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[SimpleLoopUnswitch] Add non-empty unreachable block check to exit cases removed.

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Summary:
Update check to include the check for unreachable.

Basic blocks ending in unreachable are special cased, as these blocks may be already unswitched. Before this patch this check is only done for the default destination.
The condition for the exit cases and the default case must be the same, because we should never leave edges from the switch instruction to a basic block that we are unswitching. In PR45355 we still have a remaining edge (that we're attempting to remove from the DT) because its the default edge to an unreachable-terminated block where we unswitch a case edge to that block.

Resolves PR45355.

Reviewers: chandlerc

Subscribers: hiraditya, uabelho, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D78279
This commit is contained in:
Alina Sbirlea 2020-04-16 00:08:53 -07:00
parent e34f4b618f
commit 6374154cba
2 changed files with 92 additions and 6 deletions
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12
lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
View File

@ -598,6 +598,11 @@ static bool unswitchTrivialSwitch(Loop &L, SwitchInst &SI, DominatorTree &DT,
auto *ParentBB = SI.getParent();
// The same check must be used both for the default and the exit cases. We
// should never leave edges from the switch instruction to a basic block that
// we are unswitching, hence the condition used to determine the default case
// needs to also be used to populate ExitCaseIndices, which is then used to
// remove cases from the switch.
auto IsTriviallyUnswitchableExitBlock = [&](BasicBlock &BBToCheck) {
// BBToCheck is not an exit block if it is inside loop L.
if (L.contains(&BBToCheck))
@ -616,12 +621,9 @@ static bool unswitchTrivialSwitch(Loop &L, SwitchInst &SI, DominatorTree &DT,
};
SmallVector<int, 4> ExitCaseIndices;
for (auto Case : SI.cases()) {
auto *SuccBB = Case.getCaseSuccessor();
if (!L.contains(SuccBB) &&
areLoopExitPHIsLoopInvariant(L, *ParentBB, *SuccBB))
for (auto Case : SI.cases())
if (IsTriviallyUnswitchableExitBlock(*Case.getCaseSuccessor()))
ExitCaseIndices.push_back(Case.getCaseIndex());
}
BasicBlock *DefaultExitBB = nullptr;
SwitchInstProfUpdateWrapper::CaseWeightOpt DefaultCaseWeight =
SwitchInstProfUpdateWrapper::getSuccessorWeight(SI, 0);

86
test/Transforms/SimpleLoopUnswitch/trivial-unswitch.ll
View File

@ -1274,14 +1274,67 @@ NonEmptyUnreachableBlock:
; CHECK-NEXT: %cleanup.dest.slot.0 = select i1 undef, i32 5, i32 undef
; CHECK-NEXT: switch i32 %cleanup.dest.slot.0, label %NonEmptyUnreachableBlock [
; CHECK-NEXT: i32 1, label %NonEmptyUnreachableBlock
; CHECK-NEXT: i32 2, label %loop.loopexit
; CHECK-NEXT: i32 0, label %loop.split
; CHECK-NEXT: i32 2, label %loop.split
; CHECK-NEXT: ]
; CHECK:loop.split:
; CHECK-NEXT: br label %for.cond
; CHECK:for.cond:
; CHECK-NEXT: switch i32 %cleanup.dest.slot.0, label %loop.loopexit [
; CHECK-NEXT: i32 0, label %for.cond
; CHECK-NEXT: ]
; CHECK:loop.loopexit:
; CHECK-NEXT: unreachable
; CHECK:NonEmptyUnreachableBlock:
; CHECK-NEXT: call void @f()
; CHECK-NEXT: call void @g()
; CHECK-NEXT: unreachable
}
define void @test_unswitch_switch_with_nonempty_unreachable2() {
; CHECK-LABEL: @test_unswitch_switch_with_nonempty_unreachable2()
entry:
br label %loop
loop:
%cleanup.dest.slot.0 = select i1 undef, i32 5, i32 undef
br label %for.cond
for.cond:
switch i32 %cleanup.dest.slot.0, label %for.cond [
i32 0, label %for.cond
i32 1, label %NonEmptyUnreachableBlock
i32 2, label %loop.loopexit
]
loop.loopexit:
unreachable
NonEmptyUnreachableBlock:
call void @f()
call void @g()
unreachable
; CHECK:loop:
; CHECK-NEXT: %cleanup.dest.slot.0 = select i1 undef, i32 5, i32 undef
; CHECK-NEXT: switch i32 %cleanup.dest.slot.0, label %loop.split [
; CHECK-NEXT: i32 1, label %NonEmptyUnreachableBlock
; CHECK-NEXT: ]
; CHECK:loop.split:
; CHECK-NEXT: br label %for.cond
; CHECK:for.cond:
; CHECK-NEXT: switch i32 %cleanup.dest.slot.0, label %for.cond.backedge [
; CHECK-NEXT: i32 0, label %for.cond.backedge
; CHECK-NEXT: i32 2, label %loop.loopexit
; CHECK-NEXT: ]
; CHECK:for.cond.backedge:
; CHECK-NEXT: br label %for.cond
; CHECK:loop.loopexit:
@ -1292,3 +1345,34 @@ NonEmptyUnreachableBlock:
; CHECK-NEXT: call void @g()
; CHECK-NEXT: unreachable
}
; PR45355
define void @test_unswitch_switch_with_duplicate_edge() {
; CHECK-LABEL: @test_unswitch_switch_with_duplicate_edge()
entry:
br label %lbl1
lbl1: ; preds = %entry
%cleanup.dest.slot.0 = select i1 undef, i32 5, i32 undef
br label %for.cond1
for.cond1: ; preds = %for.cond1, %lbl1
switch i32 %cleanup.dest.slot.0, label %UnifiedUnreachableBlock [
i32 0, label %for.cond1
i32 5, label %UnifiedUnreachableBlock
i32 2, label %lbl1.loopexit
]
UnifiedUnreachableBlock: ; preds = %for.cond1, %for.cond1
unreachable
lbl1.loopexit: ; preds = %for.cond1
unreachable
; CHECK: for.cond1:
; CHECK-NEXT: switch i32 %cleanup.dest.slot.0, label %UnifiedUnreachableBlock [
; CHECK-NEXT: i32 0, label %for.cond1
; CHECK-NEXT: i32 5, label %UnifiedUnreachableBlock
; CHECK-NEXT: i32 2, label %lbl1.loopexit
; CHECK-NEXT: ]
}