[Clang] [C++26] Expansion Statements (Part 8: Codegen)

clang/lib/CodeGen/CGDecl.cpp

@@ -143,8 +143,12 @@ void CodeGenFunction::EmitDecl(const Decl &D, bool EvaluateConditionDecl) {
     // None of these decls require codegen support.
     return;
 
-  case Decl::CXXExpansionStmt:
-    llvm_unreachable("TODO");
+  case Decl::CXXExpansionStmt: {
+    const auto *ESD = cast<CXXExpansionStmtDecl>(&D);
+    assert(ESD->getInstantiations() && "expansion statement not expanded?");
+    EmitStmt(ESD->getInstantiations());
+    return;
+  }
 
   case Decl::NamespaceAlias:
     if (CGDebugInfo *DI = getDebugInfo())

clang/lib/CodeGen/CGStmt.cpp

@@ -210,7 +210,8 @@ void CodeGenFunction::EmitStmt(const Stmt *S, ArrayRef<const Attr *> Attrs) {
   case Stmt::CXXDependentExpansionStmtPatternClass:
     llvm_unreachable("unexpanded expansion statements should not be emitted");
   case Stmt::CXXExpansionStmtInstantiationClass:
-    llvm_unreachable("Todo");
+    EmitCXXExpansionStmtInstantiation(cast<CXXExpansionStmtInstantiation>(*S));
+    break;
   case Stmt::SEHTryStmtClass:
     EmitSEHTryStmt(cast<SEHTryStmt>(*S));
     break;
@@ -1563,6 +1564,44 @@ CodeGenFunction::EmitCXXForRangeStmt(const CXXForRangeStmt &S,
   }
 }
 
+void CodeGenFunction::EmitCXXExpansionStmtInstantiation(
+    const CXXExpansionStmtInstantiation &S) {
+  // FIXME: For reasons beyond my understanding, two scopes are required to emit
+  // the destructors of lifetime-extended temporaries in the right place, but
+  // only in some templates. There are some other issues with lifetime-extended
+  // temporaries currently (https://github.com/llvm/llvm-project/issues/165182);
+  // perhaps resolving those will allow us to remove the second scope here
+  // because there really ought to be a better way of doing this.
+  LexicalScope Scope(*this, S.getSourceRange());
+  LexicalScope Scope2(*this, S.getSourceRange());
+
+  for (const Stmt *DS : S.getSharedStmts())
+    EmitStmt(DS);
+
+  if (S.getInstantiations().empty() || !HaveInsertPoint())
+    return;
+
+  JumpDest ExpandExit = getJumpDestInCurrentScope("expand.end");
+  JumpDest ContinueDest;
+  for (auto [N, Inst] : enumerate(S.getInstantiations())) {
+    if (!HaveInsertPoint()) {
+      EmitBlock(ExpandExit.getBlock(), true);
+      return;
+    }
+
+    if (N == S.getInstantiations().size() - 1)
+      ContinueDest = ExpandExit;
+    else
+      ContinueDest = getJumpDestInCurrentScope("expand.next");
+
+    LexicalScope ExpansionScope(*this, S.getSourceRange());
+    BreakContinueStack.push_back(BreakContinue(S, ExpandExit, ContinueDest));
+    EmitStmt(Inst);
+    BreakContinueStack.pop_back();
+    EmitBlock(ContinueDest.getBlock(), true);
+  }
+}
+
 void CodeGenFunction::EmitReturnOfRValue(RValue RV, QualType Ty) {
   if (RV.isScalar()) {
     Builder.CreateStore(RV.getScalarVal(), ReturnValue);

clang/lib/CodeGen/CodeGenFunction.h

@@ -3690,6 +3690,9 @@ class CodeGenFunction : public CodeGenTypeCache {
   void EmitCXXForRangeStmt(const CXXForRangeStmt &S,
                            ArrayRef<const Attr *> Attrs = {});
 
+  void
+  EmitCXXExpansionStmtInstantiation(const CXXExpansionStmtInstantiation &S);
+
   /// Controls insertion of cancellation exit blocks in worksharing constructs.
   class OMPCancelStackRAII {
     CodeGenFunction &CGF;