diff --git a/clang/include/clang/Basic/Diagnostic.td b/clang/include/clang/Basic/Diagnostic.td
--- a/clang/include/clang/Basic/Diagnostic.td
+++ b/clang/include/clang/Basic/Diagnostic.td
@@ -84,6 +84,7 @@
   bit            AccessControl = 0;
   bit            WarningNoWerror = 0;
   bit            ShowInSystemHeader = 0;
+  bit            ShowInSystemMacro = 1;
   bit            Deferrable = 0;
   Severity       DefaultSeverity = defaultmapping;
   DiagGroup      Group;
@@ -108,6 +109,14 @@
   bit ShowInSystemHeader = 0;
 }
 
+class ShowInSystemMacro {
+  bit ShowInSystemMacro = 1;
+}
+
+class SuppressInSystemMacro {
+  bit ShowInSystemMacro = 0;
+}
+
 class Deferrable {
   bit Deferrable = 1;
 }
@@ -159,4 +168,3 @@
 include "DiagnosticRefactoringKinds.td"
 include "DiagnosticSemaKinds.td"
 include "DiagnosticSerializationKinds.td"
-
diff --git a/clang/include/clang/Basic/DiagnosticAST.h b/clang/include/clang/Basic/DiagnosticAST.h
--- a/clang/include/clang/Basic/DiagnosticAST.h
+++ b/clang/include/clang/Basic/DiagnosticAST.h
@@ -15,7 +15,7 @@
 namespace diag {
 enum {
 #define DIAG(ENUM, FLAGS, DEFAULT_MAPPING, DESC, GROUP, SFINAE, NOWERROR,      \
-             SHOWINSYSHEADER, DEFERRABLE, CATEGORY)                            \
+             SHOWINSYSHEADER, SHOWINSYSMACRO, DEFERRABLE, CATEGORY)            \
   ENUM,
 #define ASTSTART
 #include "clang/Basic/DiagnosticASTKinds.inc"
diff --git a/clang/include/clang/Basic/DiagnosticAnalysis.h b/clang/include/clang/Basic/DiagnosticAnalysis.h
--- a/clang/include/clang/Basic/DiagnosticAnalysis.h
+++ b/clang/include/clang/Basic/DiagnosticAnalysis.h
@@ -15,7 +15,7 @@
 namespace diag {
 enum {
 #define DIAG(ENUM, FLAGS, DEFAULT_MAPPING, DESC, GROUP, SFINAE, NOWERROR,      \
-             SHOWINSYSHEADER, DEFERRABLE, CATEGORY)                            \
+             SHOWINSYSHEADER, SHOWINSYSMACRO, DEFERRABLE, CATEGORY)            \
   ENUM,
 #define ANALYSISSTART
 #include "clang/Basic/DiagnosticAnalysisKinds.inc"
diff --git a/clang/include/clang/Basic/DiagnosticComment.h b/clang/include/clang/Basic/DiagnosticComment.h
--- a/clang/include/clang/Basic/DiagnosticComment.h
+++ b/clang/include/clang/Basic/DiagnosticComment.h
@@ -15,7 +15,7 @@
 namespace diag {
 enum {
 #define DIAG(ENUM, FLAGS, DEFAULT_MAPPING, DESC, GROUP, SFINAE, NOWERROR,      \
-             SHOWINSYSHEADER, DEFERRABLE, CATEGORY)                            \
+             SHOWINSYSHEADER, SHOWINSYSMACRO, DEFERRABLE, CATEGORY)            \
   ENUM,
 #define COMMENTSTART
 #include "clang/Basic/DiagnosticCommentKinds.inc"
diff --git a/clang/include/clang/Basic/DiagnosticCrossTU.h b/clang/include/clang/Basic/DiagnosticCrossTU.h
--- a/clang/include/clang/Basic/DiagnosticCrossTU.h
+++ b/clang/include/clang/Basic/DiagnosticCrossTU.h
@@ -15,7 +15,7 @@
 namespace diag {
 enum {
 #define DIAG(ENUM, FLAGS, DEFAULT_MAPPING, DESC, GROUP, SFINAE, NOWERROR,      \
-             SHOWINSYSHEADER, DEFERRABLE, CATEGORY)                            \
+             SHOWINSYSHEADER, SHOWINSYSMACRO, DEFERRABLE, CATEGORY)            \
   ENUM,
 #define CROSSTUSTART
 #include "clang/Basic/DiagnosticCrossTUKinds.inc"
diff --git a/clang/include/clang/Basic/DiagnosticDriver.h b/clang/include/clang/Basic/DiagnosticDriver.h
--- a/clang/include/clang/Basic/DiagnosticDriver.h
+++ b/clang/include/clang/Basic/DiagnosticDriver.h
@@ -15,7 +15,7 @@
 namespace diag {
 enum {
 #define DIAG(ENUM, FLAGS, DEFAULT_MAPPING, DESC, GROUP, SFINAE, NOWERROR,      \
-             SHOWINSYSHEADER, DEFERRABLE, CATEGORY)                            \
+             SHOWINSYSHEADER, SHOWINSYSMACRO, DEFERRABLE, CATEGORY)            \
