[clang] Use TargetInfo to decide Mangling for C (#129920)

Instead of hardcoding the decision on what mangling scheme to use based
on targets, use TargetInfo to make the decision.

Author: Prabhuk

clang/include/clang/Basic/TargetInfo.h

@@ -253,6 +253,7 @@ class TargetInfo : public TransferrableTargetInfo,
   const char *MCountName;
   unsigned char RegParmMax, SSERegParmMax;
   TargetCXXABI TheCXXABI;
+  bool UseMicrosoftManglingForC = false;
   const LangASMap *AddrSpaceMap;
 
   mutable StringRef PlatformName;
@@ -1344,6 +1345,11 @@ class TargetInfo : public TransferrableTargetInfo,
     return TheCXXABI;
   }
 
+  /// Should the Microsoft mangling scheme be used for C Calling Convention.
+  bool shouldUseMicrosoftCCforMangling() const {
+    return UseMicrosoftManglingForC;
+  }
+
   /// Target the specified CPU.
   ///
   /// \return  False on error (invalid CPU name).

clang/lib/AST/Mangle.cpp

@@ -74,7 +74,7 @@ static CCMangling getCallingConvMangling(const ASTContext &Context,
       if (FD->isMain() && FD->getNumParams() == 2)
         return CCM_WasmMainArgcArgv;
 
-  if (!Triple.isOSWindows() || !Triple.isX86())
+  if (!TI.shouldUseMicrosoftCCforMangling())
     return CCM_Other;
 
   if (Context.getLangOpts().CPlusPlus && !isExternC(ND) &&

clang/lib/Basic/Targets/OSTargets.h

@@ -817,6 +817,7 @@ class LLVM_LIBRARY_VISIBILITY UEFITargetInfo : public OSTargetInfo<Target> {
       : OSTargetInfo<Target>(Triple, Opts) {
     this->WCharType = TargetInfo::UnsignedShort;
     this->WIntType = TargetInfo::UnsignedShort;
+    this->UseMicrosoftManglingForC = true;
   }
 };
 
@@ -837,6 +838,7 @@ class LLVM_LIBRARY_VISIBILITY WindowsTargetInfo : public OSTargetInfo<Target> {
       : OSTargetInfo<Target>(Triple, Opts) {
     this->WCharType = TargetInfo::UnsignedShort;
     this->WIntType = TargetInfo::UnsignedShort;
+    this->UseMicrosoftManglingForC = true;
   }
 };
 

clang/lib/Sema/SemaExpr.cpp

@@ -17978,10 +17978,9 @@ static bool isPotentiallyConstantEvaluatedContext(Sema &SemaRef) {
 /// Return true if this function has a calling convention that requires mangling
 /// in the size of the parameter pack.
 static bool funcHasParameterSizeMangling(Sema &S, FunctionDecl *FD) {
-  // These manglings don't do anything on non-Windows or non-x86 platforms, so
-  // we don't need parameter type sizes.
-  const llvm::Triple &TT = S.Context.getTargetInfo().getTriple();
-  if (!TT.isOSWindows() || !TT.isX86())
+  // These manglings are only applicable for targets whcih use Microsoft
+  // mangling scheme for C.
+  if (!S.Context.getTargetInfo().shouldUseMicrosoftCCforMangling())
     return false;
 
   // If this is C++ and this isn't an extern "C" function, parameters do not