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[CVP] Check whether the default case is reachable (#79993)
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This patch eliminates unreachable default cases using context-sensitive
range information.
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@dtcxzyw
dtcxzyw authored Jan 31, 2024
1 parent 8e77390 commit a034e65
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Showing 3 changed files with 341 additions and 5 deletions.
34 changes: 34 additions & 0 deletions llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -371,6 +371,7 @@ static bool processSwitch(SwitchInst *I, LazyValueInfo *LVI,
{ // Scope for SwitchInstProfUpdateWrapper. It must not live during
// ConstantFoldTerminator() as the underlying SwitchInst can be changed.
SwitchInstProfUpdateWrapper SI(*I);
unsigned ReachableCaseCount = 0;

for (auto CI = SI->case_begin(), CE = SI->case_end(); CI != CE;) {
ConstantInt *Case = CI->getCaseValue();
Expand Down Expand Up @@ -407,6 +408,33 @@ static bool processSwitch(SwitchInst *I, LazyValueInfo *LVI,

// Increment the case iterator since we didn't delete it.
++CI;
++ReachableCaseCount;
}

BasicBlock *DefaultDest = SI->getDefaultDest();
if (ReachableCaseCount > 1 &&
!isa<UnreachableInst>(DefaultDest->getFirstNonPHIOrDbg())) {
ConstantRange CR = LVI->getConstantRangeAtUse(I->getOperandUse(0),
/*UndefAllowed*/ false);
// The default dest is unreachable if all cases are covered.
if (!CR.isSizeLargerThan(ReachableCaseCount)) {
BasicBlock *NewUnreachableBB =
BasicBlock::Create(BB->getContext(), "default.unreachable",
BB->getParent(), DefaultDest);
new UnreachableInst(BB->getContext(), NewUnreachableBB);

DefaultDest->removePredecessor(BB);
SI->setDefaultDest(NewUnreachableBB);

if (SuccessorsCount[DefaultDest] == 1)
DTU.applyUpdatesPermissive(
{{DominatorTree::Delete, BB, DefaultDest}});
DTU.applyUpdatesPermissive(
{{DominatorTree::Insert, BB, NewUnreachableBB}});

++NumDeadCases;
Changed = true;
}
}
}

Expand Down Expand Up @@ -1227,6 +1255,12 @@ CorrelatedValuePropagationPass::run(Function &F, FunctionAnalysisManager &AM) {
if (!Changed) {
PA = PreservedAnalyses::all();
} else {
#if defined(EXPENSIVE_CHECKS)
assert(DT->verify(DominatorTree::VerificationLevel::Full));
#else
assert(DT->verify(DominatorTree::VerificationLevel::Fast));
#endif // EXPENSIVE_CHECKS

PA.preserve<DominatorTreeAnalysis>();
PA.preserve<LazyValueAnalysis>();
}
Expand Down
11 changes: 6 additions & 5 deletions llvm/test/Transforms/CorrelatedValuePropagation/basic.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -442,7 +442,7 @@ define i32 @switch_range(i32 %cond) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[S:%.*]] = urem i32 [[COND:%.*]], 3
; CHECK-NEXT: [[S1:%.*]] = add nuw nsw i32 [[S]], 1
; CHECK-NEXT: switch i32 [[S1]], label [[UNREACHABLE:%.*]] [
; CHECK-NEXT: switch i32 [[S1]], label [[DEFAULT_UNREACHABLE:%.*]] [
; CHECK-NEXT: i32 1, label [[EXIT1:%.*]]
; CHECK-NEXT: i32 2, label [[EXIT2:%.*]]
; CHECK-NEXT: i32 3, label [[EXIT1]]
Expand All @@ -451,6 +451,8 @@ define i32 @switch_range(i32 %cond) {
; CHECK-NEXT: ret i32 1
; CHECK: exit2:
; CHECK-NEXT: ret i32 2
; CHECK: default.unreachable:
; CHECK-NEXT: unreachable
; CHECK: unreachable:
; CHECK-NEXT: ret i32 0
;
Expand Down Expand Up @@ -513,10 +515,9 @@ define i8 @switch_defaultdest_multipleuse(i8 %t0) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[O:%.*]] = or i8 [[T0:%.*]], 1
; CHECK-NEXT: [[R:%.*]] = srem i8 1, [[O]]
; CHECK-NEXT: switch i8 [[R]], label [[EXIT:%.*]] [
; CHECK-NEXT: i8 0, label [[EXIT]]
; CHECK-NEXT: i8 1, label [[EXIT]]
; CHECK-NEXT: ]
; CHECK-NEXT: br label [[EXIT:%.*]]
; CHECK: default.unreachable:
; CHECK-NEXT: unreachable
; CHECK: exit:
; CHECK-NEXT: ret i8 0
;
Expand Down
301 changes: 301 additions & 0 deletions llvm/test/Transforms/CorrelatedValuePropagation/switch.ll
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Original file line number Diff line number Diff line change
@@ -0,0 +1,301 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
; RUN: opt < %s -passes=correlated-propagation -S | FileCheck %s