   ENUM,
 #define DRIVERSTART
 #include "clang/Basic/DiagnosticDriverKinds.inc"
diff --git a/clang/include/clang/Basic/DiagnosticFrontend.h b/clang/include/clang/Basic/DiagnosticFrontend.h
--- a/clang/include/clang/Basic/DiagnosticFrontend.h
+++ b/clang/include/clang/Basic/DiagnosticFrontend.h
@@ -15,7 +15,7 @@
 namespace diag {
 enum {
 #define DIAG(ENUM, FLAGS, DEFAULT_MAPPING, DESC, GROUP, SFINAE, NOWERROR,      \
-             SHOWINSYSHEADER, DEFERRABLE, CATEGORY)                            \
+             SHOWINSYSHEADER, SHOWINSYSMACRO, DEFERRABLE, CATEGORY)            \
   ENUM,
 #define FRONTENDSTART
 #include "clang/Basic/DiagnosticFrontendKinds.inc"
diff --git a/clang/include/clang/Basic/DiagnosticIDs.h b/clang/include/clang/Basic/DiagnosticIDs.h
--- a/clang/include/clang/Basic/DiagnosticIDs.h
+++ b/clang/include/clang/Basic/DiagnosticIDs.h
@@ -67,7 +67,7 @@
     // Get typedefs for common diagnostics.
     enum {
 #define DIAG(ENUM, FLAGS, DEFAULT_MAPPING, DESC, GROUP, SFINAE, CATEGORY,      \
-             NOWERROR, SHOWINSYSHEADER, DEFFERABLE)                            \
+             NOWERROR, SHOWINSYSHEADER, SHOWINSYSMACRO, DEFFERABLE)            \
   ENUM,
 #define COMMONSTART
 #include "clang/Basic/DiagnosticCommonKinds.inc"
diff --git a/clang/include/clang/Basic/DiagnosticLex.h b/clang/include/clang/Basic/DiagnosticLex.h
--- a/clang/include/clang/Basic/DiagnosticLex.h
+++ b/clang/include/clang/Basic/DiagnosticLex.h
@@ -15,7 +15,7 @@
 namespace diag {
 enum {
 #define DIAG(ENUM, FLAGS, DEFAULT_MAPPING, DESC, GROUP, SFINAE, NOWERROR,      \
-             SHOWINSYSHEADER, DEFERRABLE, CATEGORY)                            \
+             SHOWINSYSHEADER, SHOWINSYSMACRO, DEFERRABLE, CATEGORY)            \
   ENUM,
 #define LEXSTART
 #include "clang/Basic/DiagnosticLexKinds.inc"
diff --git a/clang/include/clang/Basic/DiagnosticParse.h b/clang/include/clang/Basic/DiagnosticParse.h
--- a/clang/include/clang/Basic/DiagnosticParse.h
+++ b/clang/include/clang/Basic/DiagnosticParse.h
@@ -15,7 +15,7 @@
 namespace diag {
 enum {
 #define DIAG(ENUM, FLAGS, DEFAULT_MAPPING, DESC, GROUP, SFINAE, NOWERROR,      \
-             SHOWINSYSHEADER, DEFERRABLE, CATEGORY)                            \
+             SHOWINSYSHEADER, SHOWINSYSMACRO, DEFERRABLE, CATEGORY)            \
   ENUM,
 #define PARSESTART
 #include "clang/Basic/DiagnosticParseKinds.inc"
diff --git a/clang/include/clang/Basic/DiagnosticRefactoring.h b/clang/include/clang/Basic/DiagnosticRefactoring.h
--- a/clang/include/clang/Basic/DiagnosticRefactoring.h
+++ b/clang/include/clang/Basic/DiagnosticRefactoring.h
@@ -15,7 +15,7 @@
 namespace diag {
 enum {
 #define DIAG(ENUM, FLAGS, DEFAULT_MAPPING, DESC, GROUP, SFINAE, NOWERROR,      \
-             SHOWINSYSHEADER, DEFERRABLE, CATEGORY)                            \
+             SHOWINSYSHEADER, SHOWINSYSMACRO, DEFERRABLE, CATEGORY)            \
   ENUM,
 #define REFACTORINGSTART
 #include "clang/Basic/DiagnosticRefactoringKinds.inc"
diff --git a/clang/include/clang/Basic/DiagnosticSema.h b/clang/include/clang/Basic/DiagnosticSema.h
--- a/clang/include/clang/Basic/DiagnosticSema.h
+++ b/clang/include/clang/Basic/DiagnosticSema.h
@@ -15,7 +15,7 @@
 namespace diag {
 enum {
 #define DIAG(ENUM, FLAGS, DEFAULT_MAPPING, DESC, GROUP, SFINAE, NOWERROR,      \
-             SHOWINSYSHEADER, DEFERRABLE, CATEGORY)                            \
+             SHOWINSYSHEADER, SHOWINSYSMACRO, DEFERRABLE, CATEGORY)            \
   ENUM,
 #define SEMASTART
 #include "clang/Basic/DiagnosticSemaKinds.inc"
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
@@ -197,7 +197,8 @@
 
