[clang] [clang][bytecode] Don't implicitly begin union member lifetime... (PR #192212)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Timm Baeder (tbaederr)

<details>
<summary>Changes</summary>

... on assignment operator calls if the LHS type does not have a non-deleted trivial default constructor.

---
Full diff: https://github.com/llvm/llvm-project/pull/192212.diff


2 Files Affected:

- (modified) clang/lib/AST/ByteCode/Compiler.cpp (+5-1) 
- (modified) clang/test/AST/ByteCode/unions.cpp (+22) 


``````````diff
diff --git a/clang/lib/AST/ByteCode/Compiler.cpp b/clang/lib/AST/ByteCode/Compiler.cpp
index 59510612d9617..a0d52c6580d74 100644
--- a/clang/lib/AST/ByteCode/Compiler.cpp
+++ b/clang/lib/AST/ByteCode/Compiler.cpp
@@ -5601,6 +5601,7 @@ bool Compiler<Emitter>::VisitCallExpr(const CallExpr *E) {
   SmallVector<const Expr *, 8> Args(ArrayRef(E->getArgs(), E->getNumArgs()));
 
   bool IsAssignmentOperatorCall = false;
+  bool ActivateLHS = false;
   if (const auto *OCE = dyn_cast<CXXOperatorCallExpr>(E);
       OCE && OCE->isAssignmentOp()) {
     // Just like with regular assignments, we need to special-case assignment
@@ -5609,6 +5610,9 @@ bool Compiler<Emitter>::VisitCallExpr(const CallExpr *E) {
     assert(Args.size() == 2);
     IsAssignmentOperatorCall = true;
     std::reverse(Args.begin(), Args.end());
+    const CXXRecordDecl *LHSRecord = Args[0]->getType()->getAsCXXRecordDecl();
+    assert(LHSRecord);
+    ActivateLHS = LHSRecord->hasTrivialDefaultConstructor();
   }
   // Calling a static operator will still
   // pass the instance, but we don't need it.
@@ -5684,7 +5688,7 @@ bool Compiler<Emitter>::VisitCallExpr(const CallExpr *E) {
       return false;
   }
 
-  if (!this->visitCallArgs(Args, FuncDecl, IsAssignmentOperatorCall,
+  if (!this->visitCallArgs(Args, FuncDecl, ActivateLHS,
                            isa<CXXOperatorCallExpr>(E)))
     return false;
 
diff --git a/clang/test/AST/ByteCode/unions.cpp b/clang/test/AST/ByteCode/unions.cpp
index 2123a932fce10..d005b45795931 100644
--- a/clang/test/AST/ByteCode/unions.cpp
+++ b/clang/test/AST/ByteCode/unions.cpp
@@ -1007,4 +1007,26 @@ namespace NonTrivialUnionCtor {
   static_assert(j()); // both-error {{not an integral constant expression}} \
                       // both-note {{in call to}}
 }
+
+/// u.a should not implicitly get activated when assigning to it, since A
+/// does not have a non-deleted trivial default constructor.
+namespace NoTrivialCtor {
+  struct A {
+   int i;
+   constexpr A() : i(0) {}
+   constexpr A(int i) : i(i) {}
+  };
+
+  constexpr auto test() {
+   union U {
+    int i;
+    A a;
+   } u{.i = 0};
+
+   u.a = {123};
+   return u.a.i;
+  }
+
+ constexpr auto r = test();
+}
 #endif

``````````

</details>


https://github.com/llvm/llvm-project/pull/192212