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Revert "Return "[LoopDeletion] Break backedge if we can prove that th…
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…e loop is exited on 1st iteration""

This reverts commit 43d2e51.

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@xortator
xortator committed May 26, 2021
1 parent 43d2e51 commit 0de553d
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152 changes: 1 addition & 151 deletions llvm/lib/Transforms/Scalar/LoopDeletion.cpp
View file
Expand Up @@ -17,7 +17,6 @@
#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"
Expand Down Expand Up @@ -136,155 +135,6 @@ 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.
Expand All @@ -298,7 +148,7 @@ breakBackedgeIfNotTaken(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
return LoopDeletionResult::Unmodified;

auto *BTC = SE.getBackedgeTakenCount(L);
if (!BTC->isZero() && !canProveExitOnFirstIteration(L, DT, SE, LI))
if (!BTC->isZero())
return LoopDeletionResult::Unmodified;

breakLoopBackedge(L, DT, SE, LI, MSSA);
Expand Down
66 changes: 30 additions & 36 deletions llvm/test/Transforms/LoopDeletion/eval_first_iteration.ll
View file
Expand Up @@ -7,6 +7,7 @@
; 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:
Expand Down Expand Up @@ -59,6 +60,7 @@ failure:
unreachable
}

; TODO: We can break the backedge here.
define i32 @test_slt(i32 %limit) {
; CHECK-LABEL: @test_slt(
; CHECK-NEXT: entry:
Expand Down Expand Up @@ -111,6 +113,7 @@ failure:
unreachable
}

; TODO: We can break the backedge here.
define i32 @test_ult(i32 %limit) {
; CHECK-LABEL: @test_ult(
; CHECK-NEXT: entry:
Expand Down Expand Up @@ -163,6 +166,7 @@ failure:
unreachable
}

; TODO: We can break the backedge here.
define i32 @test_sgt(i32 %limit) {
; CHECK-LABEL: @test_sgt(
; CHECK-NEXT: entry:
Expand Down Expand Up @@ -215,6 +219,7 @@ failure:
unreachable
}

; TODO: We can break the backedge here.
define i32 @test_ugt(i32 %limit) {
; CHECK-LABEL: @test_ugt(
; CHECK-NEXT: entry:
Expand Down Expand Up @@ -267,6 +272,7 @@ failure:
unreachable
}

