[LV] Relax assumption that LCSSA implies single entry

[reames]

Summary

This relates to the ongoing effort to support vectorization of multiple exit loops (see D93317).

The previous code assumed that LCSSA phis were always single entry before the vectorizer ran. This was correct, but only because the vectorizer allowed only a single exiting edge. There's nothing in the definition of LCSSA which requires single entry phis.

A common case where this comes up is with a loop with multiple exiting blocks which all reach a common exit block. (e.g. see the test updates)

[reames]

ping now that previous patch in series has landed

[reames]

ping

[fhahn]

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

634–635

This also needs updating now, right? The exit may have phis with multiple incoming values and it needs to fix PHIs without incoming values from the 'middle' block.

4160

This is because we run the last iteration in the scalar loop, right? I think it would be good to extend the comment. Also, the same comment also applies to the similar code in fixReduction and fixLCSSAPHIs as well?

And could you add a test case where we have LCSSA phis where some incoming values are different to the recurrence, as in

define i16 @test(i16* %p, i32 %n) {
entry:
  br label %for.cond

for.cond:
  %i = phi i32 [ 0, %entry ], [ %inc, %for.body ]
  %rec = phi i16 [0, %entry], [ %rec.next, %for.body ]
  %iprom = sext i32 %i to i64
  %b = getelementptr inbounds i16, i16* %p, i64 %iprom
  %rec.next = load i16, i16* %b
  %cmp = icmp slt i32 %i, %n
  br i1 %cmp, label %for.body, label %if.end

for.body:
  store i16 %rec , i16* %b, align 4
  %inc = add nsw i32 %i, 1
  %cmp2 = icmp slt i32 %i, 2096
  br i1 %cmp2, label %for.cond, label %if.end

if.end:
  %rec.lcssa = phi i16 [ %rec, %for.cond ], [ 10, %for.body ]
  ret i16 %rec.lcssa
}

4162

nit: personally I find using any_of slightly more explicit, like

if (any_of(LCSSAPhi.incoming_values(), [Phi](Value *V) { return V == Phi; }))
  LCSSAPhi.addIncoming(ExtractForPhiUsedOutsideLoop, LoopMiddleBlock);

but that's down to personal preference

4369

Should that be reduction and recurrence code above?

llvm/test/Transforms/LoopVectorize/loop-form.ll

349

can you also add a test with multiple unique exits & first-order recurrences/reductions?

like

define i16 @multiple_unique_exit_fof(i16* %p, i32 %n) {
entry:
  br label %for.cond

for.cond:
  %i = phi i32 [ 0, %entry ], [ %inc, %for.body ]
  %rec = phi i16 [0, %entry], [ %rec.next, %for.body ]
  %iprom = sext i32 %i to i64
  %b = getelementptr inbounds i16, i16* %p, i64 %iprom
  %rec.next = load i16, i16* %b
  %cmp = icmp slt i32 %i, %n
  br i1 %cmp, label %for.body, label %if.end

for.body:
  store i16 %rec , i16* %b, align 4
  %inc = add nsw i32 %i, 1
  %cmp2 = icmp slt i32 %i, 2096
  br i1 %cmp2, label %for.cond, label %if.end

if.end:
  ret i16 %rec
}

Not sure if loop-form.ll would be the right place, perhaps adding them to llvm/test/Transforms/LoopVectorize/first-order-recurrence.ll and llvm/test/Transforms/LoopVectorize/reduction.ll respectively would be better.

[reames]

Address stylistic updates. Test changes to be done separately in near future.

[reames]

Add requested test.

Will rebase over test additions and reformats shortly.

[reames]

rebase over landed tests

Ready for re-review.

