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[DFAJumpThreading] Don't bail early after encountering unpredictable values #119774

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Merged
merged 1 commit into from
Dec 25, 2024
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[DFAJumpThreading] Don't bail early after encountering unpredictable values #119774

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29 changes: 12 additions & 17 deletions llvm/lib/Transforms/Scalar/DFAJumpThreading.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -109,7 +109,7 @@ static cl::opt<unsigned> MaxNumVisitiedPaths(
"dfa-max-num-visited-paths",
cl::desc(
"Max number of blocks visited while enumerating paths around a switch"),
cl::Hidden, cl::init(2000));
cl::Hidden, cl::init(2500));

static cl::opt<unsigned>
MaxNumPaths("dfa-max-num-paths",
Expand Down Expand Up @@ -754,17 +754,15 @@ struct AllSwitchPaths {
return Res;
}

/// Walk the use-def chain and collect all the state-defining instructions.
///
/// Return an empty map if unpredictable values encountered inside the basic
/// blocks of \p LoopPaths.
/// Walk the use-def chain and collect all the state-defining blocks and the
/// PHI nodes in those blocks that define the state.
StateDefMap getStateDefMap() const {
StateDefMap Res;
Value *FirstDef = Switch->getOperand(0);
assert(isa<PHINode>(FirstDef) && "The first definition must be a phi.");
PHINode *FirstDef = dyn_cast<PHINode>(Switch->getOperand(0));
assert(FirstDef && "The first definition must be a phi.");

SmallVector<PHINode *, 8> Stack;
Stack.push_back(dyn_cast<PHINode>(FirstDef));
Stack.push_back(FirstDef);
SmallSet<Value *, 16> SeenValues;

while (!Stack.empty()) {
Expand All @@ -774,18 +772,15 @@ struct AllSwitchPaths {
SeenValues.insert(CurPhi);

for (BasicBlock *IncomingBB : CurPhi->blocks()) {
Value *Incoming = CurPhi->getIncomingValueForBlock(IncomingBB);
PHINode *IncomingPhi =
dyn_cast<PHINode>(CurPhi->getIncomingValueForBlock(IncomingBB));
if (!IncomingPhi)
continue;
bool IsOutsideLoops = !SwitchOuterLoop->contains(IncomingBB);
if (Incoming == FirstDef || isa<ConstantInt>(Incoming) ||
SeenValues.contains(Incoming) || IsOutsideLoops) {
if (SeenValues.contains(IncomingPhi) || IsOutsideLoops)
continue;
}

// Any unpredictable value inside the loops means we must bail out.
if (!isa<PHINode>(Incoming))
return StateDefMap();

