Fix 12513: Loop unrolling breaks with indirect branches.

Take this opportunity to generalize the indirectbr bailout logic for
loop transformations. CFG transformations will never get indirectbr
right, and there's no point trying.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154386 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 29 insertions, 29 deletions

diff --git a/lib/Analysis/LoopInfo.cpp b/lib/Analysis/LoopInfo.cpp
index 858cc642f4..f7a60a1737 100644
--- a/lib/Analysis/LoopInfo.cpp
+++ b/lib/Analysis/LoopInfo.cpp
@@ -205,6 +205,17 @@ bool Loop::isLoopSimplifyForm() const {
   return getLoopPreheader() && getLoopLatch() && hasDedicatedExits();
 }
 
+/// isSafeToClone - Return true if the loop body is safe to clone in practice.
+/// Routines that reform the loop CFG and split edges often fail on indirectbr.
+bool Loop::isSafeToClone() const {
+  // Return false if any loop blocks contain indirectbrs.
+  for (Loop::block_iterator I = block_begin(), E = block_end(); I != E; ++I) {
+    if (isa<IndirectBrInst>((*I)->getTerminator()))
+      return false;
+  }
+  return true;
+}
+
 /// hasDedicatedExits - Return true if no exit block for the loop
 /// has a predecessor that is outside the loop.
 bool Loop::hasDedicatedExits() const {
diff --git a/lib/Transforms/Scalar/LoopUnswitch.cpp b/lib/Transforms/Scalar/LoopUnswitch.cpp
index 1c93a703d6..ee232687ff 100644
--- a/lib/Transforms/Scalar/LoopUnswitch.cpp
+++ b/lib/Transforms/Scalar/LoopUnswitch.cpp
@@ -192,10 +192,6 @@ namespace {
       loopPreheader = currentLoop->getLoopPreheader();
     }
 
-    /// HasIndirectBrsInPreds - Returns true if there are predecessors, that are
-    /// terminated with indirect branch instruction.
-    bool HasIndirectBrsInPreds(const SmallVectorImpl<BasicBlock *> &ExitBlocks);
-
     /// Split all of the edges from inside the loop to their exit blocks.
     /// Update the appropriate Phi nodes as we do so.
     void SplitExitEdges(Loop *L, const SmallVector<BasicBlock *, 8> &ExitBlocks);
@@ -203,7 +199,7 @@ namespace {
     bool UnswitchIfProfitable(Value *LoopCond, Constant *Val);
     void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val,
                                   BasicBlock *ExitBlock);
-    bool UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L);
+    void UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L);
 
     void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
                                               Constant *Val, bool isEqual);
@@ -409,6 +405,14 @@ bool LoopUnswitch::processCurrentLoop() {
   if (!loopPreheader)
     return false;
 
+  // Loops with indirectbr cannot be cloned.
+  if (!currentLoop->isSafeToClone())
+    return false;
+
+  // Without dedicated exits, splitting the exit edge may fail.
+  if (!currentLoop->hasDedicatedExits())
+    return false;
+
   LLVMContext &Context = loopHeader->getContext();
 
   // Probably we reach the quota of branches for this loop. If so
@@ -638,7 +642,8 @@ bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val) {
   if (OptimizeForSize || F->hasFnAttr(Attribute::OptimizeForSize))
     return false;
 
-  return UnswitchNontrivialCondition(LoopCond, Val, currentLoop);
+  UnswitchNontrivialCondition(LoopCond, Val, currentLoop);
+  return true;
 }
 
 /// CloneLoop - Recursively clone the specified loop and all of its children,
@@ -733,24 +738,6 @@ void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond,
   ++NumTrivial;
 }
 
-/// HasIndirectBrsInPreds - Returns true if there are predecessors, that are
-/// terminated with indirect branch instruction.
-bool LoopUnswitch::HasIndirectBrsInPreds(
-     const SmallVectorImpl<BasicBlock *> &ExitBlocks){
-
-  for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
-    const BasicBlock *ExitBlock = ExitBlocks[i];
-    for (const_pred_iterator p = pred_begin(ExitBlock), e = pred_end(ExitBlock);
-         p != e; ++p) {
-      // Cannot split an edge from an IndirectBrInst
-      if (isa<IndirectBrInst>((*p)->getTerminator()))
-        return true;
-
-    }
-  }
-  return false;
-}
-
 /// SplitExitEdges - Split all of the edges from inside the loop to their exit
 /// blocks.  Update the appropriate Phi nodes as we do so.
 void LoopUnswitch::SplitExitEdges(Loop *L,
@@ -776,7 +763,7 @@ void LoopUnswitch::SplitExitEdges(Loop *L,
 /// UnswitchNontrivialCondition - We determined that the loop is profitable
 /// to unswitch when LIC equal Val.  Split it into loop versions and test the
 /// condition outside of either loop.  Return the loops created as Out1/Out2.
-bool LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
+void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
                                                Loop *L) {
   Function *F = loopHeader->getParent();
   DEBUG(dbgs() << "loop-unswitch: Unswitching loop %"
@@ -800,8 +787,6 @@ bool LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
 
   SmallVector<BasicBlock*, 8> ExitBlocks;
   L->getUniqueExitBlocks(ExitBlocks);
-  if (HasIndirectBrsInPreds(ExitBlocks))
-    return false;
 
   // Split all of the edges from inside the loop to their exit blocks.  Update
   // the appropriate Phi nodes as we do so.
@@ -916,8 +901,6 @@ bool LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
   if (!LoopProcessWorklist.empty() && LoopProcessWorklist.back() == NewLoop &&
       LICHandle && !isa<Constant>(LICHandle))
     RewriteLoopBodyWithConditionConstant(NewLoop, LICHandle, Val, true);
-
-  return true;
 }
 
 /// RemoveFromWorklist - Remove all instances of I from the worklist vector
diff --git a/lib/Transforms/Utils/LoopUnroll.cpp b/lib/Transforms/Utils/LoopUnroll.cpp
index 512b689501..e15497a77a 100644
--- a/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/lib/Transforms/Utils/LoopUnroll.cpp
@@ -149,6 +149,12 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
     return false;
   }
 
+  // Loops with indirectbr cannot be cloned.
+  if (!L->isSafeToClone()) {
+    DEBUG(dbgs() << "  Can't unroll; Loop body cannot be cloned.\n");
+    return false;
+  }
+
   BasicBlock *Header = L->getHeader();
   BranchInst *BI = dyn_cast<BranchInst>(LatchBlock->getTerminator());