define i32 @test_unreachable_default(i32 noundef %num) {
; CHECK-LABEL: define i32 @test_unreachable_default(
; CHECK-SAME: i32 noundef [[NUM:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[SUB:%.*]] = add i32 [[NUM]], -120
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[SUB]], 3
; CHECK-NEXT: [[COND:%.*]] = select i1 [[CMP]], i32 [[SUB]], i32 2
; CHECK-NEXT: switch i32 [[COND]], label [[DEFAULT_UNREACHABLE:%.*]] [
; CHECK-NEXT: i32 0, label [[SW_BB:%.*]]
; CHECK-NEXT: i32 1, label [[SW_BB2:%.*]]
; CHECK-NEXT: i32 2, label [[SW_BB4:%.*]]
; CHECK-NEXT: ]
; CHECK: sw.bb:
; CHECK-NEXT: [[CALL:%.*]] = call i32 @call0()
; CHECK-NEXT: br label [[CLEANUP:%.*]]
; CHECK: sw.bb2:
; CHECK-NEXT: [[CALL3:%.*]] = call i32 @call1()
; CHECK-NEXT: br label [[CLEANUP]]
; CHECK: sw.bb4:
; CHECK-NEXT: [[CALL5:%.*]] = call i32 @call2()
; CHECK-NEXT: br label [[CLEANUP]]
; CHECK: default.unreachable:
; CHECK-NEXT: unreachable
; CHECK: sw.default:
; CHECK-NEXT: [[CALL6:%.*]] = call i32 @call3()
; CHECK-NEXT: br label [[CLEANUP]]
; CHECK: cleanup:
; CHECK-NEXT: [[RETVAL_0:%.*]] = phi i32 [ [[CALL6]], [[SW_DEFAULT:%.*]] ], [ [[CALL5]], [[SW_BB4]] ], [ [[CALL3]], [[SW_BB2]] ], [ [[CALL]], [[SW_BB]] ]
; CHECK-NEXT: ret i32 [[RETVAL_0]]
;
entry:
%sub = add i32 %num, -120
%cmp = icmp ult i32 %sub, 3
%cond = select i1 %cmp, i32 %sub, i32 2
switch i32 %cond, label %sw.default [
i32 0, label %sw.bb
i32 1, label %sw.bb2
i32 2, label %sw.bb4
]

sw.bb:
%call = call i32 @call0()
br label %cleanup

sw.bb2:
%call3 = call i32 @call1()
br label %cleanup

sw.bb4:
%call5 = call i32 @call2()
br label %cleanup

sw.default:
%call6 = call i32 @call3()
br label %cleanup

cleanup:
%retval.0 = phi i32 [ %call6, %sw.default ], [ %call5, %sw.bb4 ], [ %call3, %sw.bb2 ], [ %call, %sw.bb ]
ret i32 %retval.0
}

define i32 @test_unreachable_default_shared_edge(i32 noundef %num) {
; CHECK-LABEL: define i32 @test_unreachable_default_shared_edge(
; CHECK-SAME: i32 noundef [[NUM:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[SUB:%.*]] = add i32 [[NUM]], -120
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[SUB]], 3
; CHECK-NEXT: [[COND:%.*]] = select i1 [[CMP]], i32 [[SUB]], i32 2
; CHECK-NEXT: switch i32 [[COND]], label [[DEFAULT_UNREACHABLE:%.*]] [
; CHECK-NEXT: i32 0, label [[SW_BB:%.*]]
; CHECK-NEXT: i32 1, label [[SW_BB2:%.*]]
; CHECK-NEXT: i32 2, label [[SW_BB4:%.*]]
; CHECK-NEXT: ]
; CHECK: sw.bb:
; CHECK-NEXT: [[CALL:%.*]] = call i32 @call0()
; CHECK-NEXT: br label [[CLEANUP:%.*]]
; CHECK: sw.bb2:
; CHECK-NEXT: [[CALL3:%.*]] = call i32 @call1()
; CHECK-NEXT: br label [[CLEANUP]]
; CHECK: default.unreachable:
; CHECK-NEXT: unreachable
; CHECK: sw.bb4:
; CHECK-NEXT: [[CALL5:%.*]] = call i32 @call4(i32 [[SUB]])
; CHECK-NEXT: br label [[CLEANUP]]
; CHECK: cleanup:
; CHECK-NEXT: [[RETVAL_0:%.*]] = phi i32 [ [[CALL5]], [[SW_BB4]] ], [ [[CALL3]], [[SW_BB2]] ], [ [[CALL]], [[SW_BB]] ]
; CHECK-NEXT: ret i32 [[RETVAL_0]]
;
entry:
%sub = add i32 %num, -120
%cmp = icmp ult i32 %sub, 3
%cond = select i1 %cmp, i32 %sub, i32 2
switch i32 %cond, label %sw.bb4 [
i32 0, label %sw.bb
i32 1, label %sw.bb2
i32 2, label %sw.bb4
]

