1 files changed, 45 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/Scalar/LICM.cpp b/llvm/lib/Transforms/Scalar/LICM.cpp
index c239edaf666..48fc9553fdd 100644
--- a/llvm/lib/Transforms/Scalar/LICM.cpp
+++ b/llvm/lib/Transforms/Scalar/LICM.cpp
@@ -789,6 +789,41 @@ public:
 };
 } // namespace
 
+
+/// Return true if we know how to rewrite all uses of the given alloca after
+/// hoisting it out of the loop.  The main concerns are a) potential captures
+/// and b) invariant.start markers which don't capture, but are no longer
+/// valid w/o a corresponding invariant.end.
+static bool canRewriteUsesOfAlloca(AllocaInst &AI) {
+  // TODO: This looks a lot like capture tracking, but we need to remove any
+  // invariant starts if we extend the lifetime of the alloca by hoisting it.
+  // We should probably refactor capture tracking into a form which allows us
+  // to reuse the relevant bits and remove the duplicated logic here.
+
+  SmallVector<Use *, 16> Worklist;
+  for (Use &U : AI.uses())
+    Worklist.push_back(&U);
+  
+  unsigned NumUsesExplored = 0;
+  while (!Worklist.empty()) {
+    Use *U = Worklist.pop_back_val();
+    Instruction *I = cast<Instruction>(U->getUser());
+    NumUsesExplored++;
+    if (NumUsesExplored > DefaultMaxUsesToExplore)
+      return false;
+    // Non capturing, terminating uses
+    if (isa<LoadInst>(I) ||
+        (isa<StoreInst>(I) && U->getOperandNo() == 1))
+      continue;
+    // Non capturing, non-terminating
+    if (!isa<BitCastInst>(I) && !isa<GetElementPtrInst>(I))
+      return false;
+    for (Use &U : I->uses())
+      Worklist.push_back(&U);
+  }
+  return true;
+}
+
 /// Walk the specified region of the CFG (defined by all blocks dominated by
 /// the specified block, and that are in the current loop) in depth first
 /// order w.r.t the DominatorTree.  This allows us to visit definitions before
@@ -909,6 +944,16 @@ bool llvm::hoistRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
         continue;
       }
 
+      if (isa<AllocaInst>(&I) &&
+          SafetyInfo->isGuaranteedToExecute(I, DT, CurLoop) &&
+          canRewriteUsesOfAlloca(cast<AllocaInst>(I))) {
+        hoist(I, DT, CurLoop, CFH.getOrCreateHoistedBlock(BB), SafetyInfo,
+              MSSAU, SE, ORE);
+        HoistedInstructions.push_back(&I);
+        Changed = true;
+        continue;
+      }
+
       if (PHINode *PN = dyn_cast<PHINode>(&I)) {
         if (CFH.canHoistPHI(PN)) {
           // Redirect incoming blocks first to ensure that we create hoisted