Automerge: [CIR] Finish global ctor init lowering (#162130)

andykaylor · github-actions[bot] · commit ee7ed16b6c8f · 2025-10-08T18:16:19.000Z
Implement support for creating a global ctor list during the
cir::LoweringPrepare pass, and add tests for lowering global
constructor-based initialization to LLVM IR.
diff --git a/clang/include/clang/CIR/Dialect/IR/CIRAttrs.td b/clang/include/clang/CIR/Dialect/IR/CIRAttrs.td
@@ -769,6 +769,51 @@ def CIR_VisibilityAttr : CIR_EnumAttr<CIR_VisibilityKind, "visibility"> {
   }];
 }
 
+//===----------------------------------------------------------------------===//
+// GloblCtorAttr
+//===----------------------------------------------------------------------===//
+
+class CIR_GlobalCtorDtor<string name, string attrMnemonic>
+    : CIR_Attr<"Global" # name, "global_" # attrMnemonic> {
+  let parameters = (ins "mlir::StringAttr":$name, "int":$priority);
+
+  let skipDefaultBuilders = 1;
+  let builders = [
+    AttrBuilder<(ins
+        "llvm::StringRef":$name,
+        CArg<"int", "65535">:$priority), [{
+      return $_get($_ctxt, mlir::StringAttr::get($_ctxt, name), priority);
+    }]>,
+    AttrBuilderWithInferredContext<(ins
+        "mlir::StringAttr":$name,
+        CArg<"int", "65535">:$priority), [{
+      return $_get(name.getContext(), name, priority);
+    }]>
+  ];
+
+  let assemblyFormat = [{
+    `<` $name `,` $priority `>`
+  }];
+
+  let extraClassDeclaration = [{
+    bool isDefaultPriority() const {
+      return getPriority() == getDefaultPriority();
+    };
+
+    static int getDefaultPriority() {
+      return 65535;
+    }
+  }];
+}
+
+def CIR_GlobalCtorAttr : CIR_GlobalCtorDtor<"Ctor", "ctor"> {
+  let summary = "Marks a function as a global constructor";
+  let description = [{
+    Marks the function as a global constructor in the module's constructor list.
+    It will be executed before main() is called.
+  }];
+}
+
 //===----------------------------------------------------------------------===//
 // BitfieldInfoAttr
 //===----------------------------------------------------------------------===//
diff --git a/clang/include/clang/CIR/Dialect/IR/CIRDialect.td b/clang/include/clang/CIR/Dialect/IR/CIRDialect.td
@@ -42,6 +42,7 @@ def CIR_Dialect : Dialect {
     static llvm::StringRef getNoThrowAttrName() { return "nothrow"; }
     static llvm::StringRef getSideEffectAttrName() { return "side_effect"; }
     static llvm::StringRef getModuleLevelAsmAttrName() { return "cir.module_asm"; }
+    static llvm::StringRef getGlobalCtorsAttrName() { return "cir.global_ctors"; }
 
     void registerAttributes();
     void registerTypes();
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 opGlobalDtorLowering() { return false; }
-  static bool opGlobalCtorAttr() { return false; }
   static bool opGlobalCtorPriority() { return false; }
   static bool opGlobalCtorList() { return false; }
   static bool setDSOLocal() { return false; }
diff --git a/clang/lib/CIR/Dialect/Transforms/LoweringPrepare.cpp b/clang/lib/CIR/Dialect/Transforms/LoweringPrepare.cpp
@@ -61,6 +61,9 @@ struct LoweringPreparePass : public LoweringPrepareBase<LoweringPreparePass> {
   /// Build a module init function that calls all the dynamic initializers.
   void buildCXXGlobalInitFunc();
 
+  /// Materialize global ctor/dtor list
+  void buildGlobalCtorDtorList();
+
   cir::FuncOp buildRuntimeFunction(
       mlir::OpBuilder &builder, llvm::StringRef name, mlir::Location loc,
       cir::FuncType type,
@@ -79,6 +82,9 @@ struct LoweringPreparePass : public LoweringPrepareBase<LoweringPreparePass> {
   llvm::StringMap<uint32_t> dynamicInitializerNames;
   llvm::SmallVector<cir::FuncOp> dynamicInitializers;
 
+  /// List of ctors and their priorities to be called before main()
+  llvm::SmallVector<std::pair<std::string, uint32_t>, 4> globalCtorList;
+
   void setASTContext(clang::ASTContext *c) { astCtx = c; }
 };
 
@@ -689,11 +695,36 @@ void LoweringPreparePass::lowerGlobalOp(GlobalOp op) {
   assert(!cir::MissingFeatures::opGlobalAnnotations());
 }
 
