[Clang] [Sema] Diagnose unknown std::initializer_list layout in SemaInit (#95580)

This checks if the layout of `std::initializer_list` is something Clang
can handle much earlier and deduplicates the checks in
CodeGen/CGExprAgg.cpp and AST/ExprConstant.cpp

Also now diagnose `union initializer_list` (Fixes #95495), bit-field for
the size (Fixes a crash that would happen during codegen if it were
unnamed), base classes (that wouldn't be initialized) and polymorphic
classes (whose vtable pointer wouldn't be initialized).

1 files changed, 18 insertions, 26 deletions

diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
index 0c87558..c3c10e7 100644
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -426,53 +426,45 @@ AggExprEmitter::VisitCXXStdInitializerListExpr(CXXStdInitializerListExpr *E) {
       Ctx.getAsConstantArrayType(E->getSubExpr()->getType());
   assert(ArrayType && "std::initializer_list constructed from non-array");
 
-  // FIXME: Perform the checks on the field types in SemaInit.
   RecordDecl *Record = E->getType()->castAs<RecordType>()->getDecl();
   RecordDecl::field_iterator Field = Record->field_begin();
-  if (Field == Record->field_end()) {
-    CGF.ErrorUnsupported(E, "weird std::initializer_list");
-    return;
-  }
+  assert(Field != Record->field_end() &&
+         Ctx.hasSameType(Field->getType()->getPointeeType(),
+                         ArrayType->getElementType()) &&
+         "Expected std::initializer_list first field to be const E *");
 
   // Start pointer.
-  if (!Field->getType()->isPointerType() ||
-      !Ctx.hasSameType(Field->getType()->getPointeeType(),
-                       ArrayType->getElementType())) {
-    CGF.ErrorUnsupported(E, "weird std::initializer_list");
-    return;
-  }
-
   AggValueSlot Dest = EnsureSlot(E->getType());
   LValue DestLV = CGF.MakeAddrLValue(Dest.getAddress(), E->getType());
   LValue Start = CGF.EmitLValueForFieldInitialization(DestLV, *Field);
   llvm::Value *ArrayStart = ArrayPtr.emitRawPointer(CGF);
   CGF.EmitStoreThroughLValue(RValue::get(ArrayStart), Start);
   ++Field;
-
-  if (Field == Record->field_end()) {
-    CGF.ErrorUnsupported(E, "weird std::initializer_list");
-    return;
-  }
+  assert(Field != Record->field_end() &&
+         "Expected std::initializer_list to have two fields");
 
   llvm::Value *Size = Builder.getInt(ArrayType->getSize());
   LValue EndOrLength = CGF.EmitLValueForFieldInitialization(DestLV, *Field);
-  if (Field->getType()->isPointerType() &&
-      Ctx.hasSameType(Field->getType()->getPointeeType(),
-                      ArrayType->getElementType())) {
+  if (Ctx.hasSameType(Field->getType(), Ctx.getSizeType())) {
+    // Length.
+    CGF.EmitStoreThroughLValue(RValue::get(Size), EndOrLength);
+
+  } else {
     // End pointer.
+    assert(Field->getType()->isPointerType() &&
+           Ctx.hasSameType(Field->getType()->getPointeeType(),
+                           ArrayType->getElementType()) &&
+           "Expected std::initializer_list second field to be const E *");
     llvm::Value *Zero = llvm::ConstantInt::get(CGF.PtrDiffTy, 0);
     llvm::Value *IdxEnd[] = { Zero, Size };
     llvm::Value *ArrayEnd = Builder.CreateInBoundsGEP(
         ArrayPtr.getElementType(), ArrayPtr.emitRawPointer(CGF), IdxEnd,
         "arrayend");
     CGF.EmitStoreThroughLValue(RValue::get(ArrayEnd), EndOrLength);
-  } else if (Ctx.hasSameType(Field->getType(), Ctx.getSizeType())) {
-    // Length.
-    CGF.EmitStoreThroughLValue(RValue::get(Size), EndOrLength);
-  } else {
-    CGF.ErrorUnsupported(E, "weird std::initializer_list");
-    return;
   }
+
+  assert(++Field == Record->field_end() &&
+         "Expected std::initializer_list to only have two fields");
 }
 
 /// Determine if E is a trivial array filler, that is, one that is