[fhahn]

LGTM, thanks!

llvm/test/Transforms/LoopVectorize/loop-form.ll

937

nit: would be good to have a comment that this tests multi exit & reductions, perhaps also add it to the name?

llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp

bool LoopVectorizationLegality::canVectorizeLoopCFG(Loop *Lp,
   }
 
   // We currently must have a single "exit block" after the loop. Note that
   // multiple "exiting blocks" inside the loop are allowed, provided they all
   // reach the single exit block.
   // TODO: This restriction can be relaxed in the near future, it's here solely
   // to allow separation of changes for review. We need to generalize the phi
   // update logic in a number of places.
-  BasicBlock *ExitBB = Lp->getUniqueExitBlock();
-  if (!ExitBB) {
+  if (!Lp->getUniqueExitBlock()) {
     reportVectorizationFailure("The loop must have a unique exit block",
         "loop control flow is not understood by vectorizer",
         "CFGNotUnderstood", ORE, TheLoop);
     if (DoExtraAnalysis)
       Result = false;
     else
       return false;
-  } else {
-    // The existing code assumes that LCSSA implies that phis are single entry
-    // (which was true when we had at most a single exiting edge from the latch).
-    // In general, there's nothing which prevents an LCSSA phi in exit block from
-    // having two or more values if there are multiple exiting edges leading to
-    // the exit block.  (TODO: implement general case)
-    if (!llvm::empty(ExitBB->phis()) && !ExitBB->getSinglePredecessor()) {
-      reportVectorizationFailure("The loop must have no live-out values if "
-                                 "it has more than one exiting block",
-          "loop control flow is not understood by vectorizer",
-          "CFGNotUnderstood", ORE, TheLoop);
-      if (DoExtraAnalysis)
-        Result = false;
-      else
-        return false;
-    }
-  }
-
   return Result;
 }
 
 bool LoopVectorizationLegality::canVectorizeLoopNestCFG(
     Loop *Lp, bool UseVPlanNativePath) {
   // Store the result and return it at the end instead of exiting early, in case
   // allowExtraAnalysis is used to report multiple reasons for not vectorizing.
   bool Result = true;

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

protected:
   void fixFirstOrderRecurrence(PHINode *Phi);
 
   /// Fix a reduction cross-iteration phi. This is the second phase of
   /// vectorizing this phi node.
   void fixReduction(PHINode *Phi);
 
   /// Clear NSW/NUW flags from reduction instructions if necessary.
   void clearReductionWrapFlags(RecurrenceDescriptor &RdxDesc);
 
-  /// The Loop exit block may have single value PHI nodes with some
-  /// incoming value. While vectorizing we only handled real values
-  /// that were defined inside the loop and we should have one value for
-  /// each predecessor of its parent basic block. See PR14725.
+  /// Fixup the LCSSA phi nodes in the unique exit block.  This simply
+  /// means we need to add the appropriate incoming value from the middle
+  /// block as exiting edges from the scalar epilogue loop (if present) are
+  /// already in place, and we exit the vector loop exclusively to the middle
+  /// block.
   void fixLCSSAPHIs();
 
   /// Iteratively sink the scalarized operands of a predicated instruction into
   /// the block that was created for it.
   void sinkScalarOperands(Instruction *PredInst);
 
   /// Shrinks vector element sizes to the smallest bitwidth they can be legally
   /// represented as.
void InnerLoopVectorizer::fixFirstOrderRecurrence(PHINode *Phi) {
   Phi->setIncomingValueForBlock(LoopScalarPreHeader, Start);
   Phi->setName("scalar.recur");
 
   // Finally, fix users of the recurrence outside the loop. The users will need
   // either the last value of the scalar recurrence or the last value of the
   // vector recurrence we extracted in the middle block. Since the loop is in
   // LCSSA form, we just need to find all the phi nodes for the original scalar
   // recurrence in the exit block, and then add an edge for the middle block.
-  for (PHINode &LCSSAPhi : LoopExitBlock->phis()) {
-    if (LCSSAPhi.getIncomingValue(0) == Phi) {
+  // Note that LCSSA does not imply single entry when the original scalar loop
+  // had multiple exiting edges (as we always run the last iteration in the
+  // scalar epilogue); in that case, the exiting path through middle will be
+  // dynamically dead and the value picked for the phi doesn't matter.
+  for (PHINode &LCSSAPhi : LoopExitBlock->phis())
+    if (any_of(LCSSAPhi.incoming_values(),
+               [Phi](Value *V) { return V == Phi; }))
       LCSSAPhi.addIncoming(ExtractForPhiUsedOutsideLoop, LoopMiddleBlock);
-    }
-  }
-}
 
 void InnerLoopVectorizer::fixReduction(PHINode *Phi) {
   // Get it's reduction variable descriptor.
   assert(Legal->isReductionVariable(Phi) &&
          "Unable to find the reduction variable");
   RecurrenceDescriptor RdxDesc = Legal->getReductionVars()[Phi];
 
