[Clang] Make the SizeType, SignedSizeType and PtrdiffType be named sugar types instead of built-in types (#143653)

Including the results of `sizeof`, `sizeof...`, `__datasizeof`,
`__alignof`, `_Alignof`, `alignof`, `_Countof`, `size_t` literals, and
signed `size_t` literals, the results of pointer-pointer subtraction and
checks for standard library functions (and their calls).

The goal is to enable clang and downstream tools such as clangd and
clang-tidy to provide more portable hints and diagnostics.

The previous discussion can be found at #136542.

This PR implements this feature by introducing a new subtype of `Type`
called `PredefinedSugarType`, which was considered appropriate in
discussions. I tried to keep `PredefinedSugarType` simple enough yet not
limited to `size_t` and `ptrdiff_t` so that it can be used for other
purposes. `PredefinedSugarType` wraps a canonical `Type` and provides a
name, conceptually similar to a compiler internal `TypedefType` but
without depending on a `TypedefDecl` or a source file.

Additionally, checks for the `z` and `t` format specifiers in format
strings for `scanf` and `printf` were added. It will precisely match
expressions using `typedef`s or built-in expressions.

The affected tests indicates that it works very well.

Several code require that `SizeType` is canonical, so I kept `SizeType`
to its canonical form.

The failed tests in CI are allowed to fail. See the
[comment](https://github.com/llvm/llvm-project/pull/135386#issuecomment-3049426611)
in another PR #135386.

1 files changed, 2 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index 0fda31c..ab345a5 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -720,7 +720,7 @@ static bool matchesStlAllocatorFn(const Decl *D, const ASTContext &Ctx) {
       (MD->getNumParams() != 1 && MD->getNumParams() != 2))
     return false;
 
-  if (MD->parameters()[0]->getType().getCanonicalType() != Ctx.getSizeType())
+  if (!Ctx.hasSameType(MD->parameters()[0]->getType(), Ctx.getSizeType()))
     return false;
 
   if (MD->getNumParams() == 2) {
@@ -2491,6 +2491,7 @@ void CodeGenFunction::EmitVariablyModifiedType(QualType type) {
     case Type::ObjCObjectPointer:
     case Type::BitInt:
     case Type::HLSLInlineSpirv:
+    case Type::PredefinedSugar:
       llvm_unreachable("type class is never variably-modified!");
 
     case Type::Elaborated: