diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index 5456b2a8fb922..76cc2ba0d0eb4 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -474,11 +474,9 @@ void CompilerInstance::createPreprocessor(TranslationUnitKind TUKind) {
   InitializeFileRemapping(PP->getDiagnostics(), PP->getSourceManager(),
                           PP->getFileManager(), PPOpts);
 
-  if (getFrontendOpts().CASIncludeTreeID.empty()) {
-    // Predefine macros and configure the preprocessor.
-    InitializePreprocessor(*PP, PPOpts, getPCHContainerReader(),
-                           getFrontendOpts());
-  }
+  // Predefine macros and configure the preprocessor.
+  InitializePreprocessor(*PP, PPOpts, getPCHContainerReader(),
+                         getFrontendOpts());
 
   // Initialize the header search object.  In CUDA compilations, we use the aux
   // triple (the host triple) to initialize our header search, since we need to
diff --git a/clang/lib/Tooling/DependencyScanning/DependencyScanningTool.cpp b/clang/lib/Tooling/DependencyScanning/DependencyScanningTool.cpp
index 6f2f25b51a85f..a832c0e63416a 100644
--- a/clang/lib/Tooling/DependencyScanning/DependencyScanningTool.cpp
+++ b/clang/lib/Tooling/DependencyScanning/DependencyScanningTool.cpp
@@ -302,9 +302,11 @@ void IncludeTreePPConsumer::handleHasIncludeCheck(Preprocessor &PP,
 void IncludeTreePPConsumer::finalize(CompilerInstance &CI) {
   FileManager &FM = CI.getFileManager();
 
-  auto addFile = [&](StringRef FilePath) -> bool {
+  auto addFile = [&](StringRef FilePath, bool IgnoreFileError = false) -> bool {
     llvm::ErrorOr<const FileEntry *> FE = FM.getFile(FilePath);
     if (!FE) {
+      if (IgnoreFileError)
+        return true;
       ErrorToReport = llvm::errorCodeToError(FE.getError());
       return false;
     }
@@ -321,6 +323,15 @@ void IncludeTreePPConsumer::finalize(CompilerInstance &CI) {
       return;
   }
 
+  StringRef Sysroot = CI.getHeaderSearchOpts().Sysroot;
+  if (!Sysroot.empty()) {
+    // Include 'SDKSettings.json', if it exists, to accomodate availability
+    // checks during the compilation.
+    llvm::SmallString<256> FilePath = Sysroot;
+    llvm::sys::path::append(FilePath, "SDKSettings.json");
+    addFile(FilePath, /*IgnoreFileError*/ true);
+  }
+
   PreprocessorOptions &PPOpts = CI.getPreprocessorOpts();
   if (PPOpts.ImplicitPCHInclude.empty())
     return; // no need for additional work.
diff --git a/clang/lib/Tooling/DependencyScanning/ScanAndUpdateArgs.cpp b/clang/lib/Tooling/DependencyScanning/ScanAndUpdateArgs.cpp
index 50542c7c4f667..e596f99a0a46b 100644
--- a/clang/lib/Tooling/DependencyScanning/ScanAndUpdateArgs.cpp
+++ b/clang/lib/Tooling/DependencyScanning/ScanAndUpdateArgs.cpp
@@ -85,7 +85,11 @@ static void updateCompilerInvocation(CompilerInvocation &Invocation,
   if (ProduceIncludeTree) {
     Invocation.getFrontendOpts().CASIncludeTreeID = RootID;
     Invocation.getFrontendOpts().Inputs.clear();
+    // Preserve sysroot path to accommodate lookup for 'SDKSettings.json' during
+    // availability checking.
+    std::string OriginalSysroot = Invocation.getHeaderSearchOpts().Sysroot;
     Invocation.getHeaderSearchOpts() = HeaderSearchOptions();
+    Invocation.getHeaderSearchOpts().Sysroot = OriginalSysroot;
     auto &PPOpts = Invocation.getPreprocessorOpts();
     // We don't need this because we save the contents of the PCH file in the
     // include tree root.
diff --git a/clang/test/CAS/Inputs/MacOSX11.0.sdk/SDKSettings.json b/clang/test/CAS/Inputs/MacOSX11.0.sdk/SDKSettings.json
new file mode 100644
index 0000000000000..b40e35e882e60
--- /dev/null
+++ b/clang/test/CAS/Inputs/MacOSX11.0.sdk/SDKSettings.json
@@ -0,0 +1,23 @@
+{
+  "DefaultVariant": "macos", "DisplayName": "macOS 11",
+  "Version": "11.0",
+  "MaximumDeploymentTarget": "11.0.99",
+  "PropertyConditionFallbackNames": [], "VersionMap": {
+    "iOSMac_macOS": {
+      "13.2": "10.15.1",
+      "13.4": "10.15.4",
+      "13.3.1": "10.15.3",
+      "13.3": "10.15.2",
+      "13.1": "10.15",
+      "14.0": "11.0"
+    },
+    "macOS_iOSMac": {
+      "10.15.2": "13.3",
+      "11.0": "14.0",
+      "10.15": "13.1",
+      "10.15.3": "13.3.1",
+      "10.15.1": "13.2",
+      "10.15.4": "13.4"
+    }
+  }
+}
diff --git a/clang/test/CAS/availability-check.c b/clang/test/CAS/availability-check.c
new file mode 100644
index 0000000000000..ac55bf485ddd3
--- /dev/null
+++ b/clang/test/CAS/availability-check.c
@@ -0,0 +1,17 @@
+// RUN: rm -rf %t && mkdir %t
+
+// RUN: %clang_cc1 -triple x86_64-apple-ios14-macabi -isysroot %S/Inputs/MacOSX11.0.sdk -fsyntax-only -verify %s
+
+// RUN: %clang -cc1depscan -o %t/cmd.rsp -fdepscan=inline -fdepscan-include-tree -cc1-args \
+// RUN:     -cc1 -fcas-path %t/cas -triple x86_64-apple-ios14-macabi -isysroot %S/Inputs/MacOSX11.0.sdk %s
+
+// FIXME: `-verify` should work with a CAS invocation.
+// RUN: not %clang @%t/cmd.rsp -fsyntax-only 2> %t/out.txt
+// RUN: FileCheck -input-file %t/out.txt %s
+// CHECK: error: 'fUnavail' is unavailable
+
+void fUnavail(void) __attribute__((availability(macOS, obsoleted = 10.15))); // expected-note {{marked unavailable here}}
+
+void test() {
+  fUnavail(); // expected-error {{unavailable}}
+}
diff --git a/clang/test/CAS/depscan-include-tree.c b/clang/test/CAS/depscan-include-tree.c
index b163d07c69602..71d8ab87a4dcd 100644
--- a/clang/test/CAS/depscan-include-tree.c
+++ b/clang/test/CAS/depscan-include-tree.c
@@ -11,9 +11,9 @@
 
