[CodeGen] Add support for IncompleteArrayType in Obj-C ivars.

[vsapsai]

Summary

Fixes an assertion failure when ivar is a struct containing incomplete
array. Also completes support for direct flexible array members.

rdar://problem/21054495

[vsapsai]

This patch depends on sema change https://reviews.llvm.org/D38773

[vsapsai]

To save reviewers some time. Incomplete array type is not the same as for zero-sized array, it is c"^c\00" while for zero-sized array it is c"[0c]\00". Don't know if it matters, I haven't found any difference in behaviour. Though maybe I wasn't looking in the right place.

[rjmccall]

clang/lib/CodeGen/CGObjCMac.cpp

5095 ↗

(On Diff #118510)

You can't just use isa<> here; there can be typedefs of incomplete array type.

[vsapsai]

clang/lib/CodeGen/CGObjCMac.cpp

5095 ↗

(On Diff #118510)

Thanks for catching it.

[vsapsai]

• Address rjmccall review comment about isa<>.

Decided to keep in test only cases with typedefs because test coverage is the
same and there is less similar code.

[vsapsai]

• Resubmit my last change without files from underlying branch.

[rjmccall]

clang/lib/CodeGen/CGObjCMac.cpp

5095 ↗

(On Diff #118510)

Oh, and C allows you to have incomplete arrays of array type, e.g. int x[][4];

[vsapsai]

clang/lib/CodeGen/CGObjCMac.cpp

5095 ↗

(On Diff #118510)

Right, thanks. I've checked only that int x[][]; isn't accepted but forgot about mixing different arrays.

[vsapsai]

• Address rjmccall review comment about nested arrays.

[rjmccall]

Thanks, LGTM.

cfe/trunk/lib/CodeGen/CGObjCMac.cpp

 
 /// Collect layout information for the given fields into IvarsInfo.
 void IvarLayoutBuilder::visitField(const FieldDecl *field,
                                    CharUnits fieldOffset) {
   QualType fieldType = field->getType();
 
   // Drill down into arrays.
   uint64_t numElts = 1;
+  if (auto arrayType = CGM.getContext().getAsIncompleteArrayType(fieldType)) {
+    numElts = 0;
+    fieldType = arrayType->getElementType();
+  }
+  // Unlike incomplete arrays, constant arrays can be nested.
   while (auto arrayType = CGM.getContext().getAsConstantArrayType(fieldType)) {
     numElts *= arrayType->getSize().getZExtValue();
     fieldType = arrayType->getElementType();
   }
 
   assert(!fieldType->isArrayType() && "ivar of non-constant array type?");
 
   // If we ended up with a zero-sized array, we've done what we can do within

cfe/trunk/test/CodeGenObjC/ivar-layout-flexible-array.m

+// RUN: %clang_cc1 -triple x86_64-apple-darwin -Wno-objc-root-class -fobjc-arc -emit-llvm -o - %s | FileCheck %s
+
+// rdar://problem/21054495
+@interface FlexibleArrayMember {
+  char flexible_array[][4][2];
+}
+@end
+@implementation FlexibleArrayMember
+@end
+// CHECK: @OBJC_METH_VAR_NAME_{{.*}} = private unnamed_addr constant {{.*}} c"flexible_array\00"
+// CHECK-NEXT: @OBJC_METH_VAR_TYPE_{{.*}} = private unnamed_addr constant {{.*}} c"^[4[2c]]\00"
+
+
+typedef char FlexibleArray[];
+
+struct Packet {
+  int size;
+  FlexibleArray data;
+};
+
+@interface VariableSizeIvar {
+  struct Packet flexible_struct;
+}
+@end
+@implementation VariableSizeIvar
+@end
+// CHECK: @OBJC_METH_VAR_NAME_{{.*}} = private unnamed_addr constant {{.*}} c"flexible_struct\00"
+// CHECK-NEXT: @OBJC_METH_VAR_TYPE_{{.*}} = private unnamed_addr constant {{.*}} c"{Packet=\22size\22i\22data\22[0c]}\00"