   RecurKind RK = RdxDesc.getRecurrenceKind();
   TrackingVH<Value> ReductionStartValue = RdxDesc.getRecurrenceStartValue();
   Instruction *LoopExitInst = RdxDesc.getLoopExitInstr();
   setDebugLocFromInst(Builder, ReductionStartValue);
void InnerLoopVectorizer::fixReduction(PHINode *Phi) {
   PHINode *BCBlockPhi = PHINode::Create(Phi->getType(), 2, "bc.merge.rdx",
                                         LoopScalarPreHeader->getTerminator());
   for (unsigned I = 0, E = LoopBypassBlocks.size(); I != E; ++I)
     BCBlockPhi->addIncoming(ReductionStartValue, LoopBypassBlocks[I]);
   BCBlockPhi->addIncoming(ReducedPartRdx, LoopMiddleBlock);
 
   // Now, we need to fix the users of the reduction variable
   // inside and outside of the scalar remainder loop.
-  // We know that the loop is in LCSSA form. We need to update the
-  // PHI nodes in the exit blocks.
-  for (PHINode &LCSSAPhi : LoopExitBlock->phis()) {
-    // All PHINodes need to have a single entry edge, or two if
-    // we already fixed them.
-    assert(LCSSAPhi.getNumIncomingValues() < 3 && "Invalid LCSSA PHI");
-
-    // We found a reduction value exit-PHI. Update it with the
-    // incoming bypass edge.
-    if (LCSSAPhi.getIncomingValue(0) == LoopExitInst)
+
+  // We know that the loop is in LCSSA form. We need to update the PHI nodes
+  // in the exit blocks.  See comment on analogous loop in
+  // fixFirstOrderRecurrence for a more complete explaination of the logic.
+  for (PHINode &LCSSAPhi : LoopExitBlock->phis())
+    if (any_of(LCSSAPhi.incoming_values(),
+               [LoopExitInst](Value *V) { return V == LoopExitInst; }))
       LCSSAPhi.addIncoming(ReducedPartRdx, LoopMiddleBlock);
-  } // end of the LCSSA phi scan.
 
-    // Fix the scalar loop reduction variable with the incoming reduction sum
-    // from the vector body and from the backedge value.
   int IncomingEdgeBlockIdx =
     Phi->getBasicBlockIndex(OrigLoop->getLoopLatch());
   assert(IncomingEdgeBlockIdx >= 0 && "Invalid block index");
   // Pick the other block.
   int SelfEdgeBlockIdx = (IncomingEdgeBlockIdx ? 0 : 1);
   Phi->setIncomingValue(SelfEdgeBlockIdx, BCBlockPhi);
   Phi->setIncomingValue(IncomingEdgeBlockIdx, LoopExitInst);
 }
for (User *U : Cur->users()) {
           Visited.insert(UI).second)
         Worklist.push_back(UI);
     }
   }
 }
 
 void InnerLoopVectorizer::fixLCSSAPHIs() {
   for (PHINode &LCSSAPhi : LoopExitBlock->phis()) {
-    if (LCSSAPhi.getNumIncomingValues() == 1) {
-      auto *IncomingValue = LCSSAPhi.getIncomingValue(0);
-      // Non-instruction incoming values will have only one value.
-      unsigned LastLane = 0;
-      if (isa<Instruction>(IncomingValue))
-        LastLane = Cost->isUniformAfterVectorization(
-                       cast<Instruction>(IncomingValue), VF)
-                       ? 0
-                       : VF.getKnownMinValue() - 1;
-      assert((!VF.isScalable() || LastLane == 0) &&
-             "scalable vectors dont support non-uniform scalars yet");
-      // Can be a loop invariant incoming value or the last scalar value to be
-      // extracted from the vectorized loop.
-      Builder.SetInsertPoint(LoopMiddleBlock->getTerminator());
-      Value *lastIncomingValue =
-          getOrCreateScalarValue(IncomingValue, { UF - 1, LastLane });
-      LCSSAPhi.addIncoming(lastIncomingValue, LoopMiddleBlock);
-    }
-  }
-}
+    if (LCSSAPhi.getBasicBlockIndex(LoopMiddleBlock) != -1)
+      // Some phis were already hand updated by the reduction and recurrence
+      // code above, leave them alone.
+      continue;
+
 
 void InnerLoopVectorizer::sinkScalarOperands(Instruction *PredInst) {
   // The basic block and loop containing the predicated instruction.
   auto *PredBB = PredInst->getParent();
   auto *VectorLoop = LI->getLoopFor(PredBB);
 
