Restrict the definition of loop preheader to avoid EH blocks

Differential Revision: https://reviews.llvm.org/D34487

llvm-svn: 306070

llvm/lib/IR/BasicBlock.cpp

@@ -355,6 +355,19 @@ bool BasicBlock::canSplitPredecessors() const {
   return true;
 }
 
+bool BasicBlock::isLegalToHoistInto() const {
+  auto *Term = getTerminator();
+  // No terminator means the block is under construction.
+  if (!Term)
+    return true;
+
+  // If the block has no successors, there can be no instructions to hoist.
+  assert(Term->getNumSuccessors() > 0);
+
+  // Instructions should not be hoisted across exception handling boundaries.
+  return !Term->isExceptional();
+}
+
 /// This splits a basic block into two at the specified
 /// instruction.  Note that all instructions BEFORE the specified iterator stay
 /// as part of the original basic block, an unconditional branch is added to