[clang] [Clang] Skip type-aware operator delete resolution for incomplete pointee types (PR #213455)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Ankit Kumar Tiwari (ankit-cybertron)

<details>
<summary>Changes</summary>

This PR adds a completeness check in `Sema::ActOnCXXDelete` so type-aware operator delete lookup is skipped when the pointee type is incomplete. 

Added a test covering C++17/23 (warn) and C++26 (error).

Fixes #<!-- -->212675


---
Full diff: https://github.com/llvm/llvm-project/pull/213455.diff


2 Files Affected:

- (modified) clang/lib/Sema/SemaExprCXX.cpp (+7-3) 
- (added) clang/test/SemaCXX/type-aware-delete-incomplete-type.cpp (+30) 


``````````diff
diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index 538604aa2e64b..08938291987ef 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -4149,9 +4149,14 @@ Sema::ActOnCXXDelete(SourceLocation StartLoc, bool UseGlobal,
     DeclarationName DeleteName = Context.DeclarationNames.getCXXOperatorName(
                                       ArrayForm ? OO_Array_Delete : OO_Delete);
 
+    bool IsComplete = isCompleteType(StartLoc, Pointee);
+    TypeAwareAllocationMode PassTypeIdentity =
+        IsComplete ? ShouldUseTypeAwareOperatorNewOrDelete()
+                   : TypeAwareAllocationMode::No;
+
     if (PointeeRD) {
       ImplicitDeallocationParameters IDP = {
-          Pointee, ShouldUseTypeAwareOperatorNewOrDelete(),
+          Pointee, PassTypeIdentity,
           AlignedAllocationMode::No, SizedDeallocationMode::No};
       if (!UseGlobal &&
           FindDeallocationFunction(StartLoc, PointeeRD, DeleteName,
@@ -4199,7 +4204,6 @@ Sema::ActOnCXXDelete(SourceLocation StartLoc, bool UseGlobal,
         return ExprError();
       }
 
-      bool IsComplete = isCompleteType(StartLoc, Pointee);
       bool CanProvideSize =
           IsComplete && (!ArrayForm || UsualArrayDeleteWantsSize ||
                          Pointee.isDestructedType());
@@ -4207,7 +4211,7 @@ Sema::ActOnCXXDelete(SourceLocation StartLoc, bool UseGlobal,
 
       // Look for a global declaration.
       ImplicitDeallocationParameters IDP = {
-          Pointee, ShouldUseTypeAwareOperatorNewOrDelete(),
+          Pointee, PassTypeIdentity,
           alignedAllocationModeFromBool(Overaligned),
           sizedDeallocationModeFromBool(CanProvideSize)};
       OperatorDelete = FindUsualDeallocationFunction(StartLoc, IDP, DeleteName);
diff --git a/clang/test/SemaCXX/type-aware-delete-incomplete-type.cpp b/clang/test/SemaCXX/type-aware-delete-incomplete-type.cpp
new file mode 100644
index 0000000000000..2eb74beaec8d0
--- /dev/null
+++ b/clang/test/SemaCXX/type-aware-delete-incomplete-type.cpp
@@ -0,0 +1,30 @@
+// RUN: %clang_cc1 -std=c++17 -fsyntax-only -verify=warn %s
+// RUN: %clang_cc1 -std=c++23 -fsyntax-only -verify=warn %s
+// RUN: %clang_cc1 -std=c++26 -fsyntax-only -verify=err %s
+// RUN: %clang_cc1 -std=c++17 -emit-llvm -o - %s | FileCheck %s
+
+class Foo; // warn-note {{forward declaration of 'Foo'}} \
+           // err-note {{forward declaration of 'Foo'}}
+
+typedef __SIZE_TYPE__ size_t;
+
+namespace std {
+  enum class align_val_t : size_t {};
+  template <class T> struct type_identity {
+    typedef T type;
+  };
+}
+
+template <class T>
+void operator delete(std::type_identity<T>, void *, size_t, std::align_val_t); // warn-warning {{type aware allocators are a Clang extension}} \
+                                                                                 // err-warning {{type aware allocators are a Clang extension}}
+
+void f(Foo *o) {
+  delete o;
+  // warn-warning at -1 {{deleting pointer to incomplete type 'Foo' is incompatible with C++2c and may cause undefined behavior}}
+  // err-error at -2 {{cannot delete pointer to incomplete type 'Foo'}}
+}
+
+// CHECK-LABEL: define {{.*}} @_Z1fP3Foo
+// CHECK-NOT: call {{.*}} @{{.*}}operator delete{{.*}}type_identity
+// CHECK: call void @_ZdlPv
\ No newline at end of file

``````````

</details>


https://github.com/llvm/llvm-project/pull/213455