Stack.push_back(cast<PHINode>(Incoming));
Stack.push_back(IncomingPhi);
}
}

Expand Down
42 changes: 37 additions & 5 deletions llvm/test/Transforms/DFAJumpThreading/dfa-unfold-select.ll
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Expand Up @@ -381,26 +381,58 @@ define void @pr65222(i32 %flags, i1 %cmp, i1 %tobool.not) {
; CHECK: then:
; CHECK-NEXT: br i1 [[TOBOOL_NOT:%.*]], label [[COND1_SI_UNFOLD_TRUE:%.*]], label [[COND_SI_UNFOLD_TRUE:%.*]]
; CHECK: cond.si.unfold.true:
; CHECK-NEXT: br i1 [[CMP]], label [[TOUNFOLD_SI_UNFOLD_FALSE1:%.*]], label [[COND_SI_UNFOLD_FALSE_JT0:%.*]]
; CHECK: cond.si.unfold.true.jt2:
; CHECK-NEXT: [[DOTSI_UNFOLD_PHI:%.*]] = phi i32 [ 2, [[THEN]] ]
; CHECK-NEXT: br i1 [[CMP]], label [[TOUNFOLD_SI_UNFOLD_FALSE:%.*]], label [[COND_SI_UNFOLD_FALSE:%.*]]
; CHECK: cond.si.unfold.false:
; CHECK-NEXT: [[DOTSI_UNFOLD_PHI1:%.*]] = phi i32 [ 0, [[COND_SI_UNFOLD_TRUE]] ]
; CHECK-NEXT: br label [[TOUNFOLD_SI_UNFOLD_FALSE]]
; CHECK-NEXT: br label [[TOUNFOLD_SI_UNFOLD_FALSE1]]
; CHECK: cond.si.unfold.false.jt0:
; CHECK-NEXT: [[DOTSI_UNFOLD_PHI1_JT0:%.*]] = phi i32 [ 0, [[COND_SI_UNFOLD_TRUE1:%.*]] ]
; CHECK-NEXT: br label [[TOUNFOLD_SI_UNFOLD_FALSE_JT0:%.*]]
; CHECK: tounfold.si.unfold.false:
; CHECK-NEXT: [[COND_SI_UNFOLD_PHI:%.*]] = phi i32 [ [[DOTSI_UNFOLD_PHI]], [[COND_SI_UNFOLD_TRUE]] ], [ [[DOTSI_UNFOLD_PHI1]], [[COND_SI_UNFOLD_FALSE]] ]
; CHECK-NEXT: [[COND_SI_UNFOLD_PHI:%.*]] = phi i32 [ poison, [[COND_SI_UNFOLD_TRUE1]] ], [ [[DOTSI_UNFOLD_PHI1]], [[COND_SI_UNFOLD_FALSE]] ]
; CHECK-NEXT: br label [[IF_END]]
; CHECK: tounfold.si.unfold.false.jt0:
; CHECK-NEXT: [[COND_SI_UNFOLD_PHI_JT0:%.*]] = phi i32 [ [[DOTSI_UNFOLD_PHI1_JT0]], [[COND_SI_UNFOLD_FALSE_JT0]] ]
; CHECK-NEXT: br label [[IF_END_JT0:%.*]]
; CHECK: tounfold.si.unfold.false.jt2:
; CHECK-NEXT: [[COND_SI_UNFOLD_PHI_JT2:%.*]] = phi i32 [ [[DOTSI_UNFOLD_PHI]], [[COND_SI_UNFOLD_TRUE]] ]
; CHECK-NEXT: br label [[IF_END_JT2:%.*]]
; CHECK: cond1.si.unfold.true:
; CHECK-NEXT: br i1 [[CMP]], label [[IF_END]], label [[COND1_SI_UNFOLD_FALSE_JT1:%.*]]
; CHECK: cond1.si.unfold.true.jt3:
; CHECK-NEXT: [[DOTSI_UNFOLD_PHI2:%.*]] = phi i32 [ 3, [[THEN]] ]
; CHECK-NEXT: br i1 [[CMP]], label [[IF_END]], label [[COND1_SI_UNFOLD_FALSE:%.*]]
; CHECK-NEXT: br i1 [[CMP]], label [[IF_END_JT3:%.*]], label [[COND1_SI_UNFOLD_FALSE:%.*]]
; CHECK: cond1.si.unfold.false:
; CHECK-NEXT: [[DOTSI_UNFOLD_PHI3:%.*]] = phi i32 [ 1, [[COND1_SI_UNFOLD_TRUE]] ]
; CHECK-NEXT: br label [[IF_END]]
; CHECK: cond1.si.unfold.false.jt1:
; CHECK-NEXT: [[DOTSI_UNFOLD_PHI3_JT1:%.*]] = phi i32 [ 1, [[COND1_SI_UNFOLD_TRUE1:%.*]] ]
; CHECK-NEXT: br label [[IF_END_JT1:%.*]]
; CHECK: if.end:
; CHECK-NEXT: [[UNFOLDED:%.*]] = phi i32 [ [[FLAGS:%.*]], [[WHILE_COND]] ], [ [[COND_SI_UNFOLD_PHI]], [[TOUNFOLD_SI_UNFOLD_FALSE]] ], [ [[DOTSI_UNFOLD_PHI2]], [[COND1_SI_UNFOLD_TRUE]] ], [ [[DOTSI_UNFOLD_PHI3]], [[COND1_SI_UNFOLD_FALSE]] ]
; CHECK-NEXT: [[OTHER:%.*]] = phi i32 [ [[FLAGS]], [[WHILE_COND]] ], [ 0, [[TOUNFOLD_SI_UNFOLD_FALSE]] ], [ 0, [[COND1_SI_UNFOLD_TRUE]] ], [ 0, [[COND1_SI_UNFOLD_FALSE]] ]
; CHECK-NEXT: [[UNFOLDED:%.*]] = phi i32 [ [[FLAGS:%.*]], [[WHILE_COND]] ], [ [[COND_SI_UNFOLD_PHI]], [[TOUNFOLD_SI_UNFOLD_FALSE1]] ], [ poison, [[COND1_SI_UNFOLD_TRUE1]] ], [ [[DOTSI_UNFOLD_PHI3]], [[COND1_SI_UNFOLD_FALSE]] ]
; CHECK-NEXT: [[OTHER:%.*]] = phi i32 [ [[FLAGS]], [[WHILE_COND]] ], [ 0, [[TOUNFOLD_SI_UNFOLD_FALSE1]] ], [ 0, [[COND1_SI_UNFOLD_TRUE1]] ], [ 0, [[COND1_SI_UNFOLD_FALSE]] ]
; CHECK-NEXT: switch i32 [[UNFOLDED]], label [[UNREACHABLE:%.*]] [
; CHECK-NEXT: i32 0, label [[SW_BB:%.*]]
; CHECK-NEXT: ]
; CHECK: if.end.jt1:
; CHECK-NEXT: [[UNFOLDED_JT1:%.*]] = phi i32 [ [[DOTSI_UNFOLD_PHI3_JT1]], [[COND1_SI_UNFOLD_FALSE_JT1]] ]
; CHECK-NEXT: [[OTHER_JT1:%.*]] = phi i32 [ 0, [[COND1_SI_UNFOLD_FALSE_JT1]] ]
; CHECK-NEXT: br label [[UNREACHABLE]]
; CHECK: if.end.jt3:
; CHECK-NEXT: [[UNFOLDED_JT3:%.*]] = phi i32 [ [[DOTSI_UNFOLD_PHI2]], [[COND1_SI_UNFOLD_TRUE]] ]
; CHECK-NEXT: [[OTHER_JT3:%.*]] = phi i32 [ 0, [[COND1_SI_UNFOLD_TRUE]] ]
; CHECK-NEXT: br label [[UNREACHABLE]]
; CHECK: if.end.jt0:
; CHECK-NEXT: [[UNFOLDED_JT0:%.*]] = phi i32 [ [[COND_SI_UNFOLD_PHI_JT0]], [[TOUNFOLD_SI_UNFOLD_FALSE_JT0]] ]
; CHECK-NEXT: [[OTHER_JT0:%.*]] = phi i32 [ 0, [[TOUNFOLD_SI_UNFOLD_FALSE_JT0]] ]
; CHECK-NEXT: br label [[SW_BB]]
; CHECK: if.end.jt2:
; CHECK-NEXT: [[UNFOLDED_JT2:%.*]] = phi i32 [ [[COND_SI_UNFOLD_PHI_JT2]], [[TOUNFOLD_SI_UNFOLD_FALSE]] ]
; CHECK-NEXT: [[OTHER_JT2:%.*]] = phi i32 [ 0, [[TOUNFOLD_SI_UNFOLD_FALSE]] ]
; CHECK-NEXT: br label [[UNREACHABLE]]
; CHECK: unreachable:
; CHECK-NEXT: unreachable
; CHECK: sw.bb:
Expand Down
40 changes: 38 additions & 2 deletions llvm/test/Transforms/DFAJumpThreading/negative.ll
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Expand Up @@ -218,9 +218,45 @@ for.end:
declare i32 @arbitrary_function()

