[AST] Update the comments of the various Expr::Ignore* + Related cleanups

The description of what the various Expr::Ignore* do has drifted from the
actual implementation.

Inspection reveals that IgnoreParenImpCasts() is not equivalent to doing
IgnoreParens() + IgnoreImpCasts() until reaching a fixed point, but
IgnoreParenCasts() is equivalent to doing IgnoreParens() + IgnoreCasts()
until reaching a fixed point. There is also a fair amount of duplication
in the various Expr::Ignore* functions which increase the chance of further
future inconsistencies. In preparation for the next patch which will factor
out the implementation of the various Expr::Ignore*, do the following cleanups:

Remove Stmt::IgnoreImplicit, in favor of Expr::IgnoreImplicit. IgnoreImplicit
is the only function among all of the Expr::Ignore* which is available in Stmt.
There are only a few users of Stmt::IgnoreImplicit. They can just use instead
Expr::IgnoreImplicit like they have to do for the other Ignore*.

Move Expr::IgnoreImpCasts() from Expr.h to Expr.cpp. This made no difference
in the run-time with my usual benchmark (-fsyntax-only on all of Boost).

While we are at it, make IgnoreParenNoopCasts take a const reference to the
ASTContext for const correctness.

Update the comments to match what the Expr::Ignore* are actually doing.
I am not sure that listing exactly what each Expr::Ignore* do is optimal,
but it certainly looks better than the current state which is in my opinion
between misleading and just plain wrong.

The whole patch is NFC (if you count removing Stmt::IgnoreImplicit as NFC).

Differential Revision: https://reviews.llvm.org/D57266

Reviewed By: aaron.ballman

llvm-svn: 353006

1 files changed, 4 insertions, 4 deletions

diff --git a/clang/lib/ARCMigrate/TransRetainReleaseDealloc.cpp b/clang/lib/ARCMigrate/TransRetainReleaseDealloc.cpp
index 347c198f68f..b76fc65574d 100644
--- a/clang/lib/ARCMigrate/TransRetainReleaseDealloc.cpp
+++ b/clang/lib/ARCMigrate/TransRetainReleaseDealloc.cpp
@@ -269,8 +269,8 @@ private:
 
     if (prevChildS != childE) {
       prevStmt = *prevChildS;
-      if (prevStmt)
-        prevStmt = prevStmt->IgnoreImplicit();
+      if (auto *E = dyn_cast_or_null<Expr>(prevStmt))
+        prevStmt = E->IgnoreImplicit();
     }
 
     if (currChildS == childE)
@@ -280,8 +280,8 @@ private:
       return std::make_pair(prevStmt, nextStmt);
 
     nextStmt = *currChildS;
-    if (nextStmt)
-      nextStmt = nextStmt->IgnoreImplicit();
+    if (auto *E = dyn_cast_or_null<Expr>(nextStmt))
+      nextStmt = E->IgnoreImplicit();
 
     return std::make_pair(prevStmt, nextStmt);
   }