Index: clang/lib/CodeGen/TargetInfo.cpp
===================================================================
--- clang/lib/CodeGen/TargetInfo.cpp
+++ clang/lib/CodeGen/TargetInfo.cpp
@@ -2508,12 +2508,15 @@
                                  const llvm::StringMap<bool> &CallerMap,
                                  const llvm::StringMap<bool> &CalleeMap,
                                  QualType Ty, StringRef Feature,
-                                 bool IsArgument) {
+                                 bool IsArgument, bool EnableWarning) {
   bool CallerHasFeat = CallerMap.lookup(Feature);
   bool CalleeHasFeat = CalleeMap.lookup(Feature);
-  if (!CallerHasFeat && !CalleeHasFeat)
+  if (!CallerHasFeat && !CalleeHasFeat) {
+    if (!EnableWarning)
+      return false;
     return Diag.Report(CallLoc, diag::warn_avx_calling_convention)
            << IsArgument << Ty << Feature;
+  }
 
   // Mixing calling conventions here is very clearly an error.
   if (!CallerHasFeat || !CalleeHasFeat)
@@ -2530,14 +2533,20 @@
                           const llvm::StringMap<bool> &CallerMap,
                           const llvm::StringMap<bool> &CalleeMap, QualType Ty,
                           bool IsArgument) {
+  // Note: Darwin x86_64 targets a baseline CPU which doesn't enable
+  // AVX/AVX512, so it allows passing wide vectors in SSE: don't warn.
+  // Darwin users who do enable AVX/AVX512 are responsible for ensuring safe
+  // usage of wide vector types.
+  // However, x86_64h does enable AVX by default in all functions.
+  bool EnableWarning = !Ctx.getTargetInfo().getTriple().isOSDarwin();
   uint64_t Size = Ctx.getTypeSize(Ty);
   if (Size > 256)
     return checkAVXParamFeature(Diag, CallLoc, CallerMap, CalleeMap, Ty,
-                                "avx512f", IsArgument);
+                                "avx512f", IsArgument, EnableWarning);
 
   if (Size > 128)
     return checkAVXParamFeature(Diag, CallLoc, CallerMap, CalleeMap, Ty, "avx",
-                                IsArgument);
+                                IsArgument, EnableWarning);
 
   return false;
 }
Index: clang/test/CodeGen/target-avx-abi-diag.c
===================================================================
--- clang/test/CodeGen/target-avx-abi-diag.c
+++ clang/test/CodeGen/target-avx-abi-diag.c
@@ -1,6 +1,9 @@
-// RUN: %clang_cc1 %s -triple=x86_64-linux-gnu -verify=no256,no512 -o - -S
-// RUN: %clang_cc1 %s -triple=x86_64-linux-gnu -target-feature +avx -verify=no512 -o - -S
+// RUN: %clang_cc1 %s -triple=x86_64-linux-gnu -verify=no256,no512,no256-err,no512-err -o - -S
+// RUN: %clang_cc1 %s -triple=x86_64-linux-gnu -target-feature +avx -verify=no512,no512-err -o - -S
 // RUN: %clang_cc1 %s -triple=x86_64-linux-gnu -target-feature +avx512f -verify=both -o - -S
+
+// RUN: %clang_cc1 %s -triple=x86_64-apple-macos -verify=no256-err,no512-err -o - -S
+// RUN: %clang_cc1 %s -triple=x86_64-apple-macos -target-feature +avx -verify=no512-err -o - -S
 // REQUIRES: x86-registered-target
 
 // both-no-diagnostics
@@ -31,12 +34,12 @@
 // If only 1 side has an attribute, error.
 void call_errors(void) {
   avx256Type t1;
-  takesAvx256(t1); // no256-error {{AVX vector argument of type 'avx256Type' (vector of 16 'short' values) without 'avx' enabled changes the ABI}}
+  takesAvx256(t1); // no256-err-error {{AVX vector argument of type 'avx256Type' (vector of 16 'short' values) without 'avx' enabled changes the ABI}}
   avx512fType t2;
-  takesAvx512(t2); // no512-error {{AVX vector argument of type 'avx512fType' (vector of 32 'short' values) without 'avx512f' enabled changes the ABI}}
+  takesAvx512(t2); // no512-err-error {{AVX vector argument of type 'avx512fType' (vector of 32 'short' values) without 'avx512f' enabled changes the ABI}}
 
-  variadic_err(1, t1); // no256-error {{AVX vector argument of type 'avx256Type' (vector of 16 'short' values) without 'avx' enabled changes the ABI}}
-  variadic_err(3, t2); // no512-error {{AVX vector argument of type 'avx512fType' (vector of 32 'short' values) without 'avx512f' enabled changes the ABI}}
+  variadic_err(1, t1); // no256-err-error {{AVX vector argument of type 'avx256Type' (vector of 16 'short' values) without 'avx' enabled changes the ABI}}
+  variadic_err(3, t2); // no512-err-error {{AVX vector argument of type 'avx512fType' (vector of 32 'short' values) without 'avx512f' enabled changes the ABI}}
 }
 
 // These two don't diagnose anything, since these are valid calls.
Index: clang/test/CodeGen/target-builtin-error-3.c
===================================================================
--- clang/test/CodeGen/target-builtin-error-3.c
+++ clang/test/CodeGen/target-builtin-error-3.c
@@ -24,6 +24,5 @@
 }
 void avx_test( uint16_t *destData, float16 argbF)
 {
-  // expected-warning@+1{{AVX vector argument of type 'float16' (vector of 16 'float' values) without 'avx512f' enabled changes the ABI}}
   ((half16U *)destData)[0] = convert_half(argbF);
 }