[Sema] Mark implicitly-inserted ICE's as being part of explicit cast (PR38166)

Summary:
As discussed in [[ https://bugs.llvm.org/show_bug.cgi?id=38166 | PR38166 ]], we need to be able to distinqush whether the cast
we are visiting is actually a cast, or part of an `ExplicitCast`.
There are at least four ways to get there:
1. Introduce a new `CastKind`, and use it instead of `IntegralCast` if we are in `ExplicitCast`.

   Would work, but does not scale - what if we will need more of these cast kinds?
2. Introduce a flag in `CastExprBits`, whether this cast is part of `ExplicitCast` or not.

   Would work, but it isn't immediately clear where it needs to be set.
2. Fix `ScalarExprEmitter::VisitCastExpr()` to visit these `NoOp` casts.

   As pointed out by @rsmith, CodeGenFunction::EmitMaterializeTemporaryExpr calls

   skipRValueSubobjectAdjustments, which steps over the CK_NoOp cast`,

   which explains why we currently don't visit those.

   This is probably impossible, as @efriedma points out, that is intentional as per `[class.temporary]` in the standard
3. And the simplest one, just record which NoOp casts we skip.

   It just kinda works as-is afterwards.

But, the approach with a flag is the least intrusive one, and is probably the best one overall.

Reviewers: rsmith, rjmccall, majnemer, efriedma

Reviewed By: rsmith

Subscribers: cfe-commits, aaron.ballman, vsk, llvm-commits, rsmith

Differential Revision: https://reviews.llvm.org/D49508

llvm-svn: 337815

1 files changed, 3 insertions, 0 deletions

diff --git a/clang/lib/AST/ASTDumper.cpp b/clang/lib/AST/ASTDumper.cpp
index 6d9f24020fe..6ccd913bd3e 100644
--- a/clang/lib/AST/ASTDumper.cpp
+++ b/clang/lib/AST/ASTDumper.cpp
@@ -2117,6 +2117,9 @@ void ASTDumper::VisitCastExpr(const CastExpr *Node) {
   }
   dumpBasePath(OS, Node);
   OS << ">";
+
+  if (Node->getIsPartOfExplicitCast())
+    OS << " part_of_explicit_cast";
 }
 
 void ASTDumper::VisitDeclRefExpr(const DeclRefExpr *Node) {