2 files changed, 15 insertions, 8 deletions
diff --git a/llvm/include/llvm/Analysis/MustExecute.h b/llvm/include/llvm/Analysis/MustExecute.h
index 82387476a6d..e643e4ec563 100644
--- a/llvm/include/llvm/Analysis/MustExecute.h
+++ b/llvm/include/llvm/Analysis/MustExecute.h
@@ -65,13 +65,16 @@ public:
   /// abnormally.
   bool headerMayThrow() const;
 
+  /// Returns true iff the block \p BB potentially may throw exception. It can
+  /// be false-positive in cases when we want to avoid complex analysis.
+  bool blockMayThrow(const BasicBlock *BB) const;
+
   /// Returns true iff any block of the loop for which this info is contains an
   /// instruction that may throw or otherwise exit abnormally.
   bool anyBlockMayThrow() const;
 
   /// Return true if we must reach the block \p BB under assumption that the
-  /// loop \p CurLoop is entered and no instruction throws or otherwise exits
-  /// abnormally.
+  /// loop \p CurLoop is entered.
   bool allLoopPathsLeadToBlock(const Loop *CurLoop, const BasicBlock *BB,
                                const DominatorTree *DT) const;
 
diff --git a/llvm/lib/Analysis/MustExecute.cpp b/llvm/lib/Analysis/MustExecute.cpp
index 7c1ce86d15b..7f0912de26b 100644
--- a/llvm/lib/Analysis/MustExecute.cpp
+++ b/llvm/lib/Analysis/MustExecute.cpp
@@ -26,6 +26,11 @@ bool LoopSafetyInfo::headerMayThrow() const {
   return HeaderMayThrow;
 }
 
+bool LoopSafetyInfo::blockMayThrow(const BasicBlock *BB) const {
+  (void)BB;
+  return anyBlockMayThrow();
+}
+
 bool LoopSafetyInfo::anyBlockMayThrow() const {
   return MayThrow;
 }
@@ -148,7 +153,10 @@ bool LoopSafetyInfo::allLoopPathsLeadToBlock(const Loop *CurLoop,
   // 3) Exit blocks which are not taken on 1st iteration.
   // Memoize blocks we've already checked.
   SmallPtrSet<const BasicBlock *, 4> CheckedSuccessors;
-  for (auto *Pred : Predecessors)
+  for (auto *Pred : Predecessors) {
+    // Predecessor block may throw, so it has a side exit.
+    if (blockMayThrow(Pred))
+      return false;
     for (auto *Succ : successors(Pred))
       if (CheckedSuccessors.insert(Succ).second &&
           Succ != BB && !Predecessors.count(Succ))
@@ -169,6 +177,7 @@ bool LoopSafetyInfo::allLoopPathsLeadToBlock(const Loop *CurLoop,
         if (CurLoop->contains(Succ) ||
             !CanProveNotTakenFirstIteration(Succ, DT, CurLoop))
           return false;
+  }
 
   // All predecessors can only lead us to BB.
   return true;
@@ -194,11 +203,6 @@ bool LoopSafetyInfo::isGuaranteedToExecute(const Instruction &Inst,
     return !headerMayThrow() ||
            Inst.getParent()->getFirstNonPHIOrDbg() == &Inst;
 
-  // Somewhere in this loop there is an instruction which may throw and make us
-  // exit the loop.
-  if (anyBlockMayThrow())
-    return false;
-
   // If there is a path from header to exit or latch that doesn't lead to our
   // instruction's block, return false.
   if (!allLoopPathsLeadToBlock(CurLoop, Inst.getParent(), DT))