+template <typename AttributeTy>
+static llvm::SmallVector<mlir::Attribute>
+prepareCtorDtorAttrList(mlir::MLIRContext *context,
+                        llvm::ArrayRef<std::pair<std::string, uint32_t>> list) {
+  llvm::SmallVector<mlir::Attribute> attrs;
+  for (const auto &[name, priority] : list)
+    attrs.push_back(AttributeTy::get(context, name, priority));
+  return attrs;
+}
+
+void LoweringPreparePass::buildGlobalCtorDtorList() {
+  if (!globalCtorList.empty()) {
+    llvm::SmallVector<mlir::Attribute> globalCtors =
+        prepareCtorDtorAttrList<cir::GlobalCtorAttr>(&getContext(),
+                                                     globalCtorList);
+
+    mlirModule->setAttr(cir::CIRDialect::getGlobalCtorsAttrName(),
+                        mlir::ArrayAttr::get(&getContext(), globalCtors));
+  }
+
+  assert(!cir::MissingFeatures::opGlobalDtorLowering());
+}
+
 void LoweringPreparePass::buildCXXGlobalInitFunc() {
   if (dynamicInitializers.empty())
     return;
 
-  assert(!cir::MissingFeatures::opGlobalCtorList());
+  // TODO: handle globals with a user-specified initialzation priority.
+  // TODO: handle default priority more nicely.
+  assert(!cir::MissingFeatures::opGlobalCtorPriority());
 
   SmallString<256> fnName;
   // Include the filename in the symbol name. Including "sub_" matches gcc
@@ -722,6 +753,10 @@ void LoweringPreparePass::buildCXXGlobalInitFunc() {
   builder.setInsertionPointToStart(f.addEntryBlock());
   for (cir::FuncOp &f : dynamicInitializers)
     builder.createCallOp(f.getLoc(), f, {});
+  // Add the global init function (not the individual ctor functions) to the
+  // global ctor list.
+  globalCtorList.emplace_back(fnName,
+                              cir::GlobalCtorAttr::getDefaultPriority());
 
   cir::ReturnOp::create(builder, f.getLoc());
 }
@@ -852,6 +887,7 @@ void LoweringPreparePass::runOnOperation() {
     runOnOp(o);
 
   buildCXXGlobalInitFunc();
+  buildGlobalCtorDtorList();
 }
 
 std::unique_ptr<Pass> mlir::createLoweringPreparePass() {
diff --git a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
@@ -2413,6 +2413,73 @@ static void prepareTypeConverter(mlir::LLVMTypeConverter &converter,
   });
 }
 
+static void buildCtorDtorList(
+    mlir::ModuleOp module, StringRef globalXtorName, StringRef llvmXtorName,
+    llvm::function_ref<std::pair<StringRef, int>(mlir::Attribute)> createXtor) {
+  llvm::SmallVector<std::pair<StringRef, int>> globalXtors;
+  for (const mlir::NamedAttribute namedAttr : module->getAttrs()) {
+    if (namedAttr.getName() == globalXtorName) {
+      for (auto attr : mlir::cast<mlir::ArrayAttr>(namedAttr.getValue()))
+        globalXtors.emplace_back(createXtor(attr));
+      break;
+    }
+  }
+
+  if (globalXtors.empty())
+    return;
+
+  mlir::OpBuilder builder(module.getContext());
+  builder.setInsertionPointToEnd(&module.getBodyRegion().back());
+
+  // Create a global array llvm.global_ctors with element type of
+  // struct { i32, ptr, ptr }
+  auto ctorPFTy = mlir::LLVM::LLVMPointerType::get(builder.getContext());
+  llvm::SmallVector<mlir::Type> ctorStructFields;
+  ctorStructFields.push_back(builder.getI32Type());
+  ctorStructFields.push_back(ctorPFTy);
+  ctorStructFields.push_back(ctorPFTy);
+
+  auto ctorStructTy = mlir::LLVM::LLVMStructType::getLiteral(
+      builder.getContext(), ctorStructFields);
+  auto ctorStructArrayTy =
+      mlir::LLVM::LLVMArrayType::get(ctorStructTy, globalXtors.size());
+
+  mlir::Location loc = module.getLoc();
+  auto newGlobalOp = mlir::LLVM::GlobalOp::create(
+      builder, loc, ctorStructArrayTy, /*constant=*/false,
+      mlir::LLVM::Linkage::Appending, llvmXtorName, mlir::Attribute());
+
+  builder.createBlock(&newGlobalOp.getRegion());
+  builder.setInsertionPointToEnd(newGlobalOp.getInitializerBlock());
+
+  mlir::Value result =
+      mlir::LLVM::UndefOp::create(builder, loc, ctorStructArrayTy);
+
+  for (auto [index, fn] : llvm::enumerate(globalXtors)) {
+    mlir::Value structInit =
+        mlir::LLVM::UndefOp::create(builder, loc, ctorStructTy);
+    mlir::Value initPriority = mlir::LLVM::ConstantOp::create(
+        builder, loc, ctorStructFields[0], fn.second);
+    mlir::Value initFuncAddr = mlir::LLVM::AddressOfOp::create(
+        builder, loc, ctorStructFields[1], fn.first);
+    mlir::Value initAssociate =
+        mlir::LLVM::ZeroOp::create(builder, loc, ctorStructFields[2]);
+    // Literal zero makes the InsertValueOp::create ambiguous.
+    llvm::SmallVector<int64_t> zero{0};
+    structInit = mlir::LLVM::InsertValueOp::create(builder, loc, structInit,
+                                                   initPriority, zero);
+    structInit = mlir::LLVM::InsertValueOp::create(builder, loc, structInit,
+                                                   initFuncAddr, 1);
+    // TODO: handle associated data for initializers.
+    structInit = mlir::LLVM::InsertValueOp::create(builder, loc, structInit,
+                                                   initAssociate, 2);
+    result = mlir::LLVM::InsertValueOp::create(builder, loc, result, structInit,
+                                               index);
+  }
+
+  builder.create<mlir::LLVM::ReturnOp>(loc, result);
+}
+
 // The applyPartialConversion function traverses blocks in the dominance order,
 // so it does not lower and operations that are not reachachable from the
 // operations passed in as arguments. Since we do need to lower such code in
@@ -2519,6 +2586,14 @@ void ConvertCIRToLLVMPass::runOnOperation() {
 
