diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -476,6 +476,7 @@
 // Key paths that are constant during parsing of options with the same key path prefix.
 defvar cplusplus = LangOpts<"CPlusPlus">;
 defvar cpp11 = LangOpts<"CPlusPlus11">;
+defvar cpp14 = LangOpts<"CPlusPlus14">;
 defvar cpp17 = LangOpts<"CPlusPlus17">;
 defvar cpp20 = LangOpts<"CPlusPlus20">;
 defvar c99 = LangOpts<"C99">;
@@ -2339,9 +2340,9 @@
   PosFlag<SetTrue>,
   NegFlag<SetFalse, [CC1Option], "Disable C++17 relaxed template template argument matching">>;
 defm sized_deallocation : BoolFOption<"sized-deallocation",
-  LangOpts<"SizedDeallocation">, DefaultFalse,
-  PosFlag<SetTrue, [CC1Option], "Enable C++14 sized global deallocation functions">,
-  NegFlag<SetFalse>>;
+  LangOpts<"SizedDeallocation">, Default<cpp14.KeyPath>,
+  PosFlag<SetTrue, [], "Enable C++14 sized global deallocation functions">,
+  NegFlag<SetFalse>, BothFlags<[CC1Option]>>;
 defm aligned_allocation : BoolFOption<"aligned-allocation",
   LangOpts<"AlignedAllocation">, Default<cpp17.KeyPath>,
   PosFlag<SetTrue, [], "Enable C++17 aligned allocation functions">,
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -6400,11 +6400,15 @@
       CmdArgs.push_back("-fno-relaxed-template-template-args");
   }
 
-  // -fsized-deallocation is off by default, as it is an ABI-breaking change for
-  // most platforms.
-  if (Args.hasFlag(options::OPT_fsized_deallocation,
-                   options::OPT_fno_sized_deallocation, false))
-    CmdArgs.push_back("-fsized-deallocation");
+  // -fsized-deallocation is on by default in C++14 onwards and otherwise off
+  // by default.
+  if (Arg *A = Args.getLastArg(options::OPT_fsized_deallocation,
+                               options::OPT_fno_sized_deallocation)) {
+    if (A->getOption().matches(options::OPT_fsized_deallocation))
+      CmdArgs.push_back("-fsized-deallocation");
+    else
+      CmdArgs.push_back("-fno-sized-deallocation");
+  }
 
   // -faligned-allocation is on by default in C++17 onwards and otherwise off
   // by default.
diff --git a/clang/test/AST/ast-dump-expr.cpp b/clang/test/AST/ast-dump-expr.cpp
--- a/clang/test/AST/ast-dump-expr.cpp
+++ b/clang/test/AST/ast-dump-expr.cpp
@@ -1,10 +1,10 @@
 // Test without serialization:
-// RUN: %clang_cc1 -triple x86_64-unknown-unknown -Wno-unused-value -fcxx-exceptions -std=gnu++17 -ast-dump %s \
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -fno-sized-deallocation -Wno-unused-value -fcxx-exceptions -std=gnu++17 -ast-dump %s \
 // RUN: | FileCheck --strict-whitespace %s
 //
 // Test with serialization:
-// RUN: %clang_cc1 -triple x86_64-unknown-unknown -Wno-unused-value -fcxx-exceptions -std=gnu++17 -emit-pch -o %t %s
-// RUN: %clang_cc1 -x c++ -triple x86_64-unknown-unknown -Wno-unused-value -fcxx-exceptions -std=gnu++17 \
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -fno-sized-deallocation -Wno-unused-value -fcxx-exceptions -std=gnu++17 -emit-pch -o %t %s
+// RUN: %clang_cc1 -x c++ -triple x86_64-unknown-unknown -fno-sized-deallocation -Wno-unused-value -fcxx-exceptions -std=gnu++17 \
 // RUN: -include-pch %t -ast-dump-all /dev/null \
 // RUN: | sed -e "s/ <undeserialized declarations>//" -e "s/ imported//" \
 // RUN: | FileCheck --strict-whitespace %s
diff --git a/clang/test/CodeGenCXX/cxx1y-sized-deallocation.cpp b/clang/test/CodeGenCXX/cxx1y-sized-deallocation.cpp
--- a/clang/test/CodeGenCXX/cxx1y-sized-deallocation.cpp
+++ b/clang/test/CodeGenCXX/cxx1y-sized-deallocation.cpp
@@ -5,8 +5,8 @@
 
