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[InstCombine] Allow freezing multiple out-of-loop values #155638

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[InstCombine] Allow freezing multiple out-of-loop values #155638

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30 changes: 14 additions & 16 deletions llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5032,32 +5032,28 @@ Instruction *InstCombinerImpl::foldFreezeIntoRecurrence(FreezeInst &FI,
// backedge values (possibly dropping poison flags along the way) until we
// reach the phi again. In that case, we can move the freeze to the start
// value.
Use *StartU = nullptr;
SmallVector<Use *> StartUses;
SmallVector<Value *> Worklist;
for (Use &U : PN->incoming_values()) {
if (DT.dominates(PN->getParent(), PN->getIncomingBlock(U))) {
BasicBlock *StartBB = PN->getIncomingBlock(U);
Value *StartV = U.get();
if (DT.dominates(PN->getParent(), StartBB)) {
// Add backedge value to worklist.
Worklist.push_back(U.get());
Worklist.push_back(StartV);
continue;
}

// Don't bother handling multiple start values.
if (StartU)
bool StartNeedsFreeze = !isGuaranteedNotToBeUndefOrPoison(StartV);
// We can't insert freeze if a start value is the result of the
// terminator (e.g. an invoke).
if (StartNeedsFreeze && StartBB->getTerminator() == StartV)
return nullptr;
StartU = &U;
StartUses.push_back(&U);
}

if (!StartU || Worklist.empty())
if (StartUses.empty() || Worklist.empty())
return nullptr; // Not a recurrence.

Value *StartV = StartU->get();
BasicBlock *StartBB = PN->getIncomingBlock(*StartU);
bool StartNeedsFreeze = !isGuaranteedNotToBeUndefOrPoison(StartV);
// We can't insert freeze if the start value is the result of the
// terminator (e.g. an invoke).
if (StartNeedsFreeze && StartBB->getTerminator() == StartV)
return nullptr;

SmallPtrSet<Value *, 32> Visited;
SmallVector<Instruction *> DropFlags;
while (!Worklist.empty()) {
Expand All @@ -5084,7 +5080,9 @@ Instruction *InstCombinerImpl::foldFreezeIntoRecurrence(FreezeInst &FI,
for (Instruction *I : DropFlags)
I->dropPoisonGeneratingAnnotations();

if (StartNeedsFreeze) {
for (Use *StartU : StartUses) {
Value *StartV = StartU->get();
BasicBlock *StartBB = PN->getIncomingBlock(*StartU);
Builder.SetInsertPoint(StartBB->getTerminator());
Value *FrozenStartV = Builder.CreateFreeze(StartV,
StartV->getName() + ".fr");
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7 changes: 4 additions & 3 deletions llvm/test/Transforms/InstCombine/freeze.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -1106,13 +1106,14 @@ define void @fold_phi_multiple_start_values(i1 %c, i32 %init, i32 %init2, i32 %n
; CHECK-LABEL: define void @fold_phi_multiple_start_values(
; CHECK-SAME: i1 [[C:%.*]], i32 [[INIT:%.*]], i32 [[INIT2:%.*]], i32 [[N:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*]]:
; CHECK-NEXT: [[INIT_FR:%.*]] = freeze i32 [[INIT]]
; CHECK-NEXT: br i1 [[C]], label %[[IF:.*]], label %[[LOOP:.*]]
; CHECK: [[IF]]:
; CHECK-NEXT: [[INIT2_FR:%.*]] = freeze i32 [[INIT2]]
; CHECK-NEXT: br label %[[LOOP]]
; CHECK: [[LOOP]]:
; CHECK-NEXT: [[I:%.*]] = phi i32 [ [[INIT]], %[[ENTRY]] ], [ [[INIT2]], %[[IF]] ], [ [[I_NEXT:%.*]], %[[LOOP]] ]
; CHECK-NEXT: [[I_FR:%.*]] = freeze i32 [[I]]
; CHECK-NEXT: [[I_NEXT]] = add nuw nsw i32 [[I_FR]], 1
; CHECK-NEXT: [[I:%.*]] = phi i32 [ [[INIT_FR]], %[[ENTRY]] ], [ [[INIT2_FR]], %[[IF]] ], [ [[I_NEXT:%.*]], %[[LOOP]] ]
; CHECK-NEXT: [[I_NEXT]] = add i32 [[I]], 1
; CHECK-NEXT: [[COND:%.*]] = icmp eq i32 [[I_NEXT]], [[N]]
; CHECK-NEXT: br i1 [[COND]], label %[[LOOP]], label %[[EXIT:.*]]
; CHECK: [[EXIT]]:
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