 // C++20 designated initializers
 def ext_cxx_designated_init : Extension<
-  "designated initializers are a C++20 extension">, InGroup<CXX20Designator>;
+  "designated initializers are a C++20 extension">, InGroup<CXX20Designator>,
+  SuppressInSystemMacro;
 def warn_cxx17_compat_designated_init : Warning<
   "designated initializers are incompatible with C++ standards before C++20">,
   InGroup<CXXPre20CompatPedantic>, DefaultIgnore;
@@ -449,7 +450,7 @@
           "typedef in %2|"
           "type alias in %2|"
           "structured binding}1">,
-  InGroup<Shadow>, DefaultIgnore;
+  InGroup<Shadow>, DefaultIgnore, SuppressInSystemMacro;
 def warn_decl_shadow_uncaptured_local :
   Warning<warn_decl_shadow.Text>,
   InGroup<ShadowUncapturedLocal>, DefaultIgnore;
@@ -3944,7 +3945,8 @@
   "cast from %0 to %1 increases required alignment from %2 to %3">,
   InGroup<CastAlign>, DefaultIgnore;
 def warn_old_style_cast : Warning<
-  "use of old-style cast">, InGroup<OldStyleCast>, DefaultIgnore;
+  "use of old-style cast">, InGroup<OldStyleCast>, DefaultIgnore,
+  SuppressInSystemMacro;
 
