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[LoopDeletion] Handle switch in proving that loop exits on first iteration
Added check for switch-terminated blocks in loops. Now if a block is terminated with a switch, we try to find out which of the cases is taken on 1st iteration and mark corresponding edge from the block to the case successor as live. Patch by Dmitry Makogon! Differential Revision: https://reviews.llvm.org/D105688 Reviewed By: nikic, mkazantsev
This commit is contained in:
Max Kazantsev
parent
fd61052e59
commit
974341bf3b
@ -318,53 +318,63 @@ static bool canProveExitOnFirstIteration(Loop *L, DominatorTree &DT,
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Value *LHS, *RHS;
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BasicBlock *IfTrue, *IfFalse;
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auto *Term = BB->getTerminator();
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// TODO: Handle switch.
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if (!match(Term, m_Br(m_ICmp(Pred, m_Value(LHS), m_Value(RHS)),
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m_BasicBlock(IfTrue), m_BasicBlock(IfFalse)))) {
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MarkAllSuccessorsLive(BB);
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continue;
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}
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if (match(Term, m_Br(m_ICmp(Pred, m_Value(LHS), m_Value(RHS)),
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m_BasicBlock(IfTrue), m_BasicBlock(IfFalse)))) {
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if (!LHS->getType()->isIntegerTy()) {
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MarkAllSuccessorsLive(BB);
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continue;
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}
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if (!LHS->getType()->isIntegerTy()) {
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MarkAllSuccessorsLive(BB);
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continue;
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}
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// Can we prove constant true or false for this condition?
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LHS = getValueOnFirstIteration(LHS, FirstIterValue, SQ);
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RHS = getValueOnFirstIteration(RHS, FirstIterValue, SQ);
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auto *KnownCondition = SimplifyICmpInst(Pred, LHS, RHS, SQ);
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if (!KnownCondition) {
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// Failed to simplify.
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MarkAllSuccessorsLive(BB);
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continue;
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}
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if (isa<UndefValue>(KnownCondition)) {
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// TODO: According to langref, branching by undef is undefined behavior.
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// It means that, theoretically, we should be able to just continue
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// without marking any successors as live. However, we are not certain
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// how correct our compiler is at handling such cases. So we are being
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// very conservative here.
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//
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// If there is a non-loop successor, always assume this branch leaves the
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// loop. Otherwise, arbitrarily take IfTrue.
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//
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// Once we are certain that branching by undef is handled correctly by
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// other transforms, we should not mark any successors live here.
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if (L->contains(IfTrue) && L->contains(IfFalse))
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// Can we prove constant true or false for this condition?
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LHS = getValueOnFirstIteration(LHS, FirstIterValue, SQ);
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RHS = getValueOnFirstIteration(RHS, FirstIterValue, SQ);
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auto *KnownCondition = SimplifyICmpInst(Pred, LHS, RHS, SQ);
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if (!KnownCondition) {
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// Failed to simplify.
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MarkAllSuccessorsLive(BB);
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continue;
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}
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if (isa<UndefValue>(KnownCondition)) {
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// TODO: According to langref, branching by undef is undefined behavior.
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// It means that, theoretically, we should be able to just continue
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// without marking any successors as live. However, we are not certain
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// how correct our compiler is at handling such cases. So we are being
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// very conservative here.
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//
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// If there is a non-loop successor, always assume this branch leaves the
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// loop. Otherwise, arbitrarily take IfTrue.
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//
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// Once we are certain that branching by undef is handled correctly by
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// other transforms, we should not mark any successors live here.
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if (L->contains(IfTrue) && L->contains(IfFalse))
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MarkLiveEdge(BB, IfTrue);
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continue;
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}
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auto *ConstCondition = dyn_cast<ConstantInt>(KnownCondition);
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if (!ConstCondition) {
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// Non-constant condition, cannot analyze any further.
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MarkAllSuccessorsLive(BB);
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continue;
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}
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if (ConstCondition->isAllOnesValue())
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MarkLiveEdge(BB, IfTrue);
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continue;
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}
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auto *ConstCondition = dyn_cast<ConstantInt>(KnownCondition);
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if (!ConstCondition) {
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// Non-constant condition, cannot analyze any further.
