[llvm] 43d2e51 - Return "[LoopDeletion] Break backedge if we can prove that the loop is exited on 1st iteration"
Max Kazantsev via llvm-commits
llvm-commits at lists.llvm.org
Wed May 26 05:27:30 PDT 2021
Author: Max Kazantsev
Date: 2021-05-26T19:23:21+07:00
New Revision: 43d2e51c2e86788b9e2a582fdd3d8ffa7829328a
URL: https://github.com/llvm/llvm-project/commit/43d2e51c2e86788b9e2a582fdd3d8ffa7829328a
DIFF: https://github.com/llvm/llvm-project/commit/43d2e51c2e86788b9e2a582fdd3d8ffa7829328a.diff
LOG: Return "[LoopDeletion] Break backedge if we can prove that the loop is exited on 1st iteration"
The patch was reverted due to compile time impact of contextual SCEV
queries. It also appeared that it introduced a miscompile on irreducible CFG.
Changes made:
1. isKnownPredicateAt is replaced with more lightweight isKnownPredicate;
2. Irreducible CFG in live code is now detected and excluded from processing.
Differential Revision: https://reviews.llvm.org/D102615
Added:
Modified:
llvm/lib/Transforms/Scalar/LoopDeletion.cpp
llvm/test/Transforms/LoopDeletion/eval_first_iteration.ll
llvm/test/Transforms/LoopDeletion/zero-btc.ll
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/Scalar/LoopDeletion.cpp b/llvm/lib/Transforms/Scalar/LoopDeletion.cpp
index fd0e983b6199a..2a080bfed67fe 100644
--- a/llvm/lib/Transforms/Scalar/LoopDeletion.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopDeletion.cpp
@@ -17,6 +17,7 @@
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/GlobalsModRef.h"
+#include "llvm/Analysis/LoopIterator.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/MemorySSA.h"
#include "llvm/Analysis/OptimizationRemarkEmitter.h"
@@ -135,6 +136,155 @@ static bool isLoopNeverExecuted(Loop *L) {
return true;
}
+static const SCEV *
+getSCEVOnFirstIteration(Value *V, Loop *L, ScalarEvolution &SE,
+ DenseMap<Value *, const SCEV *> &FirstIterSCEV) {
+ // Fist, check in cache.
+ auto Existing = FirstIterSCEV.find(V);
+ if (Existing != FirstIterSCEV.end())
+ return Existing->second;
+ const SCEV *S = nullptr;
+ // TODO: Once ScalarEvolution supports getValueOnNthIteration for anything
+ // else but AddRecs, it's a good use case for it. So far, just consider some
+ // simple cases, like arithmetic operations.
+ Value *LHS, *RHS;
+ using namespace PatternMatch;
+ if (match(V, m_Add(m_Value(LHS), m_Value(RHS)))) {
+ const SCEV *LHSS = getSCEVOnFirstIteration(LHS, L, SE, FirstIterSCEV);
+ const SCEV *RHSS = getSCEVOnFirstIteration(RHS, L, SE, FirstIterSCEV);
+ S = SE.getAddExpr(LHSS, RHSS);
+ } else if (match(V, m_Sub(m_Value(LHS), m_Value(RHS)))) {
+ const SCEV *LHSS = getSCEVOnFirstIteration(LHS, L, SE, FirstIterSCEV);
+ const SCEV *RHSS = getSCEVOnFirstIteration(RHS, L, SE, FirstIterSCEV);
+ S = SE.getMinusSCEV(LHSS, RHSS);
+ } else if (match(V, m_Mul(m_Value(LHS), m_Value(RHS)))) {
+ const SCEV *LHSS = getSCEVOnFirstIteration(LHS, L, SE, FirstIterSCEV);
+ const SCEV *RHSS = getSCEVOnFirstIteration(RHS, L, SE, FirstIterSCEV);
+ S = SE.getMulExpr(LHSS, RHSS);
+ } else
+ S = SE.getSCEV(V);
+ assert(S && "Case not handled?");
+ FirstIterSCEV[V] = S;
+ return S;
+}
+
+// Try to prove that one of conditions that dominates the latch must exit on 1st
+// iteration.
