[CIR][CIRGen] Add codegen for global compound literals (#454)

This PR adds support for global compound literals. 
The implementation is almost the same as in original codegen. But the
original codegen can reuse the value of emitted compound literal global
variable in case then the init expression of new variable and this
variable are the same.
It's easy to implement this feature. But I can't find any test-case then
this feature will be applied. So I decided to ignore this optimization
opportunity to avoid mistakes.

clang/lib/CIR/CodeGen/CIRGenCstEmitter.h

@@ -67,9 +67,14 @@ class ConstantEmitter {
   /// Is the current emission context abstract?
   bool isAbstract() const { return Abstract; }
 
+  bool isInConstantContext() const { return InConstantContext; }
+  void setInConstantContext(bool var) { InConstantContext = var; }
+
   /// Try to emit the initiaizer of the given declaration as an abstract
   /// constant.  If this succeeds, the emission must be finalized.
   mlir::Attribute tryEmitForInitializer(const VarDecl &D);
+  mlir::Attribute tryEmitForInitializer(const Expr *E, LangAS destAddrSpace,
+                                        QualType destType);
 
   void finalize(mlir::cir::GlobalOp global);
 
@@ -106,6 +111,8 @@ class ConstantEmitter {
   mlir::Attribute emitAbstract(SourceLocation loc, const APValue &value,
                                QualType T);
 
+  mlir::Attribute tryEmitConstantExpr(const ConstantExpr *CE);
+
   // These are private helper routines of the constant emitter that
   // can't actually be private because things are split out into helper
   // functions and classes.

clang/lib/CIR/CodeGen/CIRGenExprConst.cpp

@@ -840,8 +840,9 @@ class ConstExprEmitter
   mlir::Attribute VisitStmt(Stmt *S, QualType T) { return nullptr; }
 
   mlir::Attribute VisitConstantExpr(ConstantExpr *CE, QualType T) {
-    assert(0 && "unimplemented");
-    return {};
+    if (mlir::Attribute Result = Emitter.tryEmitConstantExpr(CE))
+      return Result;
+    return Visit(CE->getSubExpr(), T);
   }
 
   mlir::Attribute VisitParenExpr(ParenExpr *PE, QualType T) {
@@ -1368,15 +1369,44 @@ ConstantLValueEmitter::tryEmitBase(const APValue::LValueBase &base) {
   return Visit(base.get<const Expr *>());
 }
 
+static ConstantLValue
+tryEmitGlobalCompoundLiteral(ConstantEmitter &emitter,
+                             const CompoundLiteralExpr *E) {
+  CIRGenModule &CGM = emitter.CGM;
+
+  LangAS addressSpace = E->getType().getAddressSpace();
+  mlir::Attribute C = emitter.tryEmitForInitializer(E->getInitializer(),
+                                                    addressSpace, E->getType());
+  if (!C) {
+    assert(!E->isFileScope() &&
+           "file-scope compound literal did not have constant initializer!");
+    return nullptr;
+  }
+
+  auto GV = CIRGenModule::createGlobalOp(
+      CGM, CGM.getLoc(E->getSourceRange()),
+      CGM.createGlobalCompoundLiteralName(),
+      CGM.getTypes().convertTypeForMem(E->getType()),
+      E->getType().isConstantStorage(CGM.getASTContext(), false, false));
+  GV.setInitialValueAttr(C);
+  GV.setLinkage(mlir::cir::GlobalLinkageKind::InternalLinkage);
+  CharUnits Align = CGM.getASTContext().getTypeAlignInChars(E->getType());
+  GV.setAlignment(Align.getAsAlign().value());
+
+  emitter.finalize(GV);
+  return CGM.getBuilder().getGlobalViewAttr(GV);
+}
+
 ConstantLValue ConstantLValueEmitter::VisitConstantExpr(const ConstantExpr *E) {
   assert(0 && "NYI");
   return Visit(E->getSubExpr());
 }
 
 ConstantLValue
 ConstantLValueEmitter::VisitCompoundLiteralExpr(const CompoundLiteralExpr *E) {
-  assert(0 && "NYI");
-  return nullptr;
+  ConstantEmitter CompoundLiteralEmitter(CGM, Emitter.CGF);
+  CompoundLiteralEmitter.setInConstantContext(Emitter.isInConstantContext());
+  return tryEmitGlobalCompoundLiteral(CompoundLiteralEmitter, E);
 }
 