 // Separate between casts to void* and non-void* pointers.
 // Some APIs use (abuse) void* for something like a user context,
diff --git a/clang/include/clang/Basic/DiagnosticSerialization.h b/clang/include/clang/Basic/DiagnosticSerialization.h
--- a/clang/include/clang/Basic/DiagnosticSerialization.h
+++ b/clang/include/clang/Basic/DiagnosticSerialization.h
@@ -15,7 +15,7 @@
 namespace diag {
 enum {
 #define DIAG(ENUM, FLAGS, DEFAULT_MAPPING, DESC, GROUP, SFINAE, NOWERROR,      \
-             SHOWINSYSHEADER, DEFERRABLE, CATEGORY)                            \
+             SHOWINSYSHEADER, SHOWINSYSMACRO, DEFERRABLE, CATEGORY)            \
   ENUM,
 #define SERIALIZATIONSTART
 #include "clang/Basic/DiagnosticSerializationKinds.inc"
diff --git a/clang/lib/Basic/DiagnosticIDs.cpp b/clang/lib/Basic/DiagnosticIDs.cpp
--- a/clang/lib/Basic/DiagnosticIDs.cpp
+++ b/clang/lib/Basic/DiagnosticIDs.cpp
@@ -33,7 +33,7 @@
 // platforms. See "How To Write Shared Libraries" by Ulrich Drepper.
 struct StaticDiagInfoDescriptionStringTable {
 #define DIAG(ENUM, CLASS, DEFAULT_SEVERITY, DESC, GROUP, SFINAE, NOWERROR,     \
-             SHOWINSYSHEADER, DEFERRABLE, CATEGORY)                            \
+             SHOWINSYSHEADER, SHOWINSYSMACRO, DEFERRABLE, CATEGORY)            \
   char ENUM##_desc[sizeof(DESC)];
   // clang-format off
 #include "clang/Basic/DiagnosticCommonKinds.inc"
@@ -54,7 +54,7 @@
 
 const StaticDiagInfoDescriptionStringTable StaticDiagInfoDescriptions = {
 #define DIAG(ENUM, CLASS, DEFAULT_SEVERITY, DESC, GROUP, SFINAE, NOWERROR,     \
-             SHOWINSYSHEADER, DEFERRABLE, CATEGORY)                            \
+             SHOWINSYSHEADER, SHOWINSYSMACRO, DEFERRABLE, CATEGORY)            \
   DESC,
 // clang-format off
 #include "clang/Basic/DiagnosticCommonKinds.inc"
@@ -79,7 +79,7 @@
 // StaticDiagInfoRec would have extra padding on 64-bit platforms.
 const uint32_t StaticDiagInfoDescriptionOffsets[] = {
 #define DIAG(ENUM, CLASS, DEFAULT_SEVERITY, DESC, GROUP, SFINAE, NOWERROR,     \
-             SHOWINSYSHEADER, DEFERRABLE, CATEGORY)                            \
+             SHOWINSYSHEADER, SHOWINSYSMACRO, DEFERRABLE, CATEGORY)            \
   offsetof(StaticDiagInfoDescriptionStringTable, ENUM##_desc),
 // clang-format off
 #include "clang/Basic/DiagnosticCommonKinds.inc"
@@ -115,6 +115,7 @@
   uint8_t Category : 6;
   uint8_t WarnNoWerror : 1;
   uint8_t WarnShowInSystemHeader : 1;
+  uint8_t WarnShowInSystemMacro : 1;
 
   uint16_t OptionGroupIndex : 15;
   uint16_t Deferrable : 1;
@@ -170,7 +171,7 @@
 const StaticDiagInfoRec StaticDiagInfo[] = {
 // clang-format off
 #define DIAG(ENUM, CLASS, DEFAULT_SEVERITY, DESC, GROUP, SFINAE, NOWERROR,     \
-             SHOWINSYSHEADER, DEFERRABLE, CATEGORY)                            \
+             SHOWINSYSHEADER, SHOWINSYSMACRO, DEFERRABLE, CATEGORY)            \
   {                                                                            \
       diag::ENUM,                                                              \
       DEFAULT_SEVERITY,                                                        \
@@ -179,6 +180,7 @@
       CATEGORY,                                                                \
       NOWERROR,                                                                \
       SHOWINSYSHEADER,                                                         \
+      SHOWINSYSMACRO,                                                          \
       GROUP,                                                                   \
 	    DEFERRABLE,                                                              \
       STR_SIZE(DESC, uint16_t)},
@@ -586,6 +588,13 @@
           Diag.getSourceManager().getExpansionLoc(Loc)))
     return diag::Severity::Ignored;
 