   if (failed(applyPartialConversion(ops, target, std::move(patterns))))
     signalPassFailure();
+
+  // Emit the llvm.global_ctors array.
+  buildCtorDtorList(module, cir::CIRDialect::getGlobalCtorsAttrName(),
+                    "llvm.global_ctors", [](mlir::Attribute attr) {
+                      auto ctorAttr = mlir::cast<cir::GlobalCtorAttr>(attr);
+                      return std::make_pair(ctorAttr.getName(),
+                                            ctorAttr.getPriority());
+                    });
 }
 
 mlir::LogicalResult CIRToLLVMBrOpLowering::matchAndRewrite(
diff --git a/clang/test/CIR/CodeGen/global-init.cpp b/clang/test/CIR/CodeGen/global-init.cpp
@@ -1,9 +1,10 @@
 // RUN: %clang_cc1 -std=c++17 -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
-
-// Note: The LoweringPrepare work isn't yet complete. We still need to create
-//       the global ctor list attribute.
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm %s -o %t-cir.ll
+// RUN: FileCheck --input-file=%t-cir.ll %s --check-prefix=LLVM
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-unknown-linux-gnu -emit-llvm %s -o %t.ll
+// RUN: FileCheck --input-file=%t.ll %s --check-prefix=OGCG
 
 struct NeedsCtor {
   NeedsCtor();
@@ -15,6 +16,9 @@ NeedsCtor needsCtor;
 // CIR-BEFORE-LPP:   %[[THIS:.*]] = cir.get_global @needsCtor : !cir.ptr<!rec_NeedsCtor>
 // CIR-BEFORE-LPP:   cir.call @_ZN9NeedsCtorC1Ev(%[[THIS]]) : (!cir.ptr<!rec_NeedsCtor>) -> ()
 
+// CIR: module @{{.*}} attributes {
+// CIR-SAME: cir.global_ctors = [#cir.global_ctor<"_GLOBAL__sub_I_[[FILENAME:.*]]", 65535>]
+
 // CIR: cir.global external @needsCtor = #cir.zero : !rec_NeedsCtor
 // CIR: cir.func internal private @__cxx_global_var_init() {
 // CIR:   %0 = cir.get_global @needsCtor : !cir.ptr<!rec_NeedsCtor>
@@ -24,3 +28,22 @@ NeedsCtor needsCtor;
 // CIR:   cir.call @__cxx_global_var_init() : () -> ()
 // CIR:   cir.return
 // CIR: }
+
+// LLVM: @needsCtor = global %struct.NeedsCtor zeroinitializer, align 1
+// LLVM: @llvm.global_ctors = appending global [1 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 65535, ptr @_GLOBAL__sub_I_[[FILENAME:.*]], ptr null }]
+// LLVM: declare void @_ZN9NeedsCtorC1Ev(ptr)
+
+// LLVM: define internal void @__cxx_global_var_init()
+// LLVM:   call void @_ZN9NeedsCtorC1Ev(ptr @needsCtor)
+
+// LLVM: define void @_GLOBAL__sub_I_[[FILENAME]]()
+// LLVM:   call void @__cxx_global_var_init()
+
+// OGCG: @needsCtor = global %struct.NeedsCtor zeroinitializer, align 1
+// OGCG: @llvm.global_ctors = appending global [1 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 65535, ptr @_GLOBAL__sub_I_[[FILENAME:.*]], ptr null }]
+
+// OGCG: define internal void @__cxx_global_var_init() {{.*}} section ".text.startup" {
+// OGCG:   call void @_ZN9NeedsCtorC1Ev(ptr noundef nonnull align 1 dereferenceable(1) @needsCtor)
+
+// OGCG: define internal void @_GLOBAL__sub_I_[[FILENAME]]() {{.*}} section ".text.startup" {
+// OGCG:   call void @__cxx_global_var_init()
