[ObjC] Fix offsets following [[no_unique_address]] for @encode()

[BertalanD]

Commit 46ca880 made @encode skip fields that are made zero-sized by [[no_unique_address]]. When iterating the fields, the index which is passed to getFieldOffset failed to be incremented for those due to the use of an early continue, so subsequent fields reported an incorrect offset. This caused an assertion to be triggered in getObjCEncodingForStructureImpl.

Fixes #71250

[llvmbot]

@llvm/pr-subscribers-clang

Author: Daniel Bertalan (BertalanD)

Changes

Commit 46ca880 made @<!-- -->encode skip fields that are made zero-sized by [[no_unique_address]]. When iterating the fields, the index which is passed to getFieldOffset failed to be incremented for those due to the use of an early continue, so subsequent fields reported an incorrect offset. This caused an assertion to be triggered in getObjCEncodingForStructureImpl.

Fixes #71250

---

Full diff: https://github.com/llvm/llvm-project/pull/71321.diff

2 Files Affected:

• (modified) clang/lib/AST/ASTContext.cpp (+1-3)
• (modified) clang/test/CodeGenObjCXX/encode.mm (+14)

diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index da90136752210b6..60146e9901bc44d 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -8535,14 +8535,12 @@ void ASTContext::getObjCEncodingForStructureImpl(RecordDecl *RDecl,
     }
   }
 
-  unsigned i = 0;
   for (FieldDecl *Field : RDecl->fields()) {
     if (!Field->isZeroLengthBitField(*this) && Field->isZeroSize(*this))
       continue;
-    uint64_t offs = layout.getFieldOffset(i);
+    uint64_t offs = layout.getFieldOffset(Field->getFieldIndex());
     FieldOrBaseOffsets.insert(FieldOrBaseOffsets.upper_bound(offs),
                               std::make_pair(offs, Field));
-    ++i;
   }
 
   if (CXXRec && includeVBases) {
diff --git a/clang/test/CodeGenObjCXX/encode.mm b/clang/test/CodeGenObjCXX/encode.mm
index f382e7f23d77335..cad70e379c386bf 100644
--- a/clang/test/CodeGenObjCXX/encode.mm
+++ b/clang/test/CodeGenObjCXX/encode.mm
@@ -339,3 +339,17 @@ @implementation N
 const char *inner0 = @encode(Outer0<int>::Inner0 *);
 const char *inner1 = @encode(Outer0<int>::Inner1<float> *);
 }
+
+#if __cplusplus >= 202002L
+namespace GH71250 {
+  struct Empty {};
+  struct S {
+    [[no_unique_address]] Empty a;
+    long b;
+    long c;
+  };
+
+  // CHECKCXX20: @_ZN7GH712501sE =  constant [7 x i8] c"{S=qq}\00", align 1
+  extern const char s[] = @encode(S);
+}
+#endif

[rjmccall]

LGTM

[nico]

lg2m