+static bool canProveExitOnFirstIteration(Loop *L, DominatorTree &DT,
+ ScalarEvolution &SE, LoopInfo &LI) {
+ BasicBlock *Latch = L->getLoopLatch();
+
+ if (!Latch)
+ return false;
+
+ LoopBlocksRPO RPOT(L);
+ RPOT.perform(&LI);
+
+ BasicBlock *Header = L->getHeader();
+ // Blocks that are reachable on the 1st iteration.
+ SmallPtrSet<BasicBlock *, 4> LiveBlocks;
+ // Edges that are reachable on the 1st iteration.
+ DenseSet<BasicBlockEdge> LiveEdges;
+ LiveBlocks.insert(L->getHeader());
+
+ auto MarkLiveEdge = [&](BasicBlock *From, BasicBlock *To) {
+ assert(LiveBlocks.count(From) && "Must be live!");
+ LiveBlocks.insert(To);
+ LiveEdges.insert({ From, To });
+ };
+
+ auto MarkAllSuccessorsLive = [&](BasicBlock *BB) {
+ for (auto *Succ : successors(BB))
+ MarkLiveEdge(BB, Succ);
+ };
+
+ // Check if there is only one predecessor on 1st iteration. Note that because
+ // we iterate in RPOT, we have already visited all its (non-latch)
+ // predecessors.
+ auto GetSolePredecessorOnFirstIteration = [&](BasicBlock * BB)->BasicBlock * {
+ if (BB == Header)
+ return L->getLoopPredecessor();
+ BasicBlock *OnlyPred = nullptr;
+ for (auto *Pred : predecessors(BB))
+ if (OnlyPred != Pred && LiveEdges.count({ Pred, BB })) {
+ // 2 live preds.
+ if (OnlyPred)
+ return nullptr;
+ OnlyPred = Pred;
+ }
+
+ assert(OnlyPred && "No live predecessors?");
+ return OnlyPred;
+ };
+ DenseMap<Value *, const SCEV *> FirstIterSCEV;
+
+ // Use the following algorithm to prove we never take the latch on the 1st
+ // iteration:
+ // 1. Traverse in topological order, so that whenever we visit a block, all
+ // its predecessors are already visited.
+ // 2. If we can prove that the block may have only 1 predecessor on the 1st
+ // iteration, map all its phis onto input from this predecessor.
+ // 3a. If we can prove which successor of out block is taken on the 1st
+ // iteration, mark this successor live.
+ // 3b. If we cannot prove it, conservatively assume that all successors are
+ // live.
+ for (auto *BB : RPOT) {
+ // This block is not reachable on the 1st iterations.
+ if (!LiveBlocks.count(BB))
+ continue;
+
+ // Skip inner loops.
+ if (LI.getLoopFor(BB) != L) {
+ MarkAllSuccessorsLive(BB);
+ continue;
+ }
+
+ // If this block has only one live pred, map its phis onto their SCEVs.
+ if (auto *OnlyPred = GetSolePredecessorOnFirstIteration(BB))
+ for (auto &PN : BB->phis()) {
+ if (!SE.isSCEVable(PN.getType()))
+ continue;
+ auto *Incoming = PN.getIncomingValueForBlock(OnlyPred);
+ if (DT.dominates(Incoming, BB->getTerminator())) {
+ const SCEV *IncSCEV =
+ getSCEVOnFirstIteration(Incoming, L, SE, FirstIterSCEV);
+ FirstIterSCEV[&PN] = IncSCEV;
+ }
+ }
+
+ using namespace PatternMatch;
+ ICmpInst::Predicate Pred;
+ Value *LHS, *RHS;
+ const BasicBlock *IfTrue, *IfFalse;
+ // TODO: Handle switches.
+ if (!match(BB->getTerminator(),
+ m_Br(m_ICmp(Pred, m_Value(LHS), m_Value(RHS)),
+ m_BasicBlock(IfTrue), m_BasicBlock(IfFalse)))) {
+ MarkAllSuccessorsLive(BB);
+ continue;
+ }
+
+ if (!SE.isSCEVable(LHS->getType())) {
+ MarkAllSuccessorsLive(BB);
+ continue;
+ }
+
+ // Can we prove constant true or false for this condition?