   // Initialize a worklist with the operands of the predicated instruction.
   SetVector<Value *> Worklist(PredInst->op_begin(), PredInst->op_end());

llvm/test/Transforms/LoopVectorize/loop-form.ll

 if.end:
   ret void
 }
 
 ; multiple exit - with an lcssa phi
 define i32 @multiple_unique_exit2(i16* %p, i32 %n) {
 ; CHECK-LABEL: @multiple_unique_exit2(
 ; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = icmp sgt i32 [[N:%.*]], 0
+; CHECK-NEXT:    [[SMAX:%.*]] = select i1 [[TMP0]], i32 [[N]], i32 0
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ult i32 [[SMAX]], 2096
+; CHECK-NEXT:    [[UMIN:%.*]] = select i1 [[TMP1]], i32 [[SMAX]], i32 2096
+; CHECK-NEXT:    [[TMP2:%.*]] = add nuw nsw i32 [[UMIN]], 1
+; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ule i32 [[TMP2]], 2
+; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label [[SCALAR_PH:%.*]], label [[VECTOR_PH:%.*]]
+; CHECK:       vector.ph:
+; CHECK-NEXT:    [[N_MOD_VF:%.*]] = urem i32 [[TMP2]], 2
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp eq i32 [[N_MOD_VF]], 0
+; CHECK-NEXT:    [[TMP4:%.*]] = select i1 [[TMP3]], i32 2, i32 [[N_MOD_VF]]
+; CHECK-NEXT:    [[N_VEC:%.*]] = sub i32 [[TMP2]], [[TMP4]]
+; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
+; CHECK:       vector.body:
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_IND:%.*]] = phi <2 x i32> [ <i32 0, i32 1>, [[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[TMP5:%.*]] = add i32 [[INDEX]], 0
+; CHECK-NEXT:    [[TMP6:%.*]] = add i32 [[INDEX]], 1
+; CHECK-NEXT:    [[TMP7:%.*]] = sext i32 [[TMP5]] to i64
+; CHECK-NEXT:    [[TMP8:%.*]] = getelementptr inbounds i16, i16* [[P:%.*]], i64 [[TMP7]]
+; CHECK-NEXT:    [[TMP9:%.*]] = getelementptr inbounds i16, i16* [[TMP8]], i32 0
+; CHECK-NEXT:    [[TMP10:%.*]] = bitcast i16* [[TMP9]] to <2 x i16>*
+; CHECK-NEXT:    store <2 x i16> zeroinitializer, <2 x i16>* [[TMP10]], align 4
+; CHECK-NEXT:    [[INDEX_NEXT]] = add i32 [[INDEX]], 2
+; CHECK-NEXT:    [[VEC_IND_NEXT]] = add <2 x i32> [[VEC_IND]], <i32 2, i32 2>
+; CHECK-NEXT:    [[TMP11:%.*]] = icmp eq i32 [[INDEX_NEXT]], [[N_VEC]]
+; CHECK-NEXT:    br i1 [[TMP11]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], [[LOOP8:!llvm.loop !.*]]
