   llvm::SmallVector<std::pair<std::string, uint32_t>, 4> globalCtorList;
+  /// List of dtors and their priorities to be called when unloading module.
+  llvm::SmallVector<std::pair<std::string, uint32_t>, 4> globalDtorList;
 
   void setASTContext(clang::ASTContext *c) {
     astCtx = c;
@@ -823,10 +825,13 @@ void LoweringPreparePass::buildGlobalCtorDtorList() {
                         mlir::ArrayAttr::get(&getContext(), globalCtors));
   }
 
-  // We will eventual need to populate a global_dtor list, but that's not
-  // needed for globals with destructors. It will only be needed for functions
-  // that are marked as global destructors with an attribute.
-  assert(!cir::MissingFeatures::opGlobalDtorList());
+  if (!globalDtorList.empty()) {
+    llvm::SmallVector<mlir::Attribute> globalDtors =
+        prepareCtorDtorAttrList<cir::GlobalDtorAttr>(&getContext(),
+                                                     globalDtorList);
+    mlirModule->setAttr(cir::CIRDialect::getGlobalDtorsAttrName(),
+                        mlir::ArrayAttr::get(&getContext(), globalDtors));
+  }
 }
 
 void LoweringPreparePass::buildCXXGlobalInitFunc() {
@@ -975,22 +980,28 @@ void LoweringPreparePass::lowerArrayCtor(cir::ArrayCtor op) {
 }
 
 void LoweringPreparePass::runOnOp(mlir::Operation *op) {
-  if (auto arrayCtor = dyn_cast<ArrayCtor>(op))
+  if (auto arrayCtor = dyn_cast<cir::ArrayCtor>(op)) {
     lowerArrayCtor(arrayCtor);
-  else if (auto arrayDtor = dyn_cast<cir::ArrayDtor>(op))
+  } else if (auto arrayDtor = dyn_cast<cir::ArrayDtor>(op)) {
     lowerArrayDtor(arrayDtor);
-  else if (auto cast = mlir::dyn_cast<cir::CastOp>(op))
+  } else if (auto cast = mlir::dyn_cast<cir::CastOp>(op)) {
     lowerCastOp(cast);
-  else if (auto complexDiv = mlir::dyn_cast<cir::ComplexDivOp>(op))
+  } else if (auto complexDiv = mlir::dyn_cast<cir::ComplexDivOp>(op)) {
     lowerComplexDivOp(complexDiv);
-  else if (auto complexMul = mlir::dyn_cast<cir::ComplexMulOp>(op))
+  } else if (auto complexMul = mlir::dyn_cast<cir::ComplexMulOp>(op)) {
     lowerComplexMulOp(complexMul);
-  else if (auto glob = mlir::dyn_cast<cir::GlobalOp>(op))
+  } else if (auto glob = mlir::dyn_cast<cir::GlobalOp>(op)) {
     lowerGlobalOp(glob);
-  else if (auto dynamicCast = mlir::dyn_cast<cir::DynamicCastOp>(op))
+  } else if (auto dynamicCast = mlir::dyn_cast<cir::DynamicCastOp>(op)) {
     lowerDynamicCastOp(dynamicCast);
-  else if (auto unary = mlir::dyn_cast<cir::UnaryOp>(op))
+  } else if (auto unary = mlir::dyn_cast<cir::UnaryOp>(op)) {
     lowerUnaryOp(unary);
+  } else if (auto fnOp = dyn_cast<cir::FuncOp>(op)) {
+    if (auto globalCtor = fnOp.getGlobalCtorPriority())
+      globalCtorList.emplace_back(fnOp.getName(), globalCtor.value());
+    else if (auto globalDtor = fnOp.getGlobalDtorPriority())
+      globalDtorList.emplace_back(fnOp.getName(), globalDtor.value());
+  }
 }
 
 void LoweringPreparePass::runOnOperation() {
@@ -1003,7 +1014,7 @@ void LoweringPreparePass::runOnOperation() {
   op->walk([&](mlir::Operation *op) {
     if (mlir::isa<cir::ArrayCtor, cir::ArrayDtor, cir::CastOp,
                   cir::ComplexMulOp, cir::ComplexDivOp, cir::DynamicCastOp,
-                  cir::GlobalOp, cir::UnaryOp>(op))
+                  cir::FuncOp, cir::GlobalOp, cir::UnaryOp>(op))
       opsToTransform.push_back(op);
   });
 