 // Check that we don't used sized deallocation without -fsized-deallocation and
 // C++14.
-// RUN: %clang_cc1 -std=c++11 %s -emit-llvm -triple x86_64-linux-gnu -o - | FileCheck %s --check-prefix=CHECK-UNSIZED
-// RUN: %clang_cc1 -std=c++14 %s -emit-llvm -triple x86_64-linux-gnu -o - | FileCheck %s --check-prefix=CHECK-UNSIZED
+// RUN: %clang_cc1 -std=c++11 -fno-sized-deallocation %s -emit-llvm -triple x86_64-linux-gnu -o - | FileCheck %s --check-prefix=CHECK-UNSIZED
+// RUN: %clang_cc1 -std=c++14 -fno-sized-deallocation %s -emit-llvm -triple x86_64-linux-gnu -o - | FileCheck %s --check-prefix=CHECK-UNSIZED
 
 // CHECK-UNSIZED-NOT: _ZdlPvm
 // CHECK-UNSIZED-NOT: _ZdaPvm
diff --git a/clang/test/CodeGenCXX/cxx2a-destroying-delete.cpp b/clang/test/CodeGenCXX/cxx2a-destroying-delete.cpp
--- a/clang/test/CodeGenCXX/cxx2a-destroying-delete.cpp
+++ b/clang/test/CodeGenCXX/cxx2a-destroying-delete.cpp
@@ -1,11 +1,11 @@
-// RUN: %clang_cc1 -std=c++2a -fexceptions -emit-llvm %s -triple x86_64-linux-gnu -o - | FileCheck %s --check-prefixes=CHECK,CHECK-ITANIUM,CHECK-64BIT
-// RUN: %clang_cc1 -std=c++2a -fexceptions -emit-llvm %s -triple x86_64-windows -o - | FileCheck %s --check-prefixes=CHECK,CHECK-MSABI,CHECK-MSABI64,CHECK-64BIT
-// RUN: %clang_cc1 -std=c++2a -fexceptions -emit-llvm %s -triple i386-windows -o - | FileCheck %s --check-prefixes=CHECK,CHECK-MSABI,CHECK-MSABI32,CHECK-32BIT
+// RUN: %clang_cc1 -std=c++2a -fno-sized-deallocation -fexceptions -emit-llvm %s -triple x86_64-linux-gnu -o - | FileCheck %s --check-prefixes=CHECK,CHECK-ITANIUM,CHECK-64BIT
+// RUN: %clang_cc1 -std=c++2a -fno-sized-deallocation -fexceptions -emit-llvm %s -triple x86_64-windows -o - | FileCheck %s --check-prefixes=CHECK,CHECK-MSABI,CHECK-MSABI64,CHECK-64BIT
+// RUN: %clang_cc1 -std=c++2a -fno-sized-deallocation -fexceptions -emit-llvm %s -triple i386-windows -o - | FileCheck %s --check-prefixes=CHECK,CHECK-MSABI,CHECK-MSABI32,CHECK-32BIT
 
 // PR46908: ensure the IR passes the verifier with optimizations enabled.
-// RUN: %clang_cc1 -std=c++2a -fexceptions -emit-llvm-only %s -triple x86_64-linux-gnu -O2
-// RUN: %clang_cc1 -std=c++2a -fexceptions -emit-llvm-only %s -triple x86_64-windows -O2
-// RUN: %clang_cc1 -std=c++2a -fexceptions -emit-llvm-only %s -triple i386-windows -O2
+// RUN: %clang_cc1 -std=c++2a -fno-sized-deallocation -fexceptions -emit-llvm-only %s -triple x86_64-linux-gnu -O2
+// RUN: %clang_cc1 -std=c++2a -fno-sized-deallocation -fexceptions -emit-llvm-only %s -triple x86_64-windows -O2
+// RUN: %clang_cc1 -std=c++2a -fno-sized-deallocation -fexceptions -emit-llvm-only %s -triple i386-windows -O2
 
