[clang][PP] Add extension to predefine target OS macros (#74676)

Add an extension feature `define-target-os-macros` that enables clang to
provide definitions of common TARGET_OS_* conditional macros. The
extension is enabled in the Darwin toolchain driver.

4 files changed, 23 insertions, 0 deletions

diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index f02f7c84..eb26bfad 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -1294,6 +1294,9 @@ void Clang::AddPreprocessingOptions(Compilation &C, const JobAction &JA,
     CmdArgs.push_back("-source-date-epoch");
     CmdArgs.push_back(Args.MakeArgString(Epoch));
   }
+
+  Args.addOptInFlag(CmdArgs, options::OPT_fdefine_target_os_macros,
+                    options::OPT_fno_define_target_os_macros);
 }
 
 // FIXME: Move to target hook.
diff --git a/clang/lib/Driver/ToolChains/Darwin.cpp b/clang/lib/Driver/ToolChains/Darwin.cpp
index f09bc27..d3005d6 100644
--- a/clang/lib/Driver/ToolChains/Darwin.cpp
+++ b/clang/lib/Driver/ToolChains/Darwin.cpp
@@ -2916,6 +2916,10 @@ void Darwin::addClangTargetOptions(const llvm::opt::ArgList &DriverArgs,
   // to fix the same problem with C++ headers, and is generally fragile.
   if (!sdkSupportsBuiltinModules(TargetPlatform, SDKInfo))
     CC1Args.push_back("-fbuiltin-headers-in-system-modules");
+
+  if (!DriverArgs.hasArgNoClaim(options::OPT_fdefine_target_os_macros,
+                                options::OPT_fno_define_target_os_macros))
+    CC1Args.push_back("-fdefine-target-os-macros");
 }
 
 void Darwin::addClangCC1ASTargetOptions(
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 56de0f7..b33bdad 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -4365,6 +4365,9 @@ static void GeneratePreprocessorArgs(const PreprocessorOptions &Opts,
   if (Opts.SourceDateEpoch)
     GenerateArg(Consumer, OPT_source_date_epoch, Twine(*Opts.SourceDateEpoch));
 
+  if (Opts.DefineTargetOSMacros)
+    GenerateArg(Consumer, OPT_fdefine_target_os_macros);
+
   // Don't handle LexEditorPlaceholders. It is implied by the action that is
   // generated elsewhere.
 }
@@ -4463,6 +4466,10 @@ static bool ParsePreprocessorArgs(PreprocessorOptions &Opts, ArgList &Args,
   if (isStrictlyPreprocessorAction(Action))
     Opts.LexEditorPlaceholders = false;
 
+  Opts.DefineTargetOSMacros =
+      Args.hasFlag(OPT_fdefine_target_os_macros,
+                   OPT_fno_define_target_os_macros, Opts.DefineTargetOSMacros);
+
   return Diags.getNumErrors() == NumErrorsBefore;
 }
 
diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index 16a2947..d83128a 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -1351,6 +1351,15 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
   if (TI.getTriple().isOSBinFormatELF())
     Builder.defineMacro("__ELF__");
 
+  // Target OS macro definitions.
+  if (PPOpts.DefineTargetOSMacros) {
+    const llvm::Triple &Triple = TI.getTriple();
+#define TARGET_OS(Name, Predicate)                                             \
+  Builder.defineMacro(#Name, (Predicate) ? "1" : "0");
+#include "clang/Basic/TargetOSMacros.def"
+#undef TARGET_OS
+  }
+
   // Get other target #defines.
   TI.getTargetDefines(LangOpts, Builder);
 }