+ const SCEV *LHSS = getSCEVOnFirstIteration(LHS, L, SE, FirstIterSCEV);
+ const SCEV *RHSS = getSCEVOnFirstIteration(RHS, L, SE, FirstIterSCEV);
+ if (SE.isKnownPredicate(Pred, LHSS, RHSS))
+ MarkLiveEdge(BB, BB->getTerminator()->getSuccessor(0));
+ else if (SE.isKnownPredicate(ICmpInst::getInversePredicate(Pred), LHSS,
+ RHSS))
+ MarkLiveEdge(BB, BB->getTerminator()->getSuccessor(1));
+ else
+ MarkAllSuccessorsLive(BB);
+ }
+
+ // We can break the latch if it wasn't live.
+ return !LiveEdges.count({ Latch, Header });
+}
+
/// If we can prove the backedge is untaken, remove it. This destroys the
/// loop, but leaves the (now trivially loop invariant) control flow and
/// side effects (if any) in place.
@@ -148,7 +298,7 @@ breakBackedgeIfNotTaken(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
return LoopDeletionResult::Unmodified;
auto *BTC = SE.getBackedgeTakenCount(L);
- if (!BTC->isZero())
+ if (!BTC->isZero() && !canProveExitOnFirstIteration(L, DT, SE, LI))
return LoopDeletionResult::Unmodified;
breakLoopBackedge(L, DT, SE, LI, MSSA);
diff --git a/llvm/test/Transforms/LoopDeletion/eval_first_iteration.ll b/llvm/test/Transforms/LoopDeletion/eval_first_iteration.ll
index 98dafebe0df02..aa3bfb062ccfd 100644
--- a/llvm/test/Transforms/LoopDeletion/eval_first_iteration.ll
+++ b/llvm/test/Transforms/LoopDeletion/eval_first_iteration.ll
@@ -7,7 +7,6 @@
; and therefore prove that %sum.next = %sum + %sub = %sum + %limit - %sum = %limit,
; and predicate is false.
-; TODO: We can break the backedge here.
define i32 @test_ne(i32 %limit) {
; CHECK-LABEL: @test_ne(
; CHECK-NEXT: entry:
@@ -60,7 +59,6 @@ failure:
unreachable
}
-; TODO: We can break the backedge here.
define i32 @test_slt(i32 %limit) {
; CHECK-LABEL: @test_slt(
; CHECK-NEXT: entry:
@@ -113,7 +111,6 @@ failure:
unreachable
}
-; TODO: We can break the backedge here.
define i32 @test_ult(i32 %limit) {
; CHECK-LABEL: @test_ult(
; CHECK-NEXT: entry:
@@ -166,7 +163,6 @@ failure:
unreachable
}
-; TODO: We can break the backedge here.
define i32 @test_sgt(i32 %limit) {
; CHECK-LABEL: @test_sgt(
; CHECK-NEXT: entry:
@@ -219,7 +215,6 @@ failure:
unreachable
}
-; TODO: We can break the backedge here.
define i32 @test_ugt(i32 %limit) {
; CHECK-LABEL: @test_ugt(
; CHECK-NEXT: entry:
@@ -272,7 +267,6 @@ failure:
unreachable
}
-; TODO: We can break the backedge here.
define i32 @test_multiple_pred(i32 %limit) {
; CHECK-LABEL: @test_multiple_pred(
; CHECK-NEXT: entry:
@@ -344,17 +338,19 @@ define i32 @test_ne_const() {
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
-; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[SUM_NEXT:%.*]], [[BACKEDGE:%.*]] ]
+; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: [[SUB:%.*]] = sub i32 4, [[SUM]]
; CHECK-NEXT: [[IS_POSITIVE:%.*]] = icmp sgt i32 [[SUB]], 0
