diff --git a/clang/include/clang/Basic/AlignedAllocation.h b/clang/include/clang/Basic/AlignedAllocation.h
--- a/clang/include/clang/Basic/AlignedAllocation.h
+++ b/clang/include/clang/Basic/AlignedAllocation.h
@@ -33,6 +33,8 @@
     return llvm::VersionTuple(11U);
   case llvm::Triple::WatchOS: // Earliest supporting version is 4.0.0.
     return llvm::VersionTuple(4U);
+  case llvm::Triple::ZOS:
+    return llvm::VersionTuple(); // All z/OS versions have no support.
   }
 
   llvm_unreachable("Unexpected OS");
diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -825,6 +825,7 @@
              .Case("macos_app_extension", "macOSApplicationExtension")
              .Case("tvos_app_extension", "tvOSApplicationExtension")
              .Case("watchos_app_extension", "watchOSApplicationExtension")
+             .Case("zos", "z/OS")
              .Default(Platform);
 }
 static llvm::StringRef canonicalizePlatformName(llvm::StringRef Platform) {
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -7219,8 +7219,8 @@
   "guarantees %2 bytes">,
   InGroup<OveralignedType>, DefaultIgnore;
 def err_aligned_allocation_unavailable : Error<
-  "aligned %select{allocation|deallocation}0 function of type '%1' is only "
-  "available on %2 %3 or newer">;
+  "aligned %select{allocation|deallocation}0 function of type '%1' is "
+  "%select{only|not}4 available on %2%select{ %3 or newer|}4">;
 def note_silence_aligned_allocation_unavailable : Note<
   "if you supply your own aligned allocation functions, use "
   "-faligned-allocation to silence this diagnostic">;
diff --git a/clang/lib/Basic/Targets/OSTargets.h b/clang/lib/Basic/Targets/OSTargets.h
--- a/clang/lib/Basic/Targets/OSTargets.h
+++ b/clang/lib/Basic/Targets/OSTargets.h
@@ -770,6 +770,8 @@
       // type is not declared as a typedef in system headers.
       Builder.defineMacro("__wchar_t");
     }
+
+    this->PlatformName = llvm::Triple::getOSTypeName(Triple.getOS());
   }
 
 public:
diff --git a/clang/lib/Driver/ToolChains/ZOS.h b/clang/lib/Driver/ToolChains/ZOS.h
--- a/clang/lib/Driver/ToolChains/ZOS.h
+++ b/clang/lib/Driver/ToolChains/ZOS.h
@@ -27,6 +27,10 @@
   bool isPICDefaultForced() const override { return false; }
 
   bool IsIntegratedAssemblerDefault() const override { return true; }
+
+  void addClangTargetOptions(
+      const llvm::opt::ArgList &DriverArgs, llvm::opt::ArgStringList &CC1Args,
+      Action::OffloadKind DeviceOffloadingKind) const override;
 };
 
 } // end namespace toolchains
diff --git a/clang/lib/Driver/ToolChains/ZOS.cpp b/clang/lib/Driver/ToolChains/ZOS.cpp
--- a/clang/lib/Driver/ToolChains/ZOS.cpp
+++ b/clang/lib/Driver/ToolChains/ZOS.cpp
@@ -21,3 +21,13 @@
     : ToolChain(D, Triple, Args) {}
 
 ZOS::~ZOS() {}
+
+void ZOS::addClangTargetOptions(const ArgList &DriverArgs,
+                                ArgStringList &CC1Args,
+                                Action::OffloadKind DeviceOffloadKind) const {
+  // Pass "-faligned-alloc-unavailable" only when the user hasn't manually
+  // enabled or disabled aligned allocations.
+  if (!DriverArgs.hasArgNoClaim(options::OPT_faligned_allocation,
+                                options::OPT_fno_aligned_allocation))
+    CC1Args.push_back("-faligned-alloc-unavailable");
+}
diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -1843,12 +1843,13 @@
     const llvm::Triple &T = getASTContext().getTargetInfo().getTriple();
     StringRef OSName = AvailabilityAttr::getPlatformNameSourceSpelling(
         getASTContext().getTargetInfo().getPlatformName());
+    VersionTuple OSVersion = alignedAllocMinVersion(T.getOS());
 