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else
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MarkLiveEdge(BB, IfFalse);
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} else if (SwitchInst *SI = dyn_cast<SwitchInst>(Term)) {
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auto *SwitchValue = SI->getCondition();
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auto *SwitchValueOnFirstIter =
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getValueOnFirstIteration(SwitchValue, FirstIterValue, SQ);
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auto *ConstSwitchValue = dyn_cast<ConstantInt>(SwitchValueOnFirstIter);
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if (!ConstSwitchValue) {
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MarkAllSuccessorsLive(BB);
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continue;
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}
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auto CaseIterator = SI->findCaseValue(ConstSwitchValue);
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MarkLiveEdge(BB, CaseIterator->getCaseSuccessor());
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} else {
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MarkAllSuccessorsLive(BB);
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continue;
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}
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if (ConstCondition->isAllOnesValue())
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MarkLiveEdge(BB, IfTrue);
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else
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MarkLiveEdge(BB, IfFalse);
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}
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// We can break the latch if it wasn't live.
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@ -1057,7 +1057,7 @@ define i32 @test_switch_ne_default() {
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; CHECK-NEXT: entry:
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; CHECK-NEXT: br label [[LOOP:%.*]]
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; CHECK: loop:
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; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[SUM_NEXT:%.*]], [[BACKEDGE:%.*]] ]
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; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ]
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; CHECK-NEXT: [[SUB:%.*]] = sub i32 4, [[SUM]]
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; CHECK-NEXT: switch i32 [[SUB]], label [[DEFAULT:%.*]] [
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; CHECK-NEXT: i32 0, label [[ONZERO:%.*]]
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@ -1065,7 +1065,7 @@ define i32 @test_switch_ne_default() {
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; CHECK-NEXT: i32 2, label [[ONTWO:%.*]]
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; CHECK-NEXT: ]
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; CHECK: default:
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; CHECK-NEXT: br label [[BACKEDGE]]
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; CHECK-NEXT: br label [[BACKEDGE:%.*]]
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; CHECK: onzero:
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; CHECK-NEXT: br label [[BACKEDGE]]
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; CHECK: onone:
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@ -1074,9 +1074,11 @@ define i32 @test_switch_ne_default() {
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; CHECK-NEXT: br label [[BACKEDGE]]
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; CHECK: backedge:
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; CHECK-NEXT: [[MERGE_PHI:%.*]] = phi i32 [ [[SUB]], [[DEFAULT]] ], [ 0, [[ONZERO]] ], [ 1, [[ONONE]] ], [ 2, [[ONTWO]] ]
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; CHECK-NEXT: [[SUM_NEXT]] = add i32 [[SUM]], [[MERGE_PHI]]
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; CHECK-NEXT: [[SUM_NEXT:%.*]] = add i32 [[SUM]], [[MERGE_PHI]]
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; CHECK-NEXT: [[LOOP_COND:%.*]] = icmp ne i32 [[SUM_NEXT]], 4
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; CHECK-NEXT: br i1 [[LOOP_COND]], label [[LOOP]], label [[DONE:%.*]]
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; CHECK-NEXT: br i1 [[LOOP_COND]], label [[BACKEDGE_LOOP_CRIT_EDGE:%.*]], label [[DONE:%.*]]
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; CHECK: backedge.loop_crit_edge:
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; CHECK-NEXT: unreachable
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; CHECK: done:
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; CHECK-NEXT: [[SUM_NEXT_LCSSA:%.*]] = phi i32 [ [[SUM_NEXT]], [[BACKEDGE]] ]
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; CHECK-NEXT: ret i32 [[SUM_NEXT_LCSSA]]
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@ -1122,7 +1124,7 @@ define i32 @test_switch_ne_one_case() {
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; CHECK-NEXT: entry:
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; CHECK-NEXT: br label [[LOOP:%.*]]
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; CHECK: loop:
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; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[SUM_NEXT:%.*]], [[BACKEDGE:%.*]] ]