-; CHECK-NEXT: br i1 [[IS_POSITIVE]], label [[BACKEDGE]], label [[IF_FALSE:%.*]]
+; CHECK-NEXT: br i1 [[IS_POSITIVE]], label [[BACKEDGE:%.*]], label [[IF_FALSE:%.*]]
; CHECK: if.false:
; CHECK-NEXT: br label [[BACKEDGE]]
; CHECK: backedge:
; CHECK-NEXT: [[MERGE_PHI:%.*]] = phi i32 [ 0, [[IF_FALSE]] ], [ [[SUB]], [[LOOP]] ]
-; CHECK-NEXT: [[SUM_NEXT]] = add i32 [[SUM]], [[MERGE_PHI]]
+; CHECK-NEXT: [[SUM_NEXT:%.*]] = add i32 [[SUM]], [[MERGE_PHI]]
; CHECK-NEXT: [[LOOP_COND:%.*]] = icmp ne i32 [[SUM_NEXT]], 4
-; CHECK-NEXT: br i1 [[LOOP_COND]], label [[LOOP]], label [[DONE:%.*]]
+; CHECK-NEXT: br i1 [[LOOP_COND]], label [[BACKEDGE_LOOP_CRIT_EDGE:%.*]], label [[DONE:%.*]]
+; CHECK: backedge.loop_crit_edge:
+; CHECK-NEXT: unreachable
; CHECK: done:
; CHECK-NEXT: [[SUM_NEXT_LCSSA:%.*]] = phi i32 [ [[SUM_NEXT]], [[BACKEDGE]] ]
; CHECK-NEXT: ret i32 [[SUM_NEXT_LCSSA]]
@@ -394,17 +390,19 @@ define i32 @test_slt_const() {
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
-; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[SUM_NEXT:%.*]], [[BACKEDGE:%.*]] ]
+; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: [[SUB:%.*]] = sub i32 4, [[SUM]]
; CHECK-NEXT: [[IS_POSITIVE:%.*]] = icmp sgt i32 [[SUB]], 0
-; CHECK-NEXT: br i1 [[IS_POSITIVE]], label [[BACKEDGE]], label [[IF_FALSE:%.*]]
+; CHECK-NEXT: br i1 [[IS_POSITIVE]], label [[BACKEDGE:%.*]], label [[IF_FALSE:%.*]]
; CHECK: if.false:
; CHECK-NEXT: br label [[BACKEDGE]]
; CHECK: backedge:
; CHECK-NEXT: [[MERGE_PHI:%.*]] = phi i32 [ 0, [[IF_FALSE]] ], [ [[SUB]], [[LOOP]] ]
-; CHECK-NEXT: [[SUM_NEXT]] = add i32 [[SUM]], [[MERGE_PHI]]
+; CHECK-NEXT: [[SUM_NEXT:%.*]] = add i32 [[SUM]], [[MERGE_PHI]]
; CHECK-NEXT: [[LOOP_COND:%.*]] = icmp slt i32 [[SUM_NEXT]], 4
-; CHECK-NEXT: br i1 [[LOOP_COND]], label [[LOOP]], label [[DONE:%.*]]
+; CHECK-NEXT: br i1 [[LOOP_COND]], label [[BACKEDGE_LOOP_CRIT_EDGE:%.*]], label [[DONE:%.*]]
+; CHECK: backedge.loop_crit_edge:
+; CHECK-NEXT: unreachable
; CHECK: done:
; CHECK-NEXT: [[SUM_NEXT_LCSSA:%.*]] = phi i32 [ [[SUM_NEXT]], [[BACKEDGE]] ]
; CHECK-NEXT: ret i32 [[SUM_NEXT_LCSSA]]
@@ -444,17 +442,19 @@ define i32 @test_ult_const() {
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
-; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[SUM_NEXT:%.*]], [[BACKEDGE:%.*]] ]
+; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: [[SUB:%.*]] = sub i32 4, [[SUM]]
; CHECK-NEXT: [[IS_POSITIVE:%.*]] = icmp sgt i32 [[SUB]], 0
-; CHECK-NEXT: br i1 [[IS_POSITIVE]], label [[BACKEDGE]], label [[IF_FALSE:%.*]]
+; CHECK-NEXT: br i1 [[IS_POSITIVE]], label [[BACKEDGE:%.*]], label [[IF_FALSE:%.*]]
; CHECK: if.false:
; CHECK-NEXT: br label [[BACKEDGE]]
; CHECK: backedge:
; CHECK-NEXT: [[MERGE_PHI:%.*]] = phi i32 [ 0, [[IF_FALSE]] ], [ [[SUB]], [[LOOP]] ]
