[LoopPeel] Peel loops with exits followed by an unreachable or deopt block

Added support for peeling loops with exits that are followed either by an
unreachable-terminated block or block that has a terminatnig deoptimize call.
All blocks in the sequence must have an unique successor, maybe except
for the last one.

Reviewed By: mkazantsev

Differential Revision: https://reviews.llvm.org/D110922

1 files changed, 21 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
index 1a07697..6469c89 100644
--- a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -39,6 +39,7 @@
 #include "llvm/IR/Value.h"
 #include "llvm/IR/ValueHandle.h"
 #include "llvm/Support/Casting.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Transforms/Utils/Local.h"
@@ -52,6 +53,12 @@ using namespace llvm;
 
 #define DEBUG_TYPE "basicblock-utils"
 
+static cl::opt<unsigned> MaxDeoptOrUnreachableSuccessorCheckDepth(
+    "max-deopt-or-unreachable-succ-check-depth", cl::init(8), cl::Hidden,
+    cl::desc("Set the maximum path length when checking whether a basic block "
+             "is followed by a block that either has a terminating "
+             "deoptimizing call or is terminated with an unreachable"));
+
 void llvm::DetatchDeadBlocks(
     ArrayRef<BasicBlock *> BBs,
     SmallVectorImpl<DominatorTree::UpdateType> *Updates,
@@ -485,6 +492,20 @@ void llvm::ReplaceInstWithInst(BasicBlock::InstListType &BIL,
   BI = New;
 }
 
+bool llvm::IsBlockFollowedByDeoptOrUnreachable(const BasicBlock *BB) {
+  // Remember visited blocks to avoid infinite loop
+  SmallPtrSet<const BasicBlock *, 8> VisitedBlocks;
+  unsigned Depth = 0;
+  while (BB && Depth++ < MaxDeoptOrUnreachableSuccessorCheckDepth &&
+         VisitedBlocks.insert(BB).second) {
+    if (BB->getTerminatingDeoptimizeCall() ||
+        isa<UnreachableInst>(BB->getTerminator()))
+      return true;
+    BB = BB->getUniqueSuccessor();
+  }
+  return false;
+}
+
 void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) {
   BasicBlock::iterator BI(From);
   ReplaceInstWithInst(From->getParent()->getInstList(), BI, To);