 namespace std {
   using size_t = decltype(sizeof(0));
diff --git a/clang/test/CodeGenCXX/delete-two-arg.cpp b/clang/test/CodeGenCXX/delete-two-arg.cpp
--- a/clang/test/CodeGenCXX/delete-two-arg.cpp
+++ b/clang/test/CodeGenCXX/delete-two-arg.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -triple i686-pc-linux-gnu %s -o - -emit-llvm -verify | FileCheck %s
+// RUN: %clang_cc1 -triple i686-pc-linux-gnu -fno-sized-deallocation %s -o - -emit-llvm -verify | FileCheck %s
 // expected-no-diagnostics
 
 typedef __typeof(sizeof(int)) size_t;
diff --git a/clang/test/CodeGenCXX/delete.cpp b/clang/test/CodeGenCXX/delete.cpp
--- a/clang/test/CodeGenCXX/delete.cpp
+++ b/clang/test/CodeGenCXX/delete.cpp
@@ -1,5 +1,5 @@
-// RUN: %clang_cc1 -triple x86_64-apple-darwin10 %s -emit-llvm -o - | FileCheck %s --check-prefixes=CHECK,CHECK-NOSIZE
-// RUN: %clang_cc1 -triple x86_64-apple-darwin10 %s -emit-llvm -o - -Oz -disable-llvm-passes | FileCheck %s --check-prefixes=CHECK,CHECK-SIZE
+// RUN: %clang_cc1 -triple x86_64-apple-darwin10 -fno-sized-deallocation %s -emit-llvm -o - | FileCheck %s --check-prefixes=CHECK,CHECK-NOSIZE
+// RUN: %clang_cc1 -triple x86_64-apple-darwin10 -fno-sized-deallocation %s -emit-llvm -o - -Oz -disable-llvm-passes | FileCheck %s --check-prefixes=CHECK,CHECK-SIZE
 
 void t1(int *a) {
   delete a;
diff --git a/clang/test/CodeGenCXX/new.cpp b/clang/test/CodeGenCXX/new.cpp
--- a/clang/test/CodeGenCXX/new.cpp
+++ b/clang/test/CodeGenCXX/new.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -std=c++14 -triple x86_64-unknown-unknown %s -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 -std=c++14 -fno-sized-deallocation -triple x86_64-unknown-unknown %s -emit-llvm -o - | FileCheck %s
 
 typedef __typeof__(sizeof(0)) size_t;
 
diff --git a/clang/test/CodeGenCoroutines/coro-alloc.cpp b/clang/test/CodeGenCoroutines/coro-alloc.cpp
--- a/clang/test/CodeGenCoroutines/coro-alloc.cpp
+++ b/clang/test/CodeGenCoroutines/coro-alloc.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fcoroutines-ts -std=c++14 \
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fcoroutines-ts -std=c++14 -fno-sized-deallocation \
 // RUN:    -Wno-coroutine-missing-unhandled-exception -emit-llvm %s -o - -disable-llvm-passes \
 // RUN:   | FileCheck %s
 
diff --git a/clang/test/CodeGenCoroutines/coro-cleanup.cpp b/clang/test/CodeGenCoroutines/coro-cleanup.cpp
--- a/clang/test/CodeGenCoroutines/coro-cleanup.cpp
+++ b/clang/test/CodeGenCoroutines/coro-cleanup.cpp
@@ -1,5 +1,5 @@
 // Verify that coroutine promise and allocated memory are freed up on exception.
-// RUN: %clang_cc1 -std=c++1z -fcoroutines-ts -triple=x86_64-unknown-linux-gnu -emit-llvm -o - %s -fexceptions -fcxx-exceptions -disable-llvm-passes | FileCheck %s
+// RUN: %clang_cc1 -std=c++1z -fno-sized-deallocation -fcoroutines-ts -triple=x86_64-unknown-linux-gnu -emit-llvm -o - %s -fexceptions -fcxx-exceptions -disable-llvm-passes | FileCheck %s
 
