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

[via cfe-commits]

https://github.com/mahtohappy created https://github.com/llvm/llvm-project/pull/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 https://github.com/llvm/llvm-project/issues/41441

>From 56c2b4f70735a6ef3b80cb8461a88ea51f2d02d7 Mon Sep 17 00:00:00 2001
From: mahtohappy <Happy.Kumar at Windriver.com>
Date: Tue, 16 Apr 2024 17:48:45 +0530
Subject: [PATCH 1/3] [Clang][Sema] placement new initializes typedef array
 with correct size (#83124)

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
---
 clang/docs/ReleaseNotes.rst                   |  2 ++
 clang/lib/Sema/TreeTransform.h                | 14 ++++++++++++-
 .../instantiate-new-placement-size.cpp        | 20 +++++++++++++++++++
 3 files changed, 35 insertions(+), 1 deletion(-)
 create mode 100644 clang/test/SemaCXX/instantiate-new-placement-size.cpp

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/instantiate-new-placement-size.cpp b/clang/test/SemaCXX/instantiate-new-placement-size.cpp
new file mode 100644
index 00000000000000..7a29d3dee8491e
--- /dev/null
+++ b/clang/test/SemaCXX/instantiate-new-placement-size.cpp
@@ -0,0 +1,20 @@
+// RUN: %clang -S -fno-discard-value-names -emit-llvm -o - %s | FileCheck %s
+// Issue no: 41441
+#include <new>
+
+// 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>();
+}

>From bdd7f66e560f60d1f0027b04ad12989b2f786df3 Mon Sep 17 00:00:00 2001
From: mahtohappy <Happy.Kumar at Windriver.com>
Date: Wed, 17 Apr 2024 00:12:14 +0530
Subject: [PATCH 2/3] [Clang][Sema] placement new initializes typedef array
 with correct size (#88902)

Build Failure Fix
Fixes build failures due to #83124
---
 .../{instantiate-new-placement-size.cpp => PR41441.cpp}       | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
 rename clang/test/SemaCXX/{instantiate-new-placement-size.cpp => PR41441.cpp} (75%)

diff --git a/clang/test/SemaCXX/instantiate-new-placement-size.cpp b/clang/test/SemaCXX/PR41441.cpp
similarity index 75%
rename from clang/test/SemaCXX/instantiate-new-placement-size.cpp
rename to clang/test/SemaCXX/PR41441.cpp
index 7a29d3dee8491e..0b012b33fce343 100644
--- a/clang/test/SemaCXX/instantiate-new-placement-size.cpp
+++ b/clang/test/SemaCXX/PR41441.cpp
@@ -1,5 +1,5 @@
-// RUN: %clang -S -fno-discard-value-names -emit-llvm -o - %s | FileCheck %s
-// Issue no: 41441
+// RUN: %clang --target=x86_64-pc-linux -S -fno-discard-value-names -emit-llvm -o - %s | FileCheck %s
+
 #include <new>
 
 // CHECK: call void @llvm.memset.p0.i64(ptr align 1 %x, i8 0, i64 8, i1 false)

>From 71f00c3bf2b6f0047d51332843490de08c097490 Mon Sep 17 00:00:00 2001
From: erichkeane <ekeane at nvidia.com>
Date: Tue, 16 Apr 2024 12:12:25 -0700
Subject: [PATCH 3/3] Fix test from #83124 and #88902

This just replaces an '#include<new>' with a declaration of array
placement new.
---
 clang/test/SemaCXX/PR41441.cpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/clang/test/SemaCXX/PR41441.cpp b/clang/test/SemaCXX/PR41441.cpp
index 0b012b33fce343..d0f2917e52f211 100644
--- a/clang/test/SemaCXX/PR41441.cpp
+++ b/clang/test/SemaCXX/PR41441.cpp
@@ -1,6 +1,9 @@
 // RUN: %clang --target=x86_64-pc-linux -S -fno-discard-value-names -emit-llvm -o - %s | FileCheck %s
 
-#include <new>
+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)