[HLSL] Cleanup support for `this` as an l-value

The goal of this change is to clean up some of the code surrounding
HLSL using CXXThisExpr as a non-pointer l-value. This change cleans up
a bunch of assumptions and inconsistencies around how the type of
`this` is handled through the AST and code generation.

This change is be mostly NFC for HLSL, and completely NFC for other
language modes.

This change introduces a new member to query for the this object's type
and seeks to clarify the normal usages of the this type.

With the introudction of HLSL to clang, CXXThisExpr may now be an
l-value and behave like a reference type rather than C++'s normal
method of it being an r-value of pointer type.

With this change there are now three ways in which a caller might need
to query the type of `this`:

* The type of the `CXXThisExpr`
* The type of the object `this` referrs to
* The type of the implicit (or explicit) `this` argument

This change codifies those three ways you may need to query
respectively as:

* CXXMethodDecl::getThisType()
* CXXMethodDecl::getThisObjectType()
* CXXMethodDecl::getThisArgType()

This change then revisits all uses of `getThisType()`, and in cases
where the only use was to resolve the pointee type, it replaces the
call with `getThisObjectType()`. In other cases it evaluates whether
the desired returned type is the type of the `this` expr, or the type
of the `this` function argument. The `this` expr type is used for
creating additional expr AST nodes and for member lookup, while the
argument type is used mostly for code generation.

Additionally some cases that used `getThisType` in simple queries could
be substituted for `getThisObjectType`. Since `getThisType` is
implemented in terms of `getThisObjectType` calling the later should be
more efficient if the former isn't needed.

Reviewed By: aaron.ballman, bogner

Differential Revision: https://reviews.llvm.org/D159247

1 files changed, 5 insertions, 14 deletions

diff --git a/clang/lib/Sema/SemaExprMember.cpp b/clang/lib/Sema/SemaExprMember.cpp
index 3d14ca3..fe92215 100644
--- a/clang/lib/Sema/SemaExprMember.cpp
+++ b/clang/lib/Sema/SemaExprMember.cpp
@@ -1897,20 +1897,11 @@ Sema::BuildImplicitMemberExpr(const CXXScopeSpec &SS,
     if (SS.getRange().isValid())
       Loc = SS.getRange().getBegin();
     baseExpr = BuildCXXThisExpr(loc, ThisTy, /*IsImplicit=*/true);
-    if (getLangOpts().HLSL && ThisTy.getTypePtr()->isPointerType()) {
-      ThisTy = ThisTy.getTypePtr()->getPointeeType();
-      return BuildMemberReferenceExpr(baseExpr, ThisTy,
-                                      /*OpLoc*/ SourceLocation(),
-                                      /*IsArrow*/ false, SS, TemplateKWLoc,
-                                      /*FirstQualifierInScope*/ nullptr, R,
-                                      TemplateArgs, S);
-    }
   }
 
-  return BuildMemberReferenceExpr(baseExpr, ThisTy,
-                                  /*OpLoc*/ SourceLocation(),
-                                  /*IsArrow*/ true,
-                                  SS, TemplateKWLoc,
-                                  /*FirstQualifierInScope*/ nullptr,
-                                  R, TemplateArgs, S);
+  return BuildMemberReferenceExpr(
+      baseExpr, ThisTy,
+      /*OpLoc=*/SourceLocation(),
+      /*IsArrow=*/!getLangOpts().HLSL, SS, TemplateKWLoc,
+      /*FirstQualifierInScope=*/nullptr, R, TemplateArgs, S);
 }