[clang] af189c8 - Fix constant evaluation of zero-initialization of a union whose first

[Richard Smith via cfe-commits]

Author: Richard Smith
Date: 2020-10-22T17:03:59-07:00
New Revision: af189c8ab113668434eae5c71f174613a9e64625

URL: https://github.com/llvm/llvm-project/commit/af189c8ab113668434eae5c71f174613a9e64625
DIFF: https://github.com/llvm/llvm-project/commit/af189c8ab113668434eae5c71f174613a9e64625.diff

LOG: Fix constant evaluation of zero-initialization of a union whose first
FieldDecl is an unamed bitfield.

Unnamed bitfields aren't non-static data member, so such a bitfield
isn't actually the first non-static data member.

Added: 
    

Modified: 
    clang/lib/AST/ExprConstant.cpp
    clang/test/SemaCXX/constant-expression-cxx11.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index e978a190a195..c6fc02a6fe91 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -9630,6 +9630,8 @@ bool RecordExprEvaluator::ZeroInitialization(const Expr *E, QualType T) {
     // C++11 [dcl.init]p5: If T is a (possibly cv-qualified) union type, the
     // object's first non-static named data member is zero-initialized
     RecordDecl::field_iterator I = RD->field_begin();
+    while (I != RD->field_end() && (*I)->isUnnamedBitfield())
+      ++I;
     if (I == RD->field_end()) {
       Result = APValue((const FieldDecl*)nullptr);
       return true;

diff  --git a/clang/test/SemaCXX/constant-expression-cxx11.cpp b/clang/test/SemaCXX/constant-expression-cxx11.cpp
index 0d67b747a0f4..7d51a48eac42 100644
--- a/clang/test/SemaCXX/constant-expression-cxx11.cpp
+++ b/clang/test/SemaCXX/constant-expression-cxx11.cpp
@@ -2021,6 +2021,14 @@ namespace Bitfields {
     const HasUnnamedBitfield oneZero{1, 0};
     int b = 1 / oneZero.b; // expected-warning {{division by zero is undefined}}
   }
+
+  union UnionWithUnnamedBitfield {
+    int : 3;
+    int n;
+  };
+  static_assert(UnionWithUnnamedBitfield().n == 0, "");
+  static_assert(UnionWithUnnamedBitfield{}.n == 0, "");
+  static_assert(UnionWithUnnamedBitfield{1}.n == 1, "");
 }
 
 namespace ZeroSizeTypes {