+; CHECK:       middle.block:
+; CHECK-NEXT:    [[CMP_N:%.*]] = icmp eq i32 [[TMP2]], [[N_VEC]]
+; CHECK-NEXT:    [[IND_ESCAPE:%.*]] = sub i32 [[N_VEC]], 1
+; CHECK-NEXT:    [[IND_ESCAPE1:%.*]] = sub i32 [[N_VEC]], 1
+; CHECK-NEXT:    br i1 [[CMP_N]], label [[IF_END:%.*]], label [[SCALAR_PH]]
+; CHECK:       scalar.ph:
+; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i32 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    br label [[FOR_COND:%.*]]
 ; CHECK:       for.cond:
-; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[INC:%.*]], [[FOR_BODY:%.*]] ]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[I]], [[N:%.*]]
-; CHECK-NEXT:    br i1 [[CMP]], label [[FOR_BODY]], label [[IF_END:%.*]]
+; CHECK-NEXT:    [[I:%.*]] = phi i32 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[INC:%.*]], [[FOR_BODY:%.*]] ]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[I]], [[N]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[FOR_BODY]], label [[IF_END]]
 ; CHECK:       for.body:
 ; CHECK-NEXT:    [[IPROM:%.*]] = sext i32 [[I]] to i64
-; CHECK-NEXT:    [[B:%.*]] = getelementptr inbounds i16, i16* [[P:%.*]], i64 [[IPROM]]
+; CHECK-NEXT:    [[B:%.*]] = getelementptr inbounds i16, i16* [[P]], i64 [[IPROM]]
 ; CHECK-NEXT:    store i16 0, i16* [[B]], align 4
 ; CHECK-NEXT:    [[INC]] = add nsw i32 [[I]], 1
 ; CHECK-NEXT:    [[CMP2:%.*]] = icmp slt i32 [[I]], 2096
-; CHECK-NEXT:    br i1 [[CMP2]], label [[FOR_COND]], label [[IF_END]]
+; CHECK-NEXT:    br i1 [[CMP2]], label [[FOR_COND]], label [[IF_END]], [[LOOP9:!llvm.loop !.*]]
 ; CHECK:       if.end:
-; CHECK-NEXT:    [[I_LCSSA:%.*]] = phi i32 [ [[I]], [[FOR_BODY]] ], [ [[I]], [[FOR_COND]] ]
+; CHECK-NEXT:    [[I_LCSSA:%.*]] = phi i32 [ [[I]], [[FOR_BODY]] ], [ [[I]], [[FOR_COND]] ], [ [[IND_ESCAPE1]], [[MIDDLE_BLOCK]] ]
 ; CHECK-NEXT:    ret i32 [[I_LCSSA]]
 ;
 ; TAILFOLD-LABEL: @multiple_unique_exit2(
 ; TAILFOLD-NEXT:  entry:
 ; TAILFOLD-NEXT:    br label [[FOR_COND:%.*]]
 ; TAILFOLD:       for.cond:
 ; TAILFOLD-NEXT:    [[I:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[INC:%.*]], [[FOR_BODY:%.*]] ]
 ; TAILFOLD-NEXT:    [[CMP:%.*]] = icmp slt i32 [[I]], [[N:%.*]]

