[Preprocessor] Don't avoid entering included files after hitting a fatal error.

Change in r337953 violated the contract for `CXTranslationUnit_KeepGoing`:

> Do not stop processing when fatal errors are encountered.

Use different approach to fix long processing times with multiple inclusion
cycles. Instead of stopping preprocessing for fatal errors, do this after
reaching the max allowed include depth and only for the files that were
processed already. It is likely but not guaranteed those files cause a cycle.

rdar://problem/46108547

Reviewers: erik.pilkington, arphaman

Reviewed By: erik.pilkington

Subscribers: jkorous, dexonsmith, ilya-biryukov, Dmitry.Kozhevnikov

Differential Revision: https://reviews.llvm.org/D55095

llvm-svn: 348641

1 files changed, 6 insertions, 4 deletions

diff --git a/clang/lib/Lex/PPDirectives.cpp b/clang/lib/Lex/PPDirectives.cpp
index 541dfecd657..a61ba736250 100644
--- a/clang/lib/Lex/PPDirectives.cpp
+++ b/clang/lib/Lex/PPDirectives.cpp
@@ -1707,6 +1707,7 @@ void Preprocessor::HandleIncludeDirective(SourceLocation HashLoc,
   // Check that we don't have infinite #include recursion.
   if (IncludeMacroStack.size() == MaxAllowedIncludeStackDepth-1) {
     Diag(FilenameTok, diag::err_pp_include_too_deep);
+    HasReachedMaxIncludeDepth = true;
     return;
   }
 
@@ -1855,10 +1856,11 @@ void Preprocessor::HandleIncludeDirective(SourceLocation HashLoc,
   if (PPOpts->SingleFileParseMode)
     ShouldEnter = false;
 
-  // Any diagnostics after the fatal error will not be visible. As the
-  // compilation failed already and errors in subsequently included files won't
-  // be visible, avoid preprocessing those files.
-  if (ShouldEnter && Diags->hasFatalErrorOccurred())
+  // If we've reached the max allowed include depth, it is usually due to an
+  // include cycle. Don't enter already processed files again as it can lead to
+  // reaching the max allowed include depth again.
+  if (ShouldEnter && HasReachedMaxIncludeDepth && File &&
+      HeaderInfo.getFileInfo(File).NumIncludes)
     ShouldEnter = false;
 
   // Determine whether we should try to import the module for this #include, if