     OverloadedOperatorKind Kind = FD.getDeclName().getCXXOverloadedOperator();
     bool IsDelete = Kind == OO_Delete || Kind == OO_Array_Delete;
     Diag(Loc, diag::err_aligned_allocation_unavailable)
         << IsDelete << FD.getType().getAsString() << OSName
-        << alignedAllocMinVersion(T.getOS()).getAsString();
+        << OSVersion.getAsString() << OSVersion.empty();
     Diag(Loc, diag::note_silence_aligned_allocation_unavailable);
   }
 }
diff --git a/clang/test/Driver/unavailable_aligned_allocation.cpp b/clang/test/Driver/unavailable_aligned_allocation.cpp
--- a/clang/test/Driver/unavailable_aligned_allocation.cpp
+++ b/clang/test/Driver/unavailable_aligned_allocation.cpp
@@ -22,6 +22,9 @@
 // RUN: -c -### %s 2>&1 \
 // RUN:   | FileCheck %s -check-prefix=UNAVAILABLE
 //
+// RUN: %clang -target s390x-none-zos -c -### %s 2>&1 \
+// RUN:   | FileCheck %s -check-prefix=UNAVAILABLE
+
 // UNAVAILABLE: "-faligned-alloc-unavailable"
 
 // RUN: %clang -target x86_64-apple-macosx10.14 -c -### %s 2>&1 \
@@ -59,5 +62,11 @@
 //
 // RUN: %clang -target x86_64-apple-macosx10.13 -fno-aligned-allocation -c -### %s 2>&1 \
 // RUN:   | FileCheck %s -check-prefix=AVAILABLE
+//
+// RUN: %clang -target s390x-none-zos -faligned-allocation -c -### %s 2>&1 \
+// RUN:   | FileCheck %s -check-prefix=AVAILABLE
+//
+// RUN: %clang -target s390x-none-zos -fno-aligned-allocation -c -### %s 2>&1 \
+// RUN:   | FileCheck %s -check-prefix=AVAILABLE
 
 // AVAILABLE-NOT: "-faligned-alloc-unavailable"
diff --git a/clang/test/Lexer/aligned-allocation.cpp b/clang/test/Lexer/aligned-allocation.cpp
--- a/clang/test/Lexer/aligned-allocation.cpp
+++ b/clang/test/Lexer/aligned-allocation.cpp
@@ -6,10 +6,19 @@
 //
 // RUN: %clang_cc1 -triple x86_64-apple-macosx10.12.0 -fexceptions -std=c++17 -verify %s \
 // RUN:   -faligned-allocation -faligned-alloc-unavailable
+//
+// RUN: %clang_cc1 -triple s390x-none-zos -fexceptions -std=c++17 -verify %s \
+// RUN:   -DEXPECT_DEFINED
+//
+// RUN: %clang_cc1 -triple s390x-none-zos -fexceptions -std=c++17 -verify %s \
+// RUN:   -faligned-alloc-unavailable
+//
+// RUN: %clang_cc1 -triple s390x-none-zos -fexceptions -std=c++17 -verify %s \
+// RUN:   -faligned-allocation -faligned-alloc-unavailable
 
 // Test that __cpp_aligned_new is not defined when CC1 is passed
-// -faligned-alloc-unavailable by the Darwin driver, even when aligned
-// allocation is actually enabled.
+// -faligned-alloc-unavailable by the Darwin and the z/OS driver, even when
+// aligned allocation is actually enabled.
 