diff --git a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
@@ -2598,7 +2598,13 @@ void ConvertCIRToLLVMPass::runOnOperation() {
                       return std::make_pair(ctorAttr.getName(),
                                             ctorAttr.getPriority());
                     });
-  assert(!cir::MissingFeatures::opGlobalDtorList());
+  // Emit the llvm.global_dtors array.
+  buildCtorDtorList(module, cir::CIRDialect::getGlobalDtorsAttrName(),
+                    "llvm.global_dtors", [](mlir::Attribute attr) {
+                      auto dtorAttr = mlir::cast<cir::GlobalDtorAttr>(attr);
+                      return std::make_pair(dtorAttr.getName(),
+                                            dtorAttr.getPriority());
+                    });
 }
 
 mlir::LogicalResult CIRToLLVMBrOpLowering::matchAndRewrite(
diff --git a/clang/test/CIR/CodeGen/global-ctor-dtor.cpp b/clang/test/CIR/CodeGen/global-ctor-dtor.cpp
@@ -0,0 +1,45 @@
+// RUN: %clang_cc1 -std=c++20 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir -mmlir --mlir-print-ir-before=cir-lowering-prepare %s -o %t.cir 2> %t-before.cir
+// RUN: FileCheck --input-file=%t-before.cir %s --check-prefix=CIR-BEFORE-LPP
+// RUN: FileCheck --input-file=%t.cir %s --check-prefix=CIR-AFTER
+// RUN: FileCheck --check-prefix=CIR-AFTER --input-file=%t.cir %s
+// RUN: %clang_cc1 -std=c++20 -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm %s -o %t-cir.ll
+// RUN: FileCheck --check-prefix=LLVM --input-file=%t-cir.ll %s
+// RUN: %clang_cc1 -std=c++20 -triple x86_64-unknown-linux-gnu -emit-llvm %s -o %t.ll
+// RUN: FileCheck --check-prefix=OGCG --input-file=%t.ll %s
+
+extern int bar();
+void foo(void) __attribute__((constructor));
+void foo(void) {
+  bar();
+}
+
+// CIR-BEFORE-LPP: cir.func dso_local @_Z3foov() global_ctor
+
+void foo2(void) __attribute__((constructor(777)));
+void foo2(void) {
+  bar();
+}
+
+// CIR-BEFORE-LPP: cir.func dso_local @_Z4foo2v() global_ctor(777)
+
+void foo3(void) __attribute__((destructor));
+void foo3(void) {
+  bar();
+}
+
+// CIR-BEFORE-LPP: cir.func dso_local @_Z4foo3v() global_dtor
+
+void foo4(void) __attribute__((destructor(789)));
+void foo4(void) {
+  bar();
+}
+
+// CIR-BEFORE-LPP: cir.func dso_local @_Z4foo4v() global_dtor(789)
+
+// CIR-AFTER: module @{{.*}} attributes {cir.global_ctors = [#cir.global_ctor<"_Z3foov", 65535>, #cir.global_ctor<"_Z4foo2v", 777>], cir.global_dtors = [#cir.global_dtor<"_Z4foo3v", 65535>, #cir.global_dtor<"_Z4foo4v", 789>]
+
+// LLVM: @llvm.global_ctors = appending global [2 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 65535, ptr @_Z3foov, ptr null }, { i32, ptr, ptr } { i32 777, ptr @_Z4foo2v, ptr null }]
+// LLVM: @llvm.global_dtors = appending global [2 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 65535, ptr @_Z4foo3v, ptr null }, { i32, ptr, ptr } { i32 789, ptr @_Z4foo4v, ptr null }]
+
+// OGCG: @llvm.global_ctors = appending global [2 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 65535, ptr @_Z3foov, ptr null }, { i32, ptr, ptr } { i32 777, ptr @_Z4foo2v, ptr null }]
+// OGCG: @llvm.global_dtors = appending global [2 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 65535, ptr @_Z4foo3v, ptr null }, { i32, ptr, ptr } { i32 789, ptr @_Z4foo4v, ptr null }]
diff --git a/clang/test/CIR/IR/func.cir b/clang/test/CIR/IR/func.cir
