Rename FunctionProtoType accessors from 'arguments' to 'parameters'

Fix a perennial source of confusion in the clang type system: Declarations and
function prototypes have parameters to which arguments are supplied, so calling
these 'arguments' was a stretch even in C mode, let alone C++ where default
arguments, templates and overloading make the distinction important to get
right.

Readability win across the board, especially in the casting, ADL and
overloading implementations which make a lot more sense at a glance now.

Will keep an eye on the builders and update dependent projects shortly.

No functional change.

llvm-svn: 199686
diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index 7a1cd71..4d864f2 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -2308,7 +2308,8 @@
     return false;
 
   const FunctionProtoType *proto = getType()->castAs<FunctionProtoType>();
-  if (proto->getNumArgs() != 2 || proto->isVariadic()) return false;
+  if (proto->getNumParams() != 2 || proto->isVariadic())
+    return false;
 
   ASTContext &Context =
     cast<TranslationUnitDecl>(getDeclContext()->getRedeclContext())
@@ -2316,7 +2317,7 @@
 
   // The result type and first argument type are constant across all
   // these operators.  The second argument must be exactly void*.
-  return (proto->getArgType(1).getCanonicalType() == Context.VoidPtrTy);
+  return (proto->getParamType(1).getCanonicalType() == Context.VoidPtrTy);
 }
 
 static bool isNamespaceStd(const DeclContext *DC) {
@@ -2342,17 +2343,17 @@
     return false;
 
   const FunctionProtoType *FPT = getType()->castAs<FunctionProtoType>();
-  if (FPT->getNumArgs() > 2 || FPT->isVariadic())
+  if (FPT->getNumParams() > 2 || FPT->isVariadic())
     return false;
 
   // If this is a single-parameter function, it must be a replaceable global
   // allocation or deallocation function.
-  if (FPT->getNumArgs() == 1)
+  if (FPT->getNumParams() == 1)
     return true;
 
   // Otherwise, we're looking for a second parameter whose type is
   // 'const std::nothrow_t &', or, in C++1y, 'std::size_t'.
-  QualType Ty = FPT->getArgType(1);
+  QualType Ty = FPT->getParamType(1);
   ASTContext &Ctx = getASTContext();
   if (Ctx.getLangOpts().SizedDeallocation &&
       Ctx.hasSameType(Ty, Ctx.getSizeType()))
@@ -2385,7 +2386,7 @@
     return 0;
 
   if (getNumParams() != 2 || isVariadic() ||
-      !Ctx.hasSameType(getType()->castAs<FunctionProtoType>()->getArgType(1),
+      !Ctx.hasSameType(getType()->castAs<FunctionProtoType>()->getParamType(1),
                        Ctx.getSizeType()))
     return 0;
 
@@ -2517,7 +2518,7 @@
 /// after it has been created.
 unsigned FunctionDecl::getNumParams() const {
   const FunctionProtoType *FPT = getType()->getAs<FunctionProtoType>();
-  return FPT ? FPT->getNumArgs() : 0;
+  return FPT ? FPT->getNumParams() : 0;
 }
 
 void FunctionDecl::setParams(ASTContext &C,