sw.bb:
%call = call i32 @call0()
br label %cleanup

sw.bb2:
%call3 = call i32 @call1()
br label %cleanup

sw.bb4:
%val = phi i32 [ %sub, %entry ], [ %sub, %entry ]
%call5 = call i32 @call4(i32 %val)
br label %cleanup

cleanup:
%retval.0 = phi i32 [ %call5, %sw.bb4 ], [ %call3, %sw.bb2 ], [ %call, %sw.bb ]
ret i32 %retval.0
}

; Negative tests

define i32 @test_reachable_default(i32 noundef %num) {
; CHECK-LABEL: define i32 @test_reachable_default(
; CHECK-SAME: i32 noundef [[NUM:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[SUB:%.*]] = add i32 [[NUM]], -120
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[SUB]], 3
; CHECK-NEXT: [[COND:%.*]] = select i1 [[CMP]], i32 [[SUB]], i32 4
; CHECK-NEXT: switch i32 [[COND]], label [[SW_DEFAULT:%.*]] [
; CHECK-NEXT: i32 0, label [[SW_BB:%.*]]
; CHECK-NEXT: i32 1, label [[SW_BB2:%.*]]
; CHECK-NEXT: i32 2, label [[SW_BB4:%.*]]
; CHECK-NEXT: ]
; CHECK: sw.bb:
; CHECK-NEXT: [[CALL:%.*]] = call i32 @call0()
; CHECK-NEXT: br label [[CLEANUP:%.*]]
; CHECK: sw.bb2:
; CHECK-NEXT: [[CALL3:%.*]] = call i32 @call1()
; CHECK-NEXT: br label [[CLEANUP]]
; CHECK: sw.bb4:
; CHECK-NEXT: [[CALL5:%.*]] = call i32 @call2()
; CHECK-NEXT: br label [[CLEANUP]]
; CHECK: sw.default:
; CHECK-NEXT: [[CALL6:%.*]] = call i32 @call3()
; CHECK-NEXT: br label [[CLEANUP]]
; CHECK: cleanup:
; CHECK-NEXT: [[RETVAL_0:%.*]] = phi i32 [ [[CALL6]], [[SW_DEFAULT]] ], [ [[CALL5]], [[SW_BB4]] ], [ [[CALL3]], [[SW_BB2]] ], [ [[CALL]], [[SW_BB]] ]
; CHECK-NEXT: ret i32 [[RETVAL_0]]
;
entry:
%sub = add i32 %num, -120
%cmp = icmp ult i32 %sub, 3
%cond = select i1 %cmp, i32 %sub, i32 4
switch i32 %cond, label %sw.default [
i32 0, label %sw.bb
i32 1, label %sw.bb2
i32 2, label %sw.bb4
]

sw.bb:
%call = call i32 @call0()
br label %cleanup

sw.bb2:
%call3 = call i32 @call1()
br label %cleanup

sw.bb4:
%call5 = call i32 @call2()
br label %cleanup

sw.default:
%call6 = call i32 @call3()
br label %cleanup

cleanup:
%retval.0 = phi i32 [ %call6, %sw.default ], [ %call5, %sw.bb4 ], [ %call3, %sw.bb2 ], [ %call, %sw.bb ]
ret i32 %retval.0
}

