[clang] [Clang][Sema] placement new initializes typedef array with correct size (PR #89036)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: None (mahtohappy)

<details>
<summary>Changes</summary>

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 https://github.com/llvm/llvm-project/issues/41441

---
Full diff: https://github.com/llvm/llvm-project/pull/89036.diff


3 Files Affected:

- (modified) clang/docs/ReleaseNotes.rst (+2) 
- (modified) clang/lib/Sema/TreeTransform.h (+13-1) 
- (added) clang/test/SemaCXX/PR41441.cpp (+23) 


``````````diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 96ad92b540b47f..636d76f1836759 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -534,6 +534,8 @@ Bug Fixes to C++ Support
   Fixes (#GH70604), (#GH79754), (#GH84163), (#GH84425), (#GH86054), (#GH86398), and (#GH86399).
 - Fix a crash when deducing ``auto`` from an invalid dereference (#GH88329).
 - Fix a crash in requires expression with templated base class member function. Fixes (#GH84020).
+- placement new initializes typedef array with correct size
+  (`#GH41441 <https://github.com/llvm/llvm-project/issues/41441>`_)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
index eb05783a6219dc..0c7fdb357235e1 100644
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -12864,6 +12864,19 @@ 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) {
+    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;
@@ -12925,7 +12938,6 @@ 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
diff --git a/clang/test/SemaCXX/PR41441.cpp b/clang/test/SemaCXX/PR41441.cpp
new file mode 100644
index 00000000000000..d0f2917e52f211
--- /dev/null
+++ b/clang/test/SemaCXX/PR41441.cpp
@@ -0,0 +1,23 @@
+// 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();
+}
+
+int main()
+{
+    f<char>();
+    f<int>();
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/89036