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; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ]
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; CHECK-NEXT: [[SUB:%.*]] = sub i32 4, [[SUM]]
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; CHECK-NEXT: switch i32 [[SUB]], label [[DEFAULT:%.*]] [
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; CHECK-NEXT: i32 0, label [[ONZERO:%.*]]
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@ -1130,7 +1132,7 @@ define i32 @test_switch_ne_one_case() {
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; CHECK-NEXT: i32 4, label [[ONTWO:%.*]]
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; CHECK-NEXT: ]
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; CHECK: default:
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; CHECK-NEXT: br label [[BACKEDGE]]
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; CHECK-NEXT: br label [[BACKEDGE:%.*]]
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; CHECK: onzero:
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; CHECK-NEXT: br label [[BACKEDGE]]
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; CHECK: onone:
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@ -1139,9 +1141,11 @@ define i32 @test_switch_ne_one_case() {
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; CHECK-NEXT: br label [[BACKEDGE]]
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; CHECK: backedge:
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; CHECK-NEXT: [[MERGE_PHI:%.*]] = phi i32 [ 2, [[DEFAULT]] ], [ 0, [[ONZERO]] ], [ 1, [[ONONE]] ], [ [[SUB]], [[ONTWO]] ]
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; CHECK-NEXT: [[SUM_NEXT]] = add i32 [[SUM]], [[MERGE_PHI]]
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; CHECK-NEXT: [[SUM_NEXT:%.*]] = add i32 [[SUM]], [[MERGE_PHI]]
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; CHECK-NEXT: [[LOOP_COND:%.*]] = icmp ne i32 [[SUM_NEXT]], 4
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; CHECK-NEXT: br i1 [[LOOP_COND]], label [[LOOP]], label [[DONE:%.*]]
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; CHECK-NEXT: br i1 [[LOOP_COND]], label [[BACKEDGE_LOOP_CRIT_EDGE:%.*]], label [[DONE:%.*]]
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; CHECK: backedge.loop_crit_edge:
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; CHECK-NEXT: unreachable
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; CHECK: done:
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; CHECK-NEXT: [[SUM_NEXT_LCSSA:%.*]] = phi i32 [ [[SUM_NEXT]], [[BACKEDGE]] ]
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; CHECK-NEXT: ret i32 [[SUM_NEXT_LCSSA]]
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@ -1187,11 +1191,11 @@ define i32 @test_switch_ne_one_case_identical_jumps() {
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; CHECK-NEXT: entry:
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; CHECK-NEXT: br label [[LOOP:%.*]]
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; CHECK: loop:
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; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[SUM_NEXT:%.*]], [[BACKEDGE:%.*]] ]
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; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ]
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; CHECK-NEXT: [[SUB:%.*]] = sub i32 2, [[SUM]]
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; CHECK-NEXT: switch i32 [[SUB]], label [[DEFAULT:%.*]] [
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; CHECK-NEXT: i32 0, label [[FIRST_BLOCK:%.*]]
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; CHECK-NEXT: i32 1, label [[BACKEDGE]]
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; CHECK-NEXT: i32 1, label [[BACKEDGE:%.*]]
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; CHECK-NEXT: i32 2, label [[BACKEDGE]]
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; CHECK-NEXT: ]
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; CHECK: default:
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@ -1200,9 +1204,11 @@ define i32 @test_switch_ne_one_case_identical_jumps() {
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; CHECK-NEXT: br label [[BACKEDGE]]
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; CHECK: backedge:
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; CHECK-NEXT: [[MERGE_PHI:%.*]] = phi i32 [ 0, [[DEFAULT]] ], [ 1, [[FIRST_BLOCK]] ], [ [[SUB]], [[LOOP]] ], [ [[SUB]], [[LOOP]] ]
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; CHECK-NEXT: [[SUM_NEXT]] = add i32 [[SUM]], [[MERGE_PHI]]
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; CHECK-NEXT: [[SUM_NEXT:%.*]] = add i32 [[SUM]], [[MERGE_PHI]]
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; CHECK-NEXT: [[LOOP_COND:%.*]] = icmp ne i32 [[SUM_NEXT]], 2
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; CHECK-NEXT: br i1 [[LOOP_COND]], label [[LOOP]], label [[DONE:%.*]]
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; CHECK-NEXT: br i1 [[LOOP_COND]], label [[BACKEDGE_LOOP_CRIT_EDGE:%.*]], label [[DONE:%.*]]
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; CHECK: backedge.loop_crit_edge:
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; CHECK-NEXT: unreachable
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; CHECK: done:
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; CHECK-NEXT: [[SUM_NEXT_LCSSA:%.*]] = phi i32 [ [[SUM_NEXT]], [[BACKEDGE]] ]
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; CHECK-NEXT: ret i32 [[SUM_NEXT_LCSSA]]
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