[clang] Be careful when choosing "fast path" for initialization with #embed (#99023)

When #embed appears in an initializer list, we may choose a "fast path"
if the target declaration is a char array. We simply initialize it with
string literal that contains embedded data. However we need to be
careful when checking that we actually can use this "fast path" since
char array may be nested in a struct.

Author: Fznamznon

clang/lib/Sema/SemaInit.cpp

@@ -1993,9 +1993,18 @@ static bool checkDestructorReference(QualType ElementType, SourceLocation Loc,
   return SemaRef.DiagnoseUseOfDecl(Destructor, Loc);
 }
 
-static bool canInitializeArrayWithEmbedDataString(ArrayRef<Expr *> ExprList,
-                                                  QualType InitType,
-                                                  ASTContext &Context) {
+static bool
+canInitializeArrayWithEmbedDataString(ArrayRef<Expr *> ExprList,
+                                      const InitializedEntity &Entity,
+                                      ASTContext &Context) {
+  QualType InitType = Entity.getType();
+  const InitializedEntity *Parent = &Entity;
+
+  while (Parent) {
+    InitType = Parent->getType();
+    Parent = Parent->getParent();
+  }
+
   // Only one initializer, it's an embed and the types match;
   EmbedExpr *EE =
       ExprList.size() == 1
@@ -2034,7 +2043,7 @@ void InitListChecker::CheckArrayType(const InitializedEntity &Entity,
     }
   }
 
-  if (canInitializeArrayWithEmbedDataString(IList->inits(), DeclType,
+  if (canInitializeArrayWithEmbedDataString(IList->inits(), Entity,
                                             SemaRef.Context)) {
     EmbedExpr *Embed = cast<EmbedExpr>(IList->inits()[0]);
     IList->setInit(0, Embed->getDataStringLiteral());

clang/test/Preprocessor/embed_codegen.cpp

@@ -3,6 +3,7 @@
 // CHECK: @__const._Z3fooi.ca = private unnamed_addr constant [3 x i32] [i32 0, i32 106, i32 107], align 4
 // CHECK: @__const._Z3fooi.sc = private unnamed_addr constant %struct.S1 { i32 106, i32 107, i32 0 }, align 4
 // CHECK: @__const._Z3fooi.t = private unnamed_addr constant [3 x %struct.T] [%struct.T { [2 x i32] [i32 48, i32 49], %struct.S1 { i32 50, i32 51, i32 52 } }, %struct.T { [2 x i32] [i32 53, i32 54], %struct.S1 { i32 55, i32 56, i32 57 } }, %struct.T { [2 x i32] [i32 10, i32 0], %struct.S1 zeroinitializer }], align 16
+// CHECK: @__const._Z3fooi.W = private unnamed_addr constant %struct.Wrapper { i32 48, %struct.HasCharArray { [10 x i8] c"123456789\0A" } }, align 4
 void foo(int a) {
 // CHECK: %a.addr = alloca i32, align 4
 // CHECK: store i32 %a, ptr %a.addr, align 4
@@ -82,4 +83,11 @@ struct T tnonc[] = {
 #embed <jk.txt> prefix(,)
 };
 
+
+struct HasCharArray { unsigned char h[10]; };
+struct Wrapper { int a; struct HasCharArray d;  };
+constexpr struct Wrapper W = {
+#embed "numbers.txt"
+};
+
 }

clang/test/Preprocessor/embed_constexpr.cpp

@@ -96,3 +96,11 @@ struct ST {};
 ST<
 #embed <jk.txt> limit(1)
 > st;
+
+struct HasCharArray { unsigned char h[10]; };
+struct Wrapper { int a; struct HasCharArray d;  };
+constexpr struct Wrapper W = {
+#embed "numbers.txt"
+};
+
+static_assert(W.d.h[2] == '3');