Reapply "[Clang][Sema] placement new initializes typedef array with correct size (#83124)" (#89036)

When in-place new-ing a local variable of an array of trivial type, the
generated code calls 'memset' with the correct size of the array,
earlier it was generating size (squared of the typedef array + size).

The cause: typedef TYPE TArray[8]; TArray x; The type of declarator is
Tarray[8] and in SemaExprCXX.cpp::BuildCXXNew we check if it's of
typedef and of constant size then we get the original type and it works
fine for non-dependent cases.
But in case of template we do TreeTransform.h:TransformCXXNEWExpr and
there we again check the allocated type which is TArray[8] and it stays
that way, so ArraySize=(Tarray[8] type, alloc Tarray[8*type]) so the
squared size allocation.

ArraySize gets calculated earlier in TreeTransform.h so that
if(!ArraySize) condition was failing.
fix: I changed that condition to if(ArraySize).
fixes #41441

---------

Co-authored-by: erichkeane <[email protected]>

Author: mahtohappy

clang/docs/ReleaseNotes.rst

@@ -557,6 +557,7 @@ Bug Fixes to C++ Support
 - Fix a crash in requires expression with templated base class member function. Fixes (#GH84020).
 - Fix a crash caused by defined struct in a type alias template when the structure
   has fields with dependent type. Fixes (#GH75221).
+- Fix placement new initializes typedef array with correct size. Fixes (#GH41441).
 - Fix the Itanium mangling of lambdas defined in a member of a local class (#GH88906)
 - Fixed a crash when trying to evaluate a user-defined ``static_assert`` message whose ``size()``
   function returns a large or negative value. Fixes (#GH89407).

clang/lib/Sema/TreeTransform.h

@@ -12943,6 +12943,19 @@ TreeTransform<Derived>::TransformCXXNewExpr(CXXNewExpr *E) {
     ArraySize = NewArraySize.get();
   }
 
+  // Per C++0x [expr.new]p5, the type being constructed may be a
+  // typedef of an array type.
+  QualType AllocType = AllocTypeInfo->getType();
+  if (ArraySize && E->isTypeDependent()) {
+    if (const ConstantArrayType *Array =
+            SemaRef.Context.getAsConstantArrayType(AllocType)) {
+      ArraySize = IntegerLiteral::Create(SemaRef.Context, Array->getSize(),
+                                         SemaRef.Context.getSizeType(),
+                                         E->getBeginLoc());
+      AllocType = Array->getElementType();
+    }
+  }
+
   // Transform the placement arguments (if any).
   bool ArgumentChanged = false;
   SmallVector<Expr*, 8> PlacementArgs;
@@ -13004,7 +13017,6 @@ TreeTransform<Derived>::TransformCXXNewExpr(CXXNewExpr *E) {
     return E;
   }
 
-  QualType AllocType = AllocTypeInfo->getType();
   if (!ArraySize) {
     // If no array size was specified, but the new expression was
     // instantiated with an array type (e.g., "new T" where T is

clang/lib/Serialization/ASTWriter.cpp

@@ -5097,7 +5097,7 @@ void ASTWriter::WriteSpecialDeclRecords(Sema &SemaRef) {
       DeclsToCheckForDeferredDiags.push_back(getDeclID(D));
   if (!DeclsToCheckForDeferredDiags.empty())
     Stream.EmitRecord(DECLS_TO_CHECK_FOR_DEFERRED_DIAGS,
-        DeclsToCheckForDeferredDiags);
+                      DeclsToCheckForDeferredDiags);
 
   // Write the record containing CUDA-specific declaration references.
   RecordData CUDASpecialDeclRefs;

clang/test/SemaCXX/PR41441.cpp

@@ -0,0 +1,32 @@
+// RUN: %clang --target=x86_64-pc-linux -S -fno-discard-value-names -emit-llvm -o - %s | FileCheck %s
+
+namespace std {
+  using size_t = decltype(sizeof(int));
+};
+void* operator new[](std::size_t, void*) noexcept;
+
+// CHECK: call void @llvm.memset.p0.i64(ptr align 1 %x, i8 0, i64 8, i1 false)
+// CHECK: call void @llvm.memset.p0.i64(ptr align 16 %x, i8 0, i64 32, i1 false)
+template <typename TYPE>
+void f()
+{
+    typedef TYPE TArray[8];
+
+    TArray x;
+    new(&x) TArray();
+}
+
+template <typename T>
+void f1() {
+  int (*x)[1] = new int[1][1];
+}
+template void f1<char>();
+void f2() {
+  int (*x)[1] = new int[1][1];
+}
+
+int main()
+{
+    f<char>();
+    f<int>();
+}