--- tools/clang/tools/include-what-you-use/iwyu_ast_util.cc.orig	2020-03-23 14:03:01.060932783 -0700
+++ tools/clang/tools/include-what-you-use/iwyu_ast_util.cc	2020-03-23 14:04:37.056235116 -0700
@@ -47,6 +47,7 @@
 class FileEntry;
 }  // namespace clang
 
+using clang::ASTContext;
 using clang::BlockPointerType;
 using clang::CXXConstructExpr;
 using clang::CXXConstructorDecl;
@@ -78,6 +79,7 @@
 using clang::FullSourceLoc;
 using clang::FunctionDecl;
 using clang::FunctionType;
+using clang::IdentifierInfo;
 using clang::ImplicitCastExpr;
 using clang::InjectedClassNameType;
 using clang::LValueReferenceType;
@@ -929,13 +931,81 @@
       !StartsWith(decl_name, "operator delete"))
     return false;
 
-  // Placement-new/delete has 2 args, second is void*.  The only other
-  // 2-arg overloads of new/delete in <new> take a const nothrow_t&.
-  if (decl->getNumParams() == 2 &&
-      !decl->getParamDecl(1)->getType().isConstQualified())
-    return false;
-
-  return true;
+  // The following variants of operator new[1] are implicitly defined in every
+  // translation unit and should not require including <new>.
+  //
+  // void* operator new  ( std::size_t count );
+  // void* operator new[]( std::size_t count );
+  // void* operator new  ( std::size_t count, std::align_val_t al ); (since C++17)
+  // void* operator new[]( std::size_t count, std::align_val_t al ); (since C++17)
+  //  
+  // Likewise, the following variants of operator delete[2] are implicitly
+  // defined in every translation unit and should not require including <new>.
+  //
+  // void operator delete  ( void* ptr ) throw(); (until C++11)
+  // void operator delete  ( void* ptr ) noexcept; (since C++11)
+  // void operator delete[]( void* ptr ) throw(); (until C++11)
+  // void operator delete[]( void* ptr ) noexcept; (since C++11)
+  // void operator delete  ( void* ptr, std::align_val_t al ) noexcept; (since C++17)
+  // void operator delete[]( void* ptr, std::align_val_t al ) noexcept; (since C++17)
+  // void operator delete  ( void* ptr, std::size_t sz ) noexcept; (since C++14)
+  // void operator delete[]( void* ptr, std::size_t sz ) noexcept; (since C++14)
+  // void operator delete  ( void* ptr, std::size_t sz,
+  //                         std::align_val_t al ) noexcept; (since C++17)
+  // void operator delete[]( void* ptr, std::size_t sz,
+  //                         std::align_val_t al ) noexcept; (since C++17)
+  // void operator delete  ( void* ptr, const std::nothrow_t& tag ) throw(); (until C++11)
+  // void operator delete  ( void* ptr, const std::nothrow_t& tag ) noexcept; (since C++11)
+  // void operator delete[]( void* ptr, const std::nothrow_t& tag ) throw(); (until C++11)
+  // void operator delete[]( void* ptr, const std::nothrow_t& tag ) noexcept; (since C++11)
+  //
+  // The below code attempts to return true for these variants while returning
+  // false for all others. FunctionDecl::isReplaceableGlobalAllocationFunction
+  // comes very very close, but returns true for nothrow new, which is not
+  // implicitly defined.
+  //
+  // 1. https://en.cppreference.com/w/cpp/memory/new/operator_new
+  // 2. https://en.cppreference.com/w/cpp/memory/new/operator_delete
+  switch (decl->getNumParams()) {
+    case 1:
+      // All 1-arg variants are implicitly declared.
+      return true;
+    case 2: {
+      // Amongst 2-arg variants, aligned (C++17) new/delete, sized delete (C++14), and
+      // nothrow delete are implicitly declared.
+      ASTContext& ctx = decl->getASTContext();
+      QualType t = decl->getParamDecl(1)->getType();
+      if (t->isAlignValT() ||                     // aligned new/delete
+          ctx.hasSameType(t, ctx.getSizeType()))  // sized delete
+        return true;
+      // We have to work a bit harder to figure out if it's a nothrow delete.
+      //
+      // This cribs from FunctionDecl::isReplaceableGlobalAllocationFunction.
+      if (StartsWith(decl_name, "operator delete") && t->isReferenceType()) {
+        t = t->getPointeeType();
+        if (t.isConstQualified()) {
+          const CXXRecordDecl* recordDecl = t->getAsCXXRecordDecl();
+          if (recordDecl) {
+            const IdentifierInfo* iInfo = recordDecl->getIdentifier();
+            if (iInfo && iInfo->isStr("nothrow_t") && recordDecl->isInStdNamespace())
+              return true;
+          }
+        }
+      }
+      return false;
+    }
+    case 3: {
+      // Amongst 3-arg variants, only sized aligned delete (C++17) is implicitly
+      // declared.
+      ASTContext& ctx = decl->getASTContext();
+      QualType t = decl->getParamDecl(1)->getType();
+      return ctx.hasSameType(t, ctx.getSizeType()) &&
+             decl->getParamDecl(2)->getType()->isAlignValT();
+    }
+    default:
+      return false;
+    return true;
+  }
 }
 
 bool IsFriendDecl(const Decl* decl) {
@@ -1082,7 +1152,7 @@
 
 bool IsBuiltinFunction(const clang::NamedDecl* decl,
                        const std::string& symbol_name) {
-  if (const clang::IdentifierInfo* iden = decl->getIdentifier()) {
+  if (const IdentifierInfo* iden = decl->getIdentifier()) {
     return iden->getBuiltinID() != 0 &&
            !clang::Builtin::Context::isBuiltinFunc(symbol_name.c_str());
   }