 namespace std::experimental {
 template <typename... T> struct coroutine_traits;
diff --git a/clang/test/CodeGenCoroutines/coro-gro.cpp b/clang/test/CodeGenCoroutines/coro-gro.cpp
--- a/clang/test/CodeGenCoroutines/coro-gro.cpp
+++ b/clang/test/CodeGenCoroutines/coro-gro.cpp
@@ -1,6 +1,6 @@
 // Verifies lifetime of __gro local variable
 // Verify that coroutine promise and allocated memory are freed up on exception.
-// RUN: %clang_cc1 -std=c++1z -fcoroutines-ts -triple=x86_64-unknown-linux-gnu -emit-llvm -o - %s -disable-llvm-passes | FileCheck %s
+// RUN: %clang_cc1 -std=c++1z -fno-sized-deallocation -fcoroutines-ts -triple=x86_64-unknown-linux-gnu -emit-llvm -o - %s -disable-llvm-passes | FileCheck %s
 
 namespace std::experimental {
 template <typename... T> struct coroutine_traits;
diff --git a/clang/test/SemaCXX/builtin-operator-new-delete.cpp b/clang/test/SemaCXX/builtin-operator-new-delete.cpp
--- a/clang/test/SemaCXX/builtin-operator-new-delete.cpp
+++ b/clang/test/SemaCXX/builtin-operator-new-delete.cpp
@@ -1,8 +1,8 @@
-// RUN: %clang_cc1 -std=c++1z -fsyntax-only -verify %s
-// RUN: %clang_cc1 -std=c++03 -fsyntax-only -verify %s
-// RUN: %clang_cc1 -std=c++03 -faligned-allocation -fsyntax-only -verify %s
-// RUN: %clang_cc1 -std=c++11 -fsyntax-only -verify %s
-// RUN: %clang_cc1 -std=c++11 -fsyntax-only -verify -fsized-deallocation %s
+// RUN: %clang_cc1 -std=c++1z -fno-sized-deallocation -fsyntax-only -verify %s
+// RUN: %clang_cc1 -std=c++03 -fno-sized-deallocation -fsyntax-only -verify %s
+// RUN: %clang_cc1 -std=c++03 -fno-sized-deallocation -faligned-allocation -fsyntax-only -verify %s
+// RUN: %clang_cc1 -std=c++11 -fno-sized-deallocation -fsyntax-only -verify %s
+// RUN: %clang_cc1 -std=c++11 -fno-sized-deallocation -fsyntax-only -verify -fsized-deallocation %s
 
