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Revert "[LoopDeletion] Handle Phis with similar inputs from different blocks"

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This reverts commit bb1dc876ebb8a2eef38d5183d00c2db1437f1c91.

This patch causes an assertion failure when building an arm64 defconfig
Linux kernel.

See https://reviews.llvm.org/D103959 for a link to the original bug
report and a reduced reproducer.
This commit is contained in:
Nathan Chancellor 2021-06-21 10:18:55 -07:00
parent 7f56d08fc8
commit b329f1bc69
2 changed files with 28 additions and 30 deletions
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47
lib/Transforms/Scalar/LoopDeletion.cpp
View File

@ -245,25 +245,23 @@ static bool canProveExitOnFirstIteration(Loop *L, DominatorTree &DT,
MarkLiveEdge(BB, Succ);
};
// Check if there is only one value coming from all live predecessor blocks.
// Note that because we iterate in RPOT, we have already visited all its
// (non-latch) predecessors.
auto GetSoleInputOnFirstIteration = [&](PHINode & PN)->Value * {
BasicBlock *BB = PN.getParent();
// 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 PN.getIncomingValueForBlock(L->getLoopPredecessor());
Value *OnlyInput = nullptr;
return L->getLoopPredecessor();
BasicBlock *OnlyPred = nullptr;
for (auto *Pred : predecessors(BB))
if (LiveEdges.count({ Pred, BB })) {
Value *Incoming = PN.getIncomingValueForBlock(Pred);
// Two inputs.
if (OnlyInput && OnlyInput != Incoming)
if (OnlyPred != Pred && LiveEdges.count({ Pred, BB })) {
// 2 live preds.
if (OnlyPred)
return nullptr;
OnlyInput = Incoming;
OnlyPred = Pred;
}
assert(OnlyInput && "No live predecessors?");
return OnlyInput;
assert(OnlyPred && "No live predecessors?");
return OnlyPred;
};
DenseMap<Value *, Value *> FirstIterValue;
@ -292,17 +290,18 @@ static bool canProveExitOnFirstIteration(Loop *L, DominatorTree &DT,
continue;
}
// If Phi has only one input from all live input blocks, use it.
for (auto &PN : BB->phis()) {
if (!PN.getType()->isIntegerTy())
continue;
auto *Incoming = GetSoleInputOnFirstIteration(PN);
if (Incoming && DT.dominates(Incoming, BB->getTerminator())) {
Value *FirstIterV =
getValueOnFirstIteration(Incoming, FirstIterValue, SQ);
FirstIterValue[&PN] = FirstIterV;
// 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 (!PN.getType()->isIntegerTy())
continue;
auto *Incoming = PN.getIncomingValueForBlock(OnlyPred);
if (DT.dominates(Incoming, BB->getTerminator())) {
Value *FirstIterV =
getValueOnFirstIteration(Incoming, FirstIterValue, SQ);
FirstIterValue[&PN] = FirstIterV;
}
}
}
using namespace PatternMatch;
ICmpInst::Predicate Pred;

11
test/Transforms/LoopDeletion/eval_first_iteration.ll
View File

@ -655,19 +655,20 @@ failure:
unreachable
}
; TODO: We can break the backedge here.
define i32 @test_multiple_pred_2() {
; CHECK-LABEL: @test_multiple_pred_2(
; 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: br i1 undef, label [[IF_TRUE_1:%.*]], label [[IF_TRUE_2:%.*]]
; CHECK: if.true.1:
; CHECK-NEXT: br label [[BACKEDGE:%.*]]
; CHECK-NEXT: br label [[BACKEDGE]]
; CHECK: if.true.2:
; CHECK-NEXT: br label [[BACKEDGE]]
; CHECK: if.false:
@ -678,11 +679,9 @@ define i32 @test_multiple_pred_2() {
; CHECK-NEXT: br label [[BACKEDGE]]
; CHECK: backedge:
; CHECK-NEXT: [[MERGE_PHI:%.*]] = phi i32 [ 0, [[IF_FALSE_1]] ], [ 0, [[IF_FALSE_2]] ], [ [[SUB]], [[IF_TRUE_1]] ], [ [[SUB]], [[IF_TRUE_2]] ]
; 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]]