 if.end:
   ret i32 %i
 }
 
 ; multiple exit w/a non lcssa phi
 define i32 @multiple_unique_exit3(i16* %p, i32 %n) {
 ; CHECK-LABEL: @multiple_unique_exit3(
 ; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = icmp sgt i32 [[N:%.*]], 0
+; CHECK-NEXT:    [[SMAX:%.*]] = select i1 [[TMP0]], i32 [[N]], i32 0
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ult i32 [[SMAX]], 2096
+; CHECK-NEXT:    [[UMIN:%.*]] = select i1 [[TMP1]], i32 [[SMAX]], i32 2096
+; CHECK-NEXT:    [[TMP2:%.*]] = add nuw nsw i32 [[UMIN]], 1
+; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ule i32 [[TMP2]], 2
+; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label [[SCALAR_PH:%.*]], label [[VECTOR_PH:%.*]]
+; CHECK:       vector.ph:
+; CHECK-NEXT:    [[N_MOD_VF:%.*]] = urem i32 [[TMP2]], 2
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp eq i32 [[N_MOD_VF]], 0
+; CHECK-NEXT:    [[TMP4:%.*]] = select i1 [[TMP3]], i32 2, i32 [[N_MOD_VF]]
+; CHECK-NEXT:    [[N_VEC:%.*]] = sub i32 [[TMP2]], [[TMP4]]
+; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
+; CHECK:       vector.body:
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_IND:%.*]] = phi <2 x i32> [ <i32 0, i32 1>, [[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[TMP5:%.*]] = add i32 [[INDEX]], 0
+; CHECK-NEXT:    [[TMP6:%.*]] = add i32 [[INDEX]], 1
+; CHECK-NEXT:    [[TMP7:%.*]] = sext i32 [[TMP5]] to i64
+; CHECK-NEXT:    [[TMP8:%.*]] = getelementptr inbounds i16, i16* [[P:%.*]], i64 [[TMP7]]
+; CHECK-NEXT:    [[TMP9:%.*]] = getelementptr inbounds i16, i16* [[TMP8]], i32 0
+; CHECK-NEXT:    [[TMP10:%.*]] = bitcast i16* [[TMP9]] to <2 x i16>*
+; CHECK-NEXT:    store <2 x i16> zeroinitializer, <2 x i16>* [[TMP10]], align 4
+; CHECK-NEXT:    [[INDEX_NEXT]] = add i32 [[INDEX]], 2
+; CHECK-NEXT:    [[VEC_IND_NEXT]] = add <2 x i32> [[VEC_IND]], <i32 2, i32 2>
+; CHECK-NEXT:    [[TMP11:%.*]] = icmp eq i32 [[INDEX_NEXT]], [[N_VEC]]
+; CHECK-NEXT:    br i1 [[TMP11]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], [[LOOP10:!llvm.loop !.*]]
+; CHECK:       middle.block:
+; CHECK-NEXT:    [[CMP_N:%.*]] = icmp eq i32 [[TMP2]], [[N_VEC]]
+; CHECK-NEXT:    br i1 [[CMP_N]], label [[IF_END:%.*]], label [[SCALAR_PH]]
+; CHECK:       scalar.ph:
+; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i32 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    br label [[FOR_COND:%.*]]
 ; CHECK:       for.cond:
-; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[INC:%.*]], [[FOR_BODY:%.*]] ]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[I]], [[N:%.*]]
-; CHECK-NEXT:    br i1 [[CMP]], label [[FOR_BODY]], label [[IF_END:%.*]]
+; CHECK-NEXT:    [[I:%.*]] = phi i32 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[INC:%.*]], [[FOR_BODY:%.*]] ]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[I]], [[N]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[FOR_BODY]], label [[IF_END]]
 ; CHECK:       for.body:
 ; CHECK-NEXT:    [[IPROM:%.*]] = sext i32 [[I]] to i64
-; CHECK-NEXT:    [[B:%.*]] = getelementptr inbounds i16, i16* [[P:%.*]], i64 [[IPROM]]
+; CHECK-NEXT:    [[B:%.*]] = getelementptr inbounds i16, i16* [[P]], i64 [[IPROM]]
 ; CHECK-NEXT:    store i16 0, i16* [[B]], align 4
 ; CHECK-NEXT:    [[INC]] = add nsw i32 [[I]], 1
 ; CHECK-NEXT:    [[CMP2:%.*]] = icmp slt i32 [[I]], 2096
-; CHECK-NEXT:    br i1 [[CMP2]], label [[FOR_COND]], label [[IF_END]]
+; CHECK-NEXT:    br i1 [[CMP2]], label [[FOR_COND]], label [[IF_END]], [[LOOP11:!llvm.loop !.*]]
 ; CHECK:       if.end:
-; CHECK-NEXT:    [[EXIT:%.*]] = phi i32 [ 0, [[FOR_COND]] ], [ 1, [[FOR_BODY]] ]
+; CHECK-NEXT:    [[EXIT:%.*]] = phi i32 [ 0, [[FOR_COND]] ], [ 1, [[FOR_BODY]] ], [ 0, [[MIDDLE_BLOCK]] ]
 ; CHECK-NEXT:    ret i32 [[EXIT]]
 ;
 ; TAILFOLD-LABEL: @multiple_unique_exit3(
 ; TAILFOLD-NEXT:  entry:
 ; TAILFOLD-NEXT:    br label [[FOR_COND:%.*]]
 ; TAILFOLD:       for.cond:
 ; TAILFOLD-NEXT:    [[I:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[INC:%.*]], [[FOR_BODY:%.*]] ]
 ; TAILFOLD-NEXT:    [[CMP:%.*]] = icmp slt i32 [[I]], [[N:%.*]]
then:
   br label %loop.latch
 
 loop.latch:
   %iv.next = add nuw nsw i64 %iv, 1
   br label %loop.header
 
 exit:
   ret void
 }