define i32 @test_unreachable_default_cond_may_be_undef(i32 %num) {
; CHECK-LABEL: define i32 @test_unreachable_default_cond_may_be_undef(
; CHECK-SAME: i32 [[NUM:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[SUB:%.*]] = add i32 [[NUM]], -120
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[SUB]], 3
; CHECK-NEXT: [[COND:%.*]] = select i1 [[CMP]], i32 [[SUB]], i32 2
; CHECK-NEXT: switch i32 [[COND]], label [[SW_DEFAULT:%.*]] [
; CHECK-NEXT: i32 0, label [[SW_BB:%.*]]
; CHECK-NEXT: i32 1, label [[SW_BB2:%.*]]
; CHECK-NEXT: i32 2, label [[SW_BB4:%.*]]
; CHECK-NEXT: ]
; CHECK: sw.bb:
; CHECK-NEXT: [[CALL:%.*]] = call i32 @call0()
; CHECK-NEXT: br label [[CLEANUP:%.*]]
; CHECK: sw.bb2:
; CHECK-NEXT: [[CALL3:%.*]] = call i32 @call1()
; CHECK-NEXT: br label [[CLEANUP]]
; CHECK: sw.bb4:
; CHECK-NEXT: [[CALL5:%.*]] = call i32 @call2()
; CHECK-NEXT: br label [[CLEANUP]]
; CHECK: sw.default:
; CHECK-NEXT: [[CALL6:%.*]] = call i32 @call3()
; CHECK-NEXT: br label [[CLEANUP]]
; CHECK: cleanup:
; CHECK-NEXT: [[RETVAL_0:%.*]] = phi i32 [ [[CALL6]], [[SW_DEFAULT]] ], [ [[CALL5]], [[SW_BB4]] ], [ [[CALL3]], [[SW_BB2]] ], [ [[CALL]], [[SW_BB]] ]
; CHECK-NEXT: ret i32 [[RETVAL_0]]
;
entry:
%sub = add i32 %num, -120
%cmp = icmp ult i32 %sub, 3
%cond = select i1 %cmp, i32 %sub, i32 2
switch i32 %cond, label %sw.default [
i32 0, label %sw.bb
i32 1, label %sw.bb2
i32 2, label %sw.bb4
]

sw.bb:
%call = call i32 @call0()
br label %cleanup

sw.bb2:
%call3 = call i32 @call1()
br label %cleanup

sw.bb4:
%call5 = call i32 @call2()
br label %cleanup

sw.default:
%call6 = call i32 @call3()
br label %cleanup

cleanup:
%retval.0 = phi i32 [ %call6, %sw.default ], [ %call5, %sw.bb4 ], [ %call3, %sw.bb2 ], [ %call, %sw.bb ]
ret i32 %retval.0
}

define i32 @test_default_is_already_unreachable(i32 %num) {
; CHECK-LABEL: define i32 @test_default_is_already_unreachable(
; CHECK-SAME: i32 [[NUM:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[SUB:%.*]] = add i32 [[NUM]], -120
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[SUB]], 3
; CHECK-NEXT: [[COND:%.*]] = select i1 [[CMP]], i32 [[SUB]], i32 2
; CHECK-NEXT: switch i32 [[COND]], label [[SW_DEFAULT:%.*]] [
; CHECK-NEXT: i32 0, label [[SW_BB:%.*]]
; CHECK-NEXT: i32 1, label [[SW_BB2:%.*]]
; CHECK-NEXT: i32 2, label [[SW_BB4:%.*]]
; CHECK-NEXT: ]
; CHECK: sw.bb:
; CHECK-NEXT: [[CALL:%.*]] = call i32 @call0()
; CHECK-NEXT: br label [[CLEANUP:%.*]]
; CHECK: sw.bb2:
; CHECK-NEXT: [[CALL3:%.*]] = call i32 @call1()
; CHECK-NEXT: br label [[CLEANUP]]
; CHECK: sw.bb4:
; CHECK-NEXT: [[CALL5:%.*]] = call i32 @call2()
; CHECK-NEXT: br label [[CLEANUP]]
; CHECK: sw.default:
; CHECK-NEXT: unreachable
; CHECK: cleanup:
; CHECK-NEXT: [[RETVAL_0:%.*]] = phi i32 [ [[CALL5]], [[SW_BB4]] ], [ [[CALL3]], [[SW_BB2]] ], [ [[CALL]], [[SW_BB]] ]
; CHECK-NEXT: ret i32 [[RETVAL_0]]
;
entry:
%sub = add i32 %num, -120
%cmp = icmp ult i32 %sub, 3
%cond = select i1 %cmp, i32 %sub, i32 2
switch i32 %cond, label %sw.default [
i32 0, label %sw.bb
i32 1, label %sw.bb2
i32 2, label %sw.bb4
]

sw.bb:
%call = call i32 @call0()
br label %cleanup

sw.bb2:
%call3 = call i32 @call1()
br label %cleanup

sw.bb4:
%call5 = call i32 @call2()
br label %cleanup

sw.default:
unreachable

cleanup:
%retval.0 = phi i32 [ %call5, %sw.bb4 ], [ %call3, %sw.bb2 ], [ %call, %sw.bb ]
ret i32 %retval.0
}

declare i32 @call0()
declare i32 @call1()
declare i32 @call2()
declare i32 @call3()
declare i32 @call4(i32)

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