+  // We also ignore warnings due to system macros
+  bool ShowInSystemMacro =
+      !GetDiagInfo(DiagID) || GetDiagInfo(DiagID)->WarnShowInSystemMacro;
+  if (State->SuppressSystemWarnings && !ShowInSystemMacro && Loc.isValid() &&
+      Diag.getSourceManager().isInSystemMacro(Loc))
+    return diag::Severity::Ignored;
+
   return Result;
 }
 
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -7798,8 +7798,6 @@
   DeclarationName Name = R.getLookupName();
 
   // Emit warning and note.
-  if (getSourceManager().isInSystemMacro(R.getNameLoc()))
-    return;
   ShadowedDeclKind Kind = computeShadowedDeclKind(ShadowedDecl, OldDC);
   Diag(R.getNameLoc(), WarningDiag) << Name << Kind << OldDC;
   if (!CaptureLoc.isInvalid())
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -7727,8 +7727,7 @@
     CastExpr = Result.get();
   }
 
-  if (getLangOpts().CPlusPlus && !castType->isVoidType() &&
-      !getSourceManager().isInSystemMacro(LParenLoc))
+  if (getLangOpts().CPlusPlus && !castType->isVoidType())
     Diag(LParenLoc, diag::warn_old_style_cast) << CastExpr->getSourceRange();
 
   CheckTollFreeBridgeCast(castType, CastExpr);
diff --git a/clang/test/SemaCXX/warn-sysheader-macro.cpp b/clang/test/SemaCXX/warn-sysheader-macro.cpp
--- a/clang/test/SemaCXX/warn-sysheader-macro.cpp
+++ b/clang/test/SemaCXX/warn-sysheader-macro.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -verify -fsyntax-only -Wshadow -Wold-style-cast %s
+// RUN: %clang_cc1 -verify -fsyntax-only -Wshadow -Wold-style-cast -Wc++20-designator %s
 
 // Test that macro expansions from system headers don't trigger 'syntactic'
 // warnings that are not actionable.
@@ -12,6 +12,11 @@
 
 #define OLD_STYLE_CAST(a) ((int) (a))
 
+struct Foo {
+  int x;
+};
+#define DESIGNATED_INITIALIZERS (Foo{.x = 123})
+
 #else
 
 #define IS_SYSHEADER
@@ -28,8 +33,13 @@
 }
 
 void PR18147() {
-  // no -Wold_style_cast in system macro expansion
+  // no -Wold-style-cast in system macro expansion
   int i = OLD_STYLE_CAST(0);
 }
 
+void PR52944() {
+  // no -Wc++20-designator in system macro expansion
+  auto i = DESIGNATED_INITIALIZERS;
+}
+
 #endif
diff --git a/clang/test/TableGen/DiagnosticBase.inc b/clang/test/TableGen/DiagnosticBase.inc
--- a/clang/test/TableGen/DiagnosticBase.inc
+++ b/clang/test/TableGen/DiagnosticBase.inc
@@ -76,6 +76,7 @@
   bit            AccessControl = 0;
   bit            WarningNoWerror = 0;
   bit            ShowInSystemHeader = 0;
+  bit            ShowInSystemMacro = 1;
   bit            Deferrable = 0;
   Severity       DefaultSeverity = defaultmapping;
   DiagGroup      Group;
@@ -100,6 +101,14 @@
   bit ShowInSystemHeader = 0;
 }
 
+class ShowInSystemMacro {
+  bit ShowInSystemMacro = 1;
+}
+
+class SuppressInSystemMacro {
+  bit ShowInSystemMacro = 0;
+}
+
 class Deferrable {
   bit Deferrable = 1;
 }
diff --git a/clang/test/TableGen/deferred-diag.td b/clang/test/TableGen/deferred-diag.td
--- a/clang/test/TableGen/deferred-diag.td
+++ b/clang/test/TableGen/deferred-diag.td
@@ -5,23 +5,23 @@
 // Test usage of Deferrable and NonDeferrable in diagnostics.
 