-; CHECK-NEXT: [[SUM_NEXT]] = add i32 [[SUM]], [[MERGE_PHI]]
+; CHECK-NEXT: [[SUM_NEXT:%.*]] = add i32 [[SUM]], [[MERGE_PHI]]
; CHECK-NEXT: [[LOOP_COND:%.*]] = icmp ult i32 [[SUM_NEXT]], 4
-; CHECK-NEXT: br i1 [[LOOP_COND]], label [[LOOP]], label [[DONE:%.*]]
+; CHECK-NEXT: br i1 [[LOOP_COND]], label [[BACKEDGE_LOOP_CRIT_EDGE:%.*]], label [[DONE:%.*]]
+; CHECK: backedge.loop_crit_edge:
+; CHECK-NEXT: unreachable
; CHECK: done:
; CHECK-NEXT: [[SUM_NEXT_LCSSA:%.*]] = phi i32 [ [[SUM_NEXT]], [[BACKEDGE]] ]
; CHECK-NEXT: ret i32 [[SUM_NEXT_LCSSA]]
@@ -494,17 +494,19 @@ define i32 @test_sgt_const() {
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
-; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[SUM_NEXT:%.*]], [[BACKEDGE:%.*]] ]
+; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: [[SUB:%.*]] = sub i32 4, [[SUM]]
; CHECK-NEXT: [[IS_POSITIVE:%.*]] = icmp sgt i32 [[SUB]], 0
-; CHECK-NEXT: br i1 [[IS_POSITIVE]], label [[BACKEDGE]], label [[IF_FALSE:%.*]]
+; CHECK-NEXT: br i1 [[IS_POSITIVE]], label [[BACKEDGE:%.*]], label [[IF_FALSE:%.*]]
; CHECK: if.false:
; CHECK-NEXT: br label [[BACKEDGE]]
; CHECK: backedge:
; CHECK-NEXT: [[MERGE_PHI:%.*]] = phi i32 [ 0, [[IF_FALSE]] ], [ [[SUB]], [[LOOP]] ]
-; CHECK-NEXT: [[SUM_NEXT]] = add i32 [[SUM]], [[MERGE_PHI]]
+; CHECK-NEXT: [[SUM_NEXT:%.*]] = add i32 [[SUM]], [[MERGE_PHI]]
; CHECK-NEXT: [[LOOP_COND:%.*]] = icmp sgt i32 [[SUM_NEXT]], 4
-; CHECK-NEXT: br i1 [[LOOP_COND]], label [[LOOP]], label [[DONE:%.*]]
+; CHECK-NEXT: br i1 [[LOOP_COND]], label [[BACKEDGE_LOOP_CRIT_EDGE:%.*]], label [[DONE:%.*]]
+; CHECK: backedge.loop_crit_edge:
+; CHECK-NEXT: unreachable
; CHECK: done:
; CHECK-NEXT: [[SUM_NEXT_LCSSA:%.*]] = phi i32 [ [[SUM_NEXT]], [[BACKEDGE]] ]
; CHECK-NEXT: ret i32 [[SUM_NEXT_LCSSA]]
@@ -544,17 +546,19 @@ define i32 @test_ugt_const() {
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
-; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[SUM_NEXT:%.*]], [[BACKEDGE:%.*]] ]
+; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: [[SUB:%.*]] = sub i32 4, [[SUM]]
; CHECK-NEXT: [[IS_POSITIVE:%.*]] = icmp sgt i32 [[SUB]], 0
-; CHECK-NEXT: br i1 [[IS_POSITIVE]], label [[BACKEDGE]], label [[IF_FALSE:%.*]]
+; CHECK-NEXT: br i1 [[IS_POSITIVE]], label [[BACKEDGE:%.*]], label [[IF_FALSE:%.*]]
; CHECK: if.false:
; CHECK-NEXT: br label [[BACKEDGE]]
; CHECK: backedge:
; CHECK-NEXT: [[MERGE_PHI:%.*]] = phi i32 [ 0, [[IF_FALSE]] ], [ [[SUB]], [[LOOP]] ]
-; CHECK-NEXT: [[SUM_NEXT]] = add i32 [[SUM]], [[MERGE_PHI]]
+; CHECK-NEXT: [[SUM_NEXT:%.*]] = add i32 [[SUM]], [[MERGE_PHI]]
; CHECK-NEXT: [[LOOP_COND:%.*]] = icmp ugt i32 [[SUM_NEXT]], 4
-; CHECK-NEXT: br i1 [[LOOP_COND]], label [[LOOP]], label [[DONE:%.*]]
+; CHECK-NEXT: br i1 [[LOOP_COND]], label [[BACKEDGE_LOOP_CRIT_EDGE:%.*]], label [[DONE:%.*]]
+; CHECK: backedge.loop_crit_edge:
+; CHECK-NEXT: unreachable
; CHECK: done:
; CHECK-NEXT: [[SUM_NEXT_LCSSA:%.*]] = phi i32 [ [[SUM_NEXT]], [[BACKEDGE]] ]
; CHECK-NEXT: ret i32 [[SUM_NEXT_LCSSA]]
@@ -594,22 +598,24 @@ define i32 @test_multiple_pred_const() {
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
-; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[SUM_NEXT:%.*]], [[BACKEDGE:%.*]] ]
+; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: [[SUB:%.*]] = sub i32 4, [[SUM]]
; CHECK-NEXT: [[IS_POSITIVE:%.*]] = icmp sgt i32 [[SUB]], 0
; CHECK-NEXT: br i1 [[IS_POSITIVE]], label [[IF_TRUE:%.*]], label [[IF_FALSE:%.*]]
; CHECK: if.true:
; CHECK-NEXT: switch i32 4, label [[FAILURE:%.*]] [
-; CHECK-NEXT: i32 100, label [[BACKEDGE]]
+; CHECK-NEXT: i32 100, label [[BACKEDGE:%.*]]
; CHECK-NEXT: i32 200, label [[BACKEDGE]]
; CHECK-NEXT: ]
; CHECK: if.false:
; CHECK-NEXT: br label [[BACKEDGE]]
; CHECK: backedge:
; CHECK-NEXT: [[MERGE_PHI:%.*]] = phi i32 [ 0, [[IF_FALSE]] ], [ [[SUB]], [[IF_TRUE]] ], [ [[SUB]], [[IF_TRUE]] ]
-; CHECK-NEXT: [[SUM_NEXT]] = add i32 [[SUM]], [[MERGE_PHI]]
+; CHECK-NEXT: [[SUM_NEXT:%.*]] = add i32 [[SUM]], [[MERGE_PHI]]
; CHECK-NEXT: [[LOOP_COND:%.*]] = icmp ne i32 [[SUM_NEXT]], 4
-; CHECK-NEXT: br i1 [[LOOP_COND]], label [[LOOP]], label [[DONE:%.*]]
+; CHECK-NEXT: br i1 [[LOOP_COND]], label [[BACKEDGE_LOOP_CRIT_EDGE:%.*]], label [[DONE:%.*]]
+; CHECK: backedge.loop_crit_edge:
+; CHECK-NEXT: unreachable
; CHECK: done:
; CHECK-NEXT: [[SUM_NEXT_LCSSA:%.*]] = phi i32 [ [[SUM_NEXT]], [[BACKEDGE]] ]
; CHECK-NEXT: ret i32 [[SUM_NEXT_LCSSA]]
diff --git a/llvm/test/Transforms/LoopDeletion/zero-btc.ll b/llvm/test/Transforms/LoopDeletion/zero-btc.ll
index 413b0a877dd48..958de0505af7f 100644
--- a/llvm/test/Transforms/LoopDeletion/zero-btc.ll
+++ b/llvm/test/Transforms/LoopDeletion/zero-btc.ll
@@ -161,14 +161,16 @@ define void @test_multi_exit3(i1 %cond1) {
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
-; CHECK-NEXT: [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_INC:%.*]], [[LATCH:%.*]] ]
+; CHECK-NEXT: [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: store i32 0, i32* @G, align 4
-; CHECK-NEXT: br i1 [[COND1:%.*]], label [[LATCH]], label [[EXIT:%.*]]
+; CHECK-NEXT: br i1 [[COND1:%.*]], label [[LATCH:%.*]], label [[EXIT:%.*]]
; CHECK: latch:
; CHECK-NEXT: store i32 1, i32* @G, align 4
-; CHECK-NEXT: [[IV_INC]] = add i32 [[IV]], 1
+; CHECK-NEXT: [[IV_INC:%.*]] = add i32 [[IV]], 1
; CHECK-NEXT: [[BE_TAKEN:%.*]] = icmp ne i32 [[IV_INC]], 1
-; CHECK-NEXT: br i1 [[BE_TAKEN]], label [[LOOP]], label [[EXIT]]
+; CHECK-NEXT: br i1 [[BE_TAKEN]], label [[LATCH_LOOP_CRIT_EDGE:%.*]], label [[EXIT]]
+; CHECK: latch.loop_crit_edge:
+; CHECK-NEXT: unreachable
; CHECK: exit:
; CHECK-NEXT: ret void
;
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