; Don't confuse %state.2 for the initial switch value.
; [ 3, %case2 ] can still be threaded.
define i32 @negative6(i32 %init) {
; REMARK: SwitchNotPredictable
; REMARK-NEXT: negative6
; CHECK-LABEL: define i32 @negative6(
; CHECK-SAME: i32 [[INIT:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[INIT]], 0
; CHECK-NEXT: br label %[[LOOP_2:.*]]
; CHECK: [[LOOP_2]]:
; CHECK-NEXT: [[STATE_2:%.*]] = call i32 @arbitrary_function()
; CHECK-NEXT: br label %[[LOOP_3:.*]]
; CHECK: [[LOOP_3]]:
; CHECK-NEXT: [[STATE:%.*]] = phi i32 [ [[STATE_2]], %[[LOOP_2]] ]
; CHECK-NEXT: switch i32 [[STATE]], label %[[INFLOOP_I:.*]] [
; CHECK-NEXT: i32 2, label %[[CASE2:.*]]
; CHECK-NEXT: i32 3, label %[[CASE3:.*]]
; CHECK-NEXT: i32 4, label %[[CASE4:.*]]
; CHECK-NEXT: i32 0, label %[[CASE0:.*]]
; CHECK-NEXT: i32 1, label %[[CASE1:.*]]
; CHECK-NEXT: ]
; CHECK: [[LOOP_3_JT3:.*]]:
; CHECK-NEXT: [[STATE_JT3:%.*]] = phi i32 [ 3, %[[CASE2]] ]
; CHECK-NEXT: br label %[[CASE3]]
; CHECK: [[CASE2]]:
; CHECK-NEXT: br label %[[LOOP_3_JT3]]
; CHECK: [[CASE3]]:
; CHECK-NEXT: br i1 [[CMP]], label %[[LOOP_2_BACKEDGE:.*]], label %[[CASE4]]
; CHECK: [[CASE4]]:
; CHECK-NEXT: br label %[[LOOP_2_BACKEDGE]]
; CHECK: [[LOOP_2_BACKEDGE]]:
; CHECK-NEXT: br label %[[LOOP_2]]
; CHECK: [[CASE0]]:
; CHECK-NEXT: br label %[[EXIT:.*]]
; CHECK: [[CASE1]]:
; CHECK-NEXT: br label %[[EXIT]]
; CHECK: [[INFLOOP_I]]:
; CHECK-NEXT: br label %[[INFLOOP_I]]
; CHECK: [[EXIT]]:
; CHECK-NEXT: ret i32 0
;
entry:
%cmp = icmp eq i32 %init, 0
br label %loop.2
Expand Down
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