 def test_default : Error<"This error is non-deferrable by default">;
-// CHECK-DAG: DIAG(test_default, {{.*}}SFINAE_SubstitutionFailure, false, true, false, 0)
+// CHECK-DAG: DIAG(test_default, {{.*}}SFINAE_SubstitutionFailure, false, true, true, false, 0)
 
 def test_deferrable : Error<"This error is deferrable">, Deferrable;
-// CHECK-DAG: DIAG(test_deferrable, {{.*}} SFINAE_SubstitutionFailure, false, true, true, 0)
+// CHECK-DAG: DIAG(test_deferrable, {{.*}} SFINAE_SubstitutionFailure, false, true, true, true, 0)
 
 def test_non_deferrable : Error<"This error is non-deferrable">, NonDeferrable;
-// CHECK-DAG: DIAG(test_non_deferrable, {{.*}} SFINAE_SubstitutionFailure, false, true, false, 0)
+// CHECK-DAG: DIAG(test_non_deferrable, {{.*}} SFINAE_SubstitutionFailure, false, true, true, false, 0)
 
 let Deferrable = 1 in {
 
 def test_let : Error<"This error is deferrable by let">;
-// CHECK-DAG: DIAG(test_let, {{.*}} SFINAE_SubstitutionFailure, false, true, true, 0)
+// CHECK-DAG: DIAG(test_let, {{.*}} SFINAE_SubstitutionFailure, false, true, true, true, 0)
 
 // Make sure TextSubstitution is allowed in the let Deferrable block.
 def textsub : TextSubstitution<"%select{text1|text2}0">;
 
 def test_let2 : Error<"This error is deferrable by let %sub{textsub}0">;
-// CHECK-DAG: DIAG(test_let2, {{.*}} SFINAE_SubstitutionFailure, false, true, true, 0)
+// CHECK-DAG: DIAG(test_let2, {{.*}} SFINAE_SubstitutionFailure, false, true, true, true, 0)
 
-}
\ No newline at end of file
+}
diff --git a/clang/tools/diagtool/DiagnosticNames.cpp b/clang/tools/diagtool/DiagnosticNames.cpp
--- a/clang/tools/diagtool/DiagnosticNames.cpp
+++ b/clang/tools/diagtool/DiagnosticNames.cpp
@@ -27,9 +27,9 @@
 // FIXME: Is it worth having two tables, especially when this one can get
 // out of sync easily?
 static const DiagnosticRecord BuiltinDiagnosticsByID[] = {
-#define DIAG(ENUM,CLASS,DEFAULT_MAPPING,DESC,GROUP,               \
-             SFINAE,NOWERROR,SHOWINSYSHEADER,DEFER,CATEGORY)            \
-  { #ENUM, diag::ENUM, STR_SIZE(#ENUM, uint8_t) },
+#define DIAG(ENUM, CLASS, DEFAULT_MAPPING, DESC, GROUP, SFINAE, NOWERROR,      \
+             SHOWINSYSHEADER, SHOWINSYSMACRO, DEFER, CATEGORY)                 \
+  {#ENUM, diag::ENUM, STR_SIZE(#ENUM, uint8_t)},
 #include "clang/Basic/DiagnosticCommonKinds.inc"
 #include "clang/Basic/DiagnosticCrossTUKinds.inc"
 #include "clang/Basic/DiagnosticDriverKinds.inc"
diff --git a/clang/utils/TableGen/ClangDiagnosticsEmitter.cpp b/clang/utils/TableGen/ClangDiagnosticsEmitter.cpp
--- a/clang/utils/TableGen/ClangDiagnosticsEmitter.cpp
+++ b/clang/utils/TableGen/ClangDiagnosticsEmitter.cpp
@@ -1311,6 +1311,11 @@
     else
       OS << ", false";
 
+    if (R.getValueAsBit("ShowInSystemMacro"))
+      OS << ", true";
+    else
+      OS << ", false";
+
     if (R.getValueAsBit("Deferrable"))
       OS << ", true";
     else