; TODO: We can break the backedge here.
define i32 @test_multiple_pred(i32 %limit) {
; CHECK-LABEL: @test_multiple_pred(
; CHECK-NEXT: entry:
Expand Down Expand Up @@ -338,19 +344,17 @@ define i32 @test_ne_const() {
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[SUM_NEXT:%.*]], [[BACKEDGE:%.*]] ]
; 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 [[BACKEDGE_LOOP_CRIT_EDGE:%.*]], label [[DONE:%.*]]
; CHECK: backedge.loop_crit_edge:
; CHECK-NEXT: unreachable
; CHECK-NEXT: br i1 [[LOOP_COND]], label [[LOOP]], label [[DONE:%.*]]
; CHECK: done:
; CHECK-NEXT: [[SUM_NEXT_LCSSA:%.*]] = phi i32 [ [[SUM_NEXT]], [[BACKEDGE]] ]
; CHECK-NEXT: ret i32 [[SUM_NEXT_LCSSA]]
Expand Down Expand Up @@ -390,19 +394,17 @@ define i32 @test_slt_const() {
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[SUM_NEXT:%.*]], [[BACKEDGE:%.*]] ]
; 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 [[BACKEDGE_LOOP_CRIT_EDGE:%.*]], label [[DONE:%.*]]
; CHECK: backedge.loop_crit_edge:
; CHECK-NEXT: unreachable
; CHECK-NEXT: br i1 [[LOOP_COND]], label [[LOOP]], label [[DONE:%.*]]
; CHECK: done:
; CHECK-NEXT: [[SUM_NEXT_LCSSA:%.*]] = phi i32 [ [[SUM_NEXT]], [[BACKEDGE]] ]
; CHECK-NEXT: ret i32 [[SUM_NEXT_LCSSA]]
Expand Down Expand Up @@ -442,19 +444,17 @@ define i32 @test_ult_const() {
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[SUM_NEXT:%.*]], [[BACKEDGE:%.*]] ]
; 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 [[BACKEDGE_LOOP_CRIT_EDGE:%.*]], label [[DONE:%.*]]
; CHECK: backedge.loop_crit_edge:
; CHECK-NEXT: unreachable
; CHECK-NEXT: br i1 [[LOOP_COND]], label [[LOOP]], label [[DONE:%.*]]
; CHECK: done:
; CHECK-NEXT: [[SUM_NEXT_LCSSA:%.*]] = phi i32 [ [[SUM_NEXT]], [[BACKEDGE]] ]
; CHECK-NEXT: ret i32 [[SUM_NEXT_LCSSA]]
Expand Down Expand Up @@ -494,19 +494,17 @@ define i32 @test_sgt_const() {
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[SUM_NEXT:%.*]], [[BACKEDGE:%.*]] ]
; 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 [[BACKEDGE_LOOP_CRIT_EDGE:%.*]], label [[DONE:%.*]]
; CHECK: backedge.loop_crit_edge:
; CHECK-NEXT: unreachable
; CHECK-NEXT: br i1 [[LOOP_COND]], label [[LOOP]], label [[DONE:%.*]]
; CHECK: done:
; CHECK-NEXT: [[SUM_NEXT_LCSSA:%.*]] = phi i32 [ [[SUM_NEXT]], [[BACKEDGE]] ]
; CHECK-NEXT: ret i32 [[SUM_NEXT_LCSSA]]
Expand Down Expand Up @@ -546,19 +544,17 @@ define i32 @test_ugt_const() {
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[SUM_NEXT:%.*]], [[BACKEDGE:%.*]] ]
; 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 [[BACKEDGE_LOOP_CRIT_EDGE:%.*]], label [[DONE:%.*]]
; CHECK: backedge.loop_crit_edge:
; CHECK-NEXT: unreachable
; CHECK-NEXT: br i1 [[LOOP_COND]], label [[LOOP]], label [[DONE:%.*]]
; CHECK: done:
; CHECK-NEXT: [[SUM_NEXT_LCSSA:%.*]] = phi i32 [ [[SUM_NEXT]], [[BACKEDGE]] ]
; CHECK-NEXT: ret i32 [[SUM_NEXT_LCSSA]]
Expand Down Expand Up @@ -598,24 +594,22 @@ define i32 @test_multiple_pred_const() {
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[SUM_NEXT:%.*]], [[BACKEDGE:%.*]] ]
; 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 [[BACKEDGE_LOOP_CRIT_EDGE:%.*]], label [[DONE:%.*]]
; CHECK: backedge.loop_crit_edge:
; CHECK-NEXT: unreachable
; CHECK-NEXT: br i1 [[LOOP_COND]], label [[LOOP]], label [[DONE:%.*]]
; CHECK: done:
; CHECK-NEXT: [[SUM_NEXT_LCSSA:%.*]] = phi i32 [ [[SUM_NEXT]], [[BACKEDGE]] ]
; CHECK-NEXT: ret i32 [[SUM_NEXT_LCSSA]]
Expand Down
10 changes: 4 additions & 6 deletions llvm/test/Transforms/LoopDeletion/zero-btc.ll
View file
Expand Up @@ -161,16 +161,14 @@ define void @test_multi_exit3(i1 %cond1) {
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_INC:%.*]], [[LATCH:%.*]] ]
; 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 [[LATCH_LOOP_CRIT_EDGE:%.*]], label [[EXIT]]
; CHECK: latch.loop_crit_edge:
; CHECK-NEXT: unreachable
; CHECK-NEXT: br i1 [[BE_TAKEN]], label [[LOOP]], label [[EXIT]]
; CHECK: exit:
; CHECK-NEXT: ret void
;
Expand Down

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