Ignore ConstantExpr in IgnoreParens

Summary:
This moves it up from IgnoreParenImpCasts to IgnoreParens, so that more
helpers ignore it. For most clients, this ensures that these helpers
behave the same with and without C++17 enabled, which is what appears to
introduce these new expression nodes.

Fixes PR39881

Reviewers: void, rsmith

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D55853

llvm-svn: 350068
diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index 11191c4..6aa1199 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -2596,6 +2596,10 @@
         continue;
       }
     }
+    if (ConstantExpr *CE = dyn_cast<ConstantExpr>(E)) {
+      E = CE->getSubExpr();
+      continue;
+    }
     return E;
   }
 }
@@ -2718,10 +2722,6 @@
       E = NTTP->getReplacement();
       continue;
     }
-    if (ConstantExpr *CE = dyn_cast<ConstantExpr>(E)) {
-      E = CE->getSubExpr();
-      continue;
-    }
     return E;
   }
 }