 // expected-no-diagnostics
 #ifdef EXPECT_DEFINED
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
@@ -1,12 +1,15 @@
-// RUN: %clang_cc1 -triple x86_64-apple-macosx10.13.0 -fexceptions -faligned-alloc-unavailable -std=c++1z -verify %s
+// 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 %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
 
 namespace std {
   typedef decltype(sizeof(0)) size_t;
@@ -62,40 +65,40 @@
 #ifdef NO_ERRORS
 // expected-no-diagnostics
 #else
-// expected-error@-16 {{aligned allocation function of type 'void *(unsigned long, enum std::align_val_t)' is only available on}}
+// expected-error-re@-16 {{aligned allocation function of type 'void *(unsigned long, enum std::align_val_t)' is {{only|not}} available on}}
 // expected-note@-17 {{if you supply your own aligned allocation functions}}
-// expected-error@-18 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is only available on}}
+// expected-error-re@-18 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is {{only|not}} available on}}
 // expected-note@-19 {{if you supply your own aligned allocation functions}}
 
-// expected-error@-20 {{aligned allocation function of type 'void *(unsigned long, enum std::align_val_t)' is only available on}}
+// expected-error-re@-20 {{aligned allocation function of type 'void *(unsigned long, enum std::align_val_t)' is {{only|not}} available on}}
 // expected-note@-21 {{if you supply your own aligned allocation functions}}
-// expected-error@-22 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is only available on}}
+// expected-error-re@-22 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is {{only|not}} available on}}
 // expected-note@-23 {{if you supply your own aligned allocation functions}}
 
-// expected-error@-24 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is only available on}}
+// expected-error-re@-24 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is {{only|not}} available on}}
 // expected-note@-25 {{if you supply your own aligned allocation functions}}
 
-// expected-error@-26 {{aligned allocation function of type 'void *(std::size_t, std::align_val_t, const std::nothrow_t &) noexcept' is only available on}}
+// expected-error-re@-26 {{aligned allocation function of type 'void *(std::size_t, std::align_val_t, const std::nothrow_t &) noexcept' is {{only|not}} available on}}
 // expected-note@-27 {{if you supply your own aligned allocation functions}}
-// expected-error@-28 {{aligned deallocation function of type 'void (void *, std::align_val_t, const std::nothrow_t &) noexcept' is only available on}}
+// expected-error-re@-28 {{aligned deallocation function of type 'void (void *, std::align_val_t, const std::nothrow_t &) noexcept' is {{only|not}} available on}}
 // expected-note@-29 {{if you supply your own aligned allocation functions}}
 
-// expected-error@-29 {{aligned allocation function of type 'void *(unsigned long, enum std::align_val_t)' is only available on}}
+// expected-error-re@-29 {{aligned allocation function of type 'void *(unsigned long, enum std::align_val_t)' is {{only|not}} available on}}
 // expected-note@-30 {{if you supply your own aligned allocation functions}}
-// expected-error@-31 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is only available on}}
+// expected-error-re@-31 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is {{only|not}} available on}}
 // expected-note@-32 {{if you supply your own aligned allocation functions}}
 
-// expected-error@-33 {{aligned allocation function of type 'void *(unsigned long, enum std::align_val_t)' is only available on}}
+// expected-error-re@-33 {{aligned allocation function of type 'void *(unsigned long, enum std::align_val_t)' is {{only|not}} available on}}
 // expected-note@-34 {{if you supply your own aligned allocation functions}}
-// expected-error@-35 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is only available on}}
+// expected-error-re@-35 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is {{only|not}} available on}}
 // expected-note@-36 {{if you supply your own aligned allocation functions}}
 
-// expected-error@-37 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is only available on}}
+// expected-error-re@-37 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is {{only|not}} available on}}
 // expected-note@-38 {{if you supply your own aligned allocation functions}}
 
