[BOLT] Fix state of MCSymbols in lowering pass

We have mostly harmless data races when running
BinaryContext::calculateEmittedSize() in parallel, while performing
split function pass.  However, it is possible to end up in a state
where some MCSymbols are still registered and our clean up
failed. This happens rarely but it does happen, and when it happens,
it is a difficult to diagnose heisenbug. To avoid this, add a new
clean pass to perform a last check on MCSymbols, before they
undergo our final emission pass, to verify that they are in a sane
state. If we fail to do this, we might resolve some symbols to zero
and crash the output binary.

Reviewed By: #bolt, Amir

Differential Revision: https://reviews.llvm.org/D137984

1 files changed, 4 insertions, 0 deletions

diff --git a/bolt/lib/Rewrite/BinaryPassManager.cpp b/bolt/lib/Rewrite/BinaryPassManager.cpp
index 53a45ab..dd00d62 100644
--- a/bolt/lib/Rewrite/BinaryPassManager.cpp
+++ b/bolt/lib/Rewrite/BinaryPassManager.cpp
@@ -488,6 +488,10 @@ void BinaryFunctionPassManager::runAllPasses(BinaryContext &BC) {
 
   Manager.registerPass(std::make_unique<LowerAnnotations>(NeverPrint));
 
+  // Check for dirty state of MCSymbols caused by running calculateEmittedSize
+  // in parallel and restore them
+  Manager.registerPass(std::make_unique<CleanMCState>(NeverPrint));
+
   Manager.runPasses();
 }