 ConstantLValue
@@ -1457,6 +1487,13 @@ mlir::Attribute ConstantEmitter::tryEmitForInitializer(const VarDecl &D) {
   return markIfFailed(tryEmitPrivateForVarInit(D));
 }
 
+mlir::Attribute ConstantEmitter::tryEmitForInitializer(const Expr *E,
+                                                       LangAS destAddrSpace,
+                                                       QualType destType) {
+  initializeNonAbstract(destAddrSpace);
+  return markIfFailed(tryEmitPrivateForMemory(E, destType));
+}
+
 void ConstantEmitter::finalize(mlir::cir::GlobalOp global) {
   assert(InitializedNonAbstract &&
          "finalizing emitter that was used for abstract emission?");
@@ -1549,6 +1586,17 @@ mlir::Attribute ConstantEmitter::tryEmitAbstract(const APValue &value,
   return validateAndPopAbstract(C, state);
 }
 
+mlir::Attribute ConstantEmitter::tryEmitConstantExpr(const ConstantExpr *CE) {
+  if (!CE->hasAPValueResult())
+    return nullptr;
+
+  QualType RetType = CE->getType();
+  if (CE->isGLValue())
+    RetType = CGM.getASTContext().getLValueReferenceType(RetType);
+
+  return emitAbstract(CE->getBeginLoc(), CE->getAPValueResult(), RetType);
+}
+
 mlir::Attribute ConstantEmitter::tryEmitAbstractForMemory(const Expr *E,
                                                           QualType destType) {
   auto nonMemoryDestType = getNonMemoryType(CGM, destType);

clang/lib/CIR/CodeGen/CIRGenModule.h

@@ -314,6 +314,12 @@ class CIRGenModule : public CIRGenTypeCache {
                                      StringRef Name = ".str");
   unsigned StringLiteralCnt = 0;
 
+  unsigned CompoundLitaralCnt = 0;
+  /// Return the unique name for global compound literal
+  std::string createGlobalCompoundLiteralName() {
+    return (Twine(".compoundLiteral.") + Twine(CompoundLitaralCnt++)).str();
+  }
+
   /// Return the AST address space of constant literal, which is used to emit
   /// the constant literal as global variable in LLVM IR.
   /// Note: This is not necessarily the address space of the constant literal

clang/test/CIR/CodeGen/compound-literal.c

@@ -0,0 +1,29 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir-enable -emit-cir %s -o %t.cir
+// RUN: FileCheck --input-file=%t.cir %s -check-prefix=CIR
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir-enable -S -emit-llvm %s -o %t.ll
+// RUN: FileCheck --input-file=%t.ll %s -check-prefix=LLVM
+
+
+typedef struct {
+  int *arr;
+} S;
+
+S a = {
+  .arr = (int[]){}
+};
+
+// CIR: cir.global "private" internal @".compoundLiteral.0" = #cir.zero : !cir.array<!s32i x 0> {alignment = 4 : i64}
+// CIR: cir.global external @a = #cir.const_struct<{#cir.global_view<@".compoundLiteral.0"> : !cir.ptr<!s32i>}> : !ty_22S22
+
+// LLVM: @.compoundLiteral.0 = internal global [0 x i32] zeroinitializer
+// LLVM: @a = global %struct.S { ptr @.compoundLiteral.0 }
+
+S b = {
+  .arr = (int[]){1}
+};
+
+// CIR: cir.global "private" internal @".compoundLiteral.1" = #cir.const_array<[#cir.int<1> : !s32i]> : !cir.array<!s32i x 1> {alignment = 4 : i64}
+// CIR: cir.global external @b = #cir.const_struct<{#cir.global_view<@".compoundLiteral.1"> : !cir.ptr<!s32i>}> : !ty_22S22
+
+// LLVM: @.compoundLiteral.1 = internal global [1 x i32] [i32 1]
+// LLVM: @b = global %struct.S { ptr @.compoundLiteral.1 }