-// expected-error@-39 {{aligned allocation function of type 'void *(std::size_t, std::align_val_t, const std::nothrow_t &) noexcept' is only available on}}
+// expected-error-re@-39 {{aligned allocation function of type 'void *(std::size_t, std::align_val_t, const std::nothrow_t &) noexcept' is {{only|not}} available on}}
 // expected-note@-40 {{if you supply your own aligned allocation functions}}
-// expected-error@-41 {{aligned deallocation function of type 'void (void *, std::align_val_t, const std::nothrow_t &) noexcept' is only available on}}
+// expected-error-re@-41 {{aligned deallocation function of type 'void (void *, std::align_val_t, const std::nothrow_t &) noexcept' is {{only|not}} available on}}
 // expected-note@-42 {{if you supply your own aligned allocation functions}}
 
 #endif
@@ -116,12 +119,15 @@
 #elif defined(WATCHOS)
 // expected-error@-13 {{aligned allocation function of type 'void *(unsigned long, enum std::align_val_t)' is only available on watchOS 4 or newer}}}
 // expected-error@-14 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is only available on watchOS 4 or newer}}}
-#else
+#elif defined(MACOS)
 // expected-error@-16 {{aligned allocation function of type 'void *(unsigned long, enum std::align_val_t)' is only available on macOS 10.14 or newer}}}
 // expected-error@-17 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is only available on macOS 10.14 or newer}}}
+#elif defined(ZOS)
+// expected-error@-19 {{aligned allocation function of type 'void *(unsigned long, enum std::align_val_t)' is not available on z/OS}}}
+// expected-error@-20 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is not available on z/OS}}}
 #endif
 
-// expected-note@-20 2 {{if you supply your own aligned allocation functions}}
+// expected-note@-23 2 {{if you supply your own aligned allocation functions}}
 #endif
 
 // Test that diagnostics are produced when an unavailable aligned deallocation
@@ -145,9 +151,12 @@
 #elif defined(WATCHOS)
 // expected-error@-12 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is only available on watchOS 4 or newer}}}
 // expected-note@-13 {{if you supply your own aligned allocation functions}}
-#else
+#elif defined(MACOS)
 // expected-error@-15 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is only available on macOS 10.14 or newer}}}
 // expected-note@-16 {{if you supply your own aligned allocation functions}}
+#elif defined(ZOS)
+// expected-error@-18 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is not available on z/OS}}}
+// expected-note@-19 {{if you supply your own aligned allocation functions}}
 #endif
 #endif
 
@@ -172,22 +181,22 @@
 #ifdef NO_ERRORS
 // expected-no-diagnostics
 #else
-// expected-error@-11 {{aligned allocation function of type 'void *(unsigned long, enum std::align_val_t)' is only available on}}
+// expected-error-re@-11 {{aligned allocation function of type 'void *(unsigned long, enum std::align_val_t)' is {{only|not}} available on}}
 // expected-note@-12 {{if you supply your own aligned allocation functions}}
 
-// expected-error@-13 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is only available on}}
+// expected-error-re@-13 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is {{only|not}} available on}}
 // expected-note@-14 {{if you supply your own aligned allocation functions}}
 
-// expected-error@-15 {{aligned allocation function of type 'void *(unsigned long, enum std::align_val_t)' is only available on}}
+// expected-error-re@-15 {{aligned allocation function of type 'void *(unsigned long, enum std::align_val_t)' is {{only|not}} available on}}
 // expected-note@-16 {{if you supply your own aligned allocation functions}}
 
-// expected-error@-17 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is only available on}}
+// expected-error-re@-17 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is {{only|not}} available on}}
 // expected-note@-18 {{if you supply your own aligned allocation functions}}
 
-// expected-error@-19 {{aligned allocation function of type 'void *(unsigned long, enum std::align_val_t)' is only available on}}
+// expected-error-re@-19 {{aligned allocation function of type 'void *(unsigned long, enum std::align_val_t)' is {{only|not}} available on}}
 // expected-note@-20 {{if you supply your own aligned allocation functions}}
 
-// expected-error@-21 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is only available on}}
+// expected-error-re@-21 {{aligned deallocation function of type 'void (void *, enum std::align_val_t) noexcept' is {{only|not}} available on}}
 // expected-note@-22 {{if you supply your own aligned allocation functions}}
 #endif