 #if !__has_builtin(__builtin_operator_new) || !__has_builtin(__builtin_operator_delete)
 #error builtins should always be available
diff --git a/clang/test/SemaCXX/unavailable_aligned_allocation.cpp b/clang/test/SemaCXX/unavailable_aligned_allocation.cpp
--- a/clang/test/SemaCXX/unavailable_aligned_allocation.cpp
+++ b/clang/test/SemaCXX/unavailable_aligned_allocation.cpp
@@ -1,15 +1,15 @@
-// RUN: %clang_cc1 -triple x86_64-apple-macosx10.13.0 -fexceptions -faligned-alloc-unavailable -std=c++1z -verify -DMACOS %s
-// RUN: %clang_cc1 -triple x86_64-apple-macosx10.13.0 -fexceptions -std=c++1z -verify -DNO_ERRORS %s
-// RUN: %clang_cc1 -triple x86_64-apple-macosx10.13.0 -fexceptions -faligned-allocation -faligned-alloc-unavailable -std=c++14 -verify -DMACOS %s
-// RUN: %clang_cc1 -triple arm64-apple-ios10.0.0 -fexceptions -faligned-alloc-unavailable -std=c++1z -verify -DIOS %s
-// RUN: %clang_cc1 -triple arm64-apple-ios10.0.0 -fexceptions -std=c++1z -verify -DNO_ERRORS %s
-// RUN: %clang_cc1 -triple arm64-apple-tvos10.0.0 -fexceptions -faligned-alloc-unavailable -std=c++1z -verify -DTVOS %s
-// RUN: %clang_cc1 -triple arm64-apple-tvos10.0.0 -fexceptions -std=c++1z -verify -DNO_ERRORS %s
-// RUN: %clang_cc1 -triple armv7k-apple-watchos3.0.0 -fexceptions -faligned-alloc-unavailable -std=c++1z -verify -DWATCHOS %s
-// RUN: %clang_cc1 -triple armv7k-apple-watchos3.0.0 -fexceptions -std=c++1z -verify -DNO_ERRORS %s
-// RUN: %clang_cc1 -triple s390x-none-zos -fexceptions -faligned-alloc-unavailable -std=c++1z -verify -DZOS %s
-// RUN: %clang_cc1 -triple s390x-none-zos -fexceptions -std=c++1z -verify -DNO_ERRORS %s
-// RUN: %clang_cc1 -triple s390x-none-zos -fexceptions -faligned-allocation -faligned-alloc-unavailable -std=c++14 -verify -DZOS %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.13.0 -fno-sized-deallocation -fexceptions -faligned-alloc-unavailable -std=c++1z -verify -DMACOS %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.13.0 -fno-sized-deallocation -fexceptions -std=c++1z -verify -DNO_ERRORS %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.13.0 -fno-sized-deallocation -fexceptions -faligned-allocation -faligned-alloc-unavailable -std=c++14 -verify -DMACOS %s
+// RUN: %clang_cc1 -triple arm64-apple-ios10.0.0 -fno-sized-deallocation -fexceptions -faligned-alloc-unavailable -std=c++1z -verify -DIOS %s
+// RUN: %clang_cc1 -triple arm64-apple-ios10.0.0 -fno-sized-deallocation -fexceptions -std=c++1z -verify -DNO_ERRORS %s
+// RUN: %clang_cc1 -triple arm64-apple-tvos10.0.0 -fno-sized-deallocation -fexceptions -faligned-alloc-unavailable -std=c++1z -verify -DTVOS %s
+// RUN: %clang_cc1 -triple arm64-apple-tvos10.0.0 -fno-sized-deallocation -fexceptions -std=c++1z -verify -DNO_ERRORS %s
+// RUN: %clang_cc1 -triple armv7k-apple-watchos3.0.0 -fno-sized-deallocation -fexceptions -faligned-alloc-unavailable -std=c++1z -verify -DWATCHOS %s
+// RUN: %clang_cc1 -triple armv7k-apple-watchos3.0.0 -fno-sized-deallocation -fexceptions -std=c++1z -verify -DNO_ERRORS %s
+// RUN: %clang_cc1 -triple s390x-none-zos -fexceptions -fno-sized-deallocation -faligned-alloc-unavailable -std=c++1z -verify -DZOS %s
+// RUN: %clang_cc1 -triple s390x-none-zos -fexceptions -fno-sized-deallocation -std=c++1z -verify -DNO_ERRORS %s
+// RUN: %clang_cc1 -triple s390x-none-zos -fexceptions -fno-sized-deallocation -faligned-allocation -faligned-alloc-unavailable -std=c++14 -verify -DZOS %s
 
 namespace std {
   typedef decltype(sizeof(0)) size_t;
diff --git a/clang/unittests/StaticAnalyzer/CallEventTest.cpp b/clang/unittests/StaticAnalyzer/CallEventTest.cpp
--- a/clang/unittests/StaticAnalyzer/CallEventTest.cpp
+++ b/clang/unittests/StaticAnalyzer/CallEventTest.cpp
@@ -81,7 +81,7 @@
     }
   )",
                                                          Diags));
-  EXPECT_EQ(Diags, "test.CXXDeallocator: NumArgs: 1\n");
+  EXPECT_EQ(Diags, "test.CXXDeallocator: NumArgs: 2\n");
 }
 
 } // namespace
diff --git a/clang/www/cxx_status.html b/clang/www/cxx_status.html
--- a/clang/www/cxx_status.html
+++ b/clang/www/cxx_status.html
@@ -578,12 +578,11 @@
 </table>
 
 <p>
-<span id="n3778">(7): In Clang 3.7 and later, sized deallocation is only enabled
-if the user passes the <code>-fsized-deallocation</code> flag. The user must
-supply definitions of the sized deallocation functions, either by providing them
-explicitly or by using a C++ standard library that does. <code>libstdc++</code>
-added these functions in version 5.0, and <code>libc++</code> added them in
-version 3.7.
+<span id="n3778">(7): The user must supply definitions of the sized deallocation
+functions, either by providing them explicitly or by using a C++ standard library
+that does. <code>libstdc++</code> added these functions in version 5.0, and
+<code>libc++</code> added them in version 3.7. The user can also use the
+<code>-fno-sized-deallocation</code> option to disable sized deallocation.
 </span>
 </p>
 </details>