[clang][X86] Only define __CET__ macro for X86 targets (#127616)

The `-fcf-protection` flag is now also used to enable CFI features for
the RISC-V target, so it's not suitable to define `__CET__` solely based
on the flag anymore. This patch moves the definition of the `__CET__`
macro into X86 target hook, so only X86 targets with the
`-fcf-protection` flag would enable the `__CET__` macro.

See #109784 and
#112477 for the adoption
of `-fcf-protection` flag for RISC-V targets.

Author: mylai-mtk

clang/lib/Basic/Targets/X86.cpp

@@ -1109,6 +1109,10 @@ void X86TargetInfo::getTargetDefines(const LangOptions &Opts,
 
   if (HasFloat128)
     Builder.defineMacro("__SIZEOF_FLOAT128__", "16");
+
+  if (Opts.CFProtectionReturn || Opts.CFProtectionBranch)
+    Builder.defineMacro("__CET__", Twine{(Opts.CFProtectionReturn << 1) |
+                                         Opts.CFProtectionBranch});
 }
 
 bool X86TargetInfo::isValidFeatureName(StringRef Name) const {

clang/lib/Frontend/CompilerInvocation.cpp

@@ -4776,17 +4776,6 @@ static bool ParsePreprocessorArgs(PreprocessorOptions &Opts, ArgList &Args,
     }
   }
 
-  // Add the __CET__ macro if a CFProtection option is set.
-  if (const Arg *A = Args.getLastArg(OPT_fcf_protection_EQ)) {
-    StringRef Name = A->getValue();
-    if (Name == "branch")
-      Opts.addMacroDef("__CET__=1");
-    else if (Name == "return")
-      Opts.addMacroDef("__CET__=2");
-    else if (Name == "full")
-      Opts.addMacroDef("__CET__=3");
-  }
-
   // Add macros from the command line.
   for (const auto *A : Args.filtered(OPT_D, OPT_U)) {
     if (A->getOption().matches(OPT_D))

clang/test/Preprocessor/riscv-cf-protection-return.c

@@ -40,5 +40,7 @@
 // RUN: -menable-experimental-extensions -fcf-protection=full -E -dM %s -o - \
 // RUN: | FileCheck --check-prefixes=SHSTK-MACRO %s
 
+// SHSTK-MACRO-NOT: __CET__
 // SHSTK-MACRO: __riscv_shadow_stack 1{{$}}
+// SHSTK-MACRO-NOT: __CET__
 // NO-MACRO-NOT: __riscv_shadow_stack