[clang] [clang][bytecode] Reject uninitialized bases in builtin_bit_cast (PR #194625)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Timm Baeder (tbaederr)

<details>
<summary>Changes</summary>

Like the current interpreter does. Also use the bytecode interpreter in the test in SemaCXX/.

---
Full diff: https://github.com/llvm/llvm-project/pull/194625.diff


2 Files Affected:

- (modified) clang/lib/AST/ByteCode/InterpBuiltinBitCast.cpp (+3) 
- (modified) clang/test/SemaCXX/constexpr-builtin-bit-cast.cpp (+9) 


``````````diff
diff --git a/clang/lib/AST/ByteCode/InterpBuiltinBitCast.cpp b/clang/lib/AST/ByteCode/InterpBuiltinBitCast.cpp
index e48b0dc8e6a3e..5f90b419f1bfb 100644
--- a/clang/lib/AST/ByteCode/InterpBuiltinBitCast.cpp
+++ b/clang/lib/AST/ByteCode/InterpBuiltinBitCast.cpp
@@ -154,6 +154,9 @@ static Result enumerateData(const Pointer &P, const Context &Ctx, Bits Offset,
     }
     for (const Record::Base &B : R->bases()) {
       Pointer Elem = P.atField(B.Offset);
+      if (!Initialize && !Elem.isInitialized())
+        return Result::Failure;
+
       CharUnits ByteOffset =
           Layout.getBaseClassOffset(cast<CXXRecordDecl>(B.Decl));
       Bits BitOffset = Offset + Bits(Ctx.getASTContext().toBits(ByteOffset));
diff --git a/clang/test/SemaCXX/constexpr-builtin-bit-cast.cpp b/clang/test/SemaCXX/constexpr-builtin-bit-cast.cpp
index 839de82744379..ea5333df0b469 100644
--- a/clang/test/SemaCXX/constexpr-builtin-bit-cast.cpp
+++ b/clang/test/SemaCXX/constexpr-builtin-bit-cast.cpp
@@ -2,6 +2,11 @@
 // RUN: %clang_cc1 -verify -std=c++2a -fsyntax-only -triple x86_64-apple-macosx10.14.0 %s -fno-signed-char
 // RUN: %clang_cc1 -verify -std=c++2a -fsyntax-only -triple aarch64_be-linux-gnu %s
 
+// RUN: %clang_cc1 -verify -std=c++2a -fsyntax-only -triple x86_64-apple-macosx10.14.0 %s -fexperimental-new-constant-interpreter -DBYTECODE
+// RUN: %clang_cc1 -verify -std=c++2a -fsyntax-only -triple x86_64-apple-macosx10.14.0 %s -fno-signed-char -fexperimental-new-constant-interpreter -DBYTECODE
+// RUN: %clang_cc1 -verify -std=c++2a -fsyntax-only -triple aarch64_be-linux-gnu %s -fexperimental-new-constant-interpreter -DBYTECODE
+
+
 #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 #  define LITTLE_END 1
 #elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
@@ -132,6 +137,9 @@ void test_partially_initialized() {
   static_assert(fine.x == 1 && fine.y == 5);
 }
 
+/// This works in the bytecode interpreter and is tested
+/// in test/AST/ByteCode/builtin-bit-cast-bitfields.cpp
+#ifndef BYTECODE
 void no_bitfields() {
   // FIXME!
   struct S {
@@ -147,6 +155,7 @@ void no_bitfields() {
   // expected-note at +1 {{constexpr bit_cast involving bit-field is not yet supported}}
   constexpr G g = __builtin_bit_cast(G, s);
 }
+#endif
 
 void array_members() {
   struct S {

``````````

</details>


https://github.com/llvm/llvm-project/pull/194625