1 files changed, 65 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/Utils/LoopUtils.cpp b/llvm/lib/Transforms/Utils/LoopUtils.cpp
index e545bc0eb36..0ed33945ef4 100644
--- a/llvm/lib/Transforms/Utils/LoopUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUtils.cpp
@@ -12,6 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Transforms/Utils/LoopUtils.h"
+#include "llvm/ADT/ScopeExit.h"
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Analysis/BasicAliasAnalysis.h"
 #include "llvm/Analysis/GlobalsModRef.h"
@@ -29,6 +30,7 @@
 #include "llvm/IR/ValueHandle.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
 
 using namespace llvm;
 using namespace llvm::PatternMatch;
@@ -922,6 +924,69 @@ bool InductionDescriptor::isInductionPHI(PHINode *Phi, const Loop *TheLoop,
   return true;
 }
 
+bool llvm::formDedicatedExitBlocks(Loop *L, DominatorTree *DT, LoopInfo *LI,
+                                   bool PreserveLCSSA) {
+  bool Changed = false;
+
+  // We re-use a vector for the in-loop predecesosrs.
+  SmallVector<BasicBlock *, 4> InLoopPredecessors;
+
+  auto RewriteExit = [&](BasicBlock *BB) {
+    assert(InLoopPredecessors.empty() &&
+           "Must start with an empty predecessors list!");
+    auto Cleanup = make_scope_exit([&] { InLoopPredecessors.clear(); });
+
+    // See if there are any non-loop predecessors of this exit block and
+    // keep track of the in-loop predecessors.
+    bool IsDedicatedExit = true;
+    for (auto *PredBB : predecessors(BB))
+      if (L->contains(PredBB)) {
+        if (isa<IndirectBrInst>(PredBB->getTerminator()))
+          // We cannot rewrite exiting edges from an indirectbr.
+          return false;
+
+        InLoopPredecessors.push_back(PredBB);
+      } else {
+        IsDedicatedExit = false;
+      }
+
+    assert(!InLoopPredecessors.empty() && "Must have *some* loop predecessor!");
+
+    // Nothing to do if this is already a dedicated exit.
+    if (IsDedicatedExit)
+      return false;
+
+    auto *NewExitBB = SplitBlockPredecessors(
+        BB, InLoopPredecessors, ".loopexit", DT, LI, PreserveLCSSA);
+
+    if (!NewExitBB)
+      DEBUG(dbgs() << "WARNING: Can't create a dedicated exit block for loop: "
+                   << *L << "\n");
+    else
+      DEBUG(dbgs() << "LoopSimplify: Creating dedicated exit block "
+                   << NewExitBB->getName() << "\n");
+    return true;
+  };
+
+  // Walk the exit blocks directly rather than building up a data structure for
+  // them, but only visit each one once.
+  SmallPtrSet<BasicBlock *, 4> Visited;
+  for (auto *BB : L->blocks())
+    for (auto *SuccBB : successors(BB)) {
+      // We're looking for exit blocks so skip in-loop successors.
+      if (L->contains(SuccBB))
+        continue;
+
+      // Visit each exit block exactly once.
+      if (!Visited.insert(SuccBB).second)
+        continue;
+
+      Changed |= RewriteExit(SuccBB);
+    }
+
+  return Changed;
+}
+
 /// \brief Returns the instructions that use values defined in the loop.
 SmallVector<Instruction *, 8> llvm::findDefsUsedOutsideOfLoop(Loop *L) {
   SmallVector<Instruction *, 8> UsedOutside;