 // CHECK: "-fcas-path" "[[PREFIX]]/cas"
 // CHECK: "-fcas-include-tree"
+// CHECK: "-isysroot"
 // SHOULD-NOT: "-fcas-fs"
 // SHOULD-NOT: "-fcas-fs-working-directory"
-// SHOULD-NOT: "-isysroot"
 // SHOULD-NOT: "-I"
 // SHOULD-NOT: "[[PREFIX]]/t.c"
 // SHOULD-NOT: "-D"
diff --git a/clang/test/ClangScanDeps/include-tree-with-pch.c b/clang/test/ClangScanDeps/include-tree-with-pch.c
index 3fec4e4116553..416bbfd60668e 100644
--- a/clang/test/ClangScanDeps/include-tree-with-pch.c
+++ b/clang/test/ClangScanDeps/include-tree-with-pch.c
@@ -2,7 +2,7 @@
 // RUN: split-file %s %t
 // RUN: sed -e "s|DIR|%/t|g" %t/cdb.json.template > %t/cdb.json
 
-// RUN: %clang -x c-header %t/prefix.h -o %t/prefix.pch -fdepscan=inline -fdepscan-include-tree -Xclang -fcas-path -Xclang %t/cas
+// RUN: %clang -x c-header %t/prefix.h -target x86_64-apple-macos12 -o %t/prefix.pch -fdepscan=inline -fdepscan-include-tree -Xclang -fcas-path -Xclang %t/cas
 // RUN: clang-scan-deps -compilation-database %t/cdb.json -format experimental-include-tree -cas-path %t/cas > %t/result.txt
 // RUN: FileCheck %s -input-file %t/result.txt -DPREFIX=%/t
 
@@ -43,7 +43,7 @@ int n3 = 0;
 //--- cdb.json.template
 [{
   "directory" : "DIR",
-  "command" : "clang -fsyntax-only DIR/t.c -Xclang -include-pch -Xclang DIR/prefix.pch",
+  "command" : "clang -fsyntax-only DIR/t.c -target x86_64-apple-macos12 -isysroot DIR -Xclang -include-pch -Xclang DIR/prefix.pch",
   "file" : "DIR/t.c"
 }]