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ConditionForwarding: don't violate ownership #79878

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Merged
merged 1 commit into from
Mar 11, 2025
Merged

ConditionForwarding: don't violate ownership #79878

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24 changes: 19 additions & 5 deletions lib/SILOptimizer/Transforms/ConditionForwarding.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -126,8 +126,25 @@ class ConditionForwarding : public SILFunctionTransform {

/// Returns true if all instructions of block \p BB are safe to be moved
/// across other code.
static bool hasNoRelevantSideEffects(SILBasicBlock *BB) {
static bool hasNoRelevantSideEffects(SILBasicBlock *BB, EnumInst *enumInst) {
for (SILInstruction &I : *BB) {
if (BB->getParent()->hasOwnership() && &I != enumInst) {
// The instruction must not use any (non-trivial) value because we don't
// do liveness analysis. When moving the block, there is no guarantee that
// the operand value is still alive at the new location.
for (Operand *op : I.getRealOperands()) {
SILValue opv = op->get();
// The `enum` is an exception, because it's a forwarded value and we already
// check that it's forwarded to the `switch_enum` at the new location.
if (opv == enumInst)
continue;
// If the value is defined in the block it's a block-local liferange.
if (opv->getParentBlock() == BB)
continue;
if (opv->getOwnershipKind() != OwnershipKind::None)
return false;
}
}
if (I.getMemoryBehavior() == MemoryBehavior::None)
continue;
if (auto *CF = dyn_cast<CondFailInst>(&I)) {
Expand All @@ -144,9 +161,6 @@ static bool hasNoRelevantSideEffects(SILBasicBlock *BB) {
return false;
continue;
}
if (isa<BeginBorrowInst>(&I) || isa<EndBorrowInst>(&I)) {
continue;
}
LLVM_DEBUG(llvm::dbgs() << "Bailing out, found inst with side-effects ");
LLVM_DEBUG(I.dump());
return false;
Expand Down Expand Up @@ -212,7 +226,7 @@ bool ConditionForwarding::tryOptimize(SwitchEnumInst *SEI) {
CommonBranchBlock = PredPred;

// We cannot move the block across other code if it has side-effects.
if (!hasNoRelevantSideEffects(Pred))
if (!hasNoRelevantSideEffects(Pred, EI))
return false;
PredBlocks.push_back(Pred);
}
Expand Down
35 changes: 35 additions & 0 deletions test/SILOptimizer/conditionforwarding_ossa.sil
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Original file line number Diff line number Diff line change
Expand Up @@ -419,3 +419,38 @@ bb6:
%15 = tuple ()
return %15
}

// CHECK-LABEL: sil [ossa] @copy_from_limited_liferange :
// CHECK: switch_enum
// CHECK-LABEL: } // end sil function 'copy_from_limited_liferange'
sil [ossa] @copy_from_limited_liferange : $@convention(thin) (Builtin.Int1, @guaranteed C) -> () {
bb0(%0 : $Builtin.Int1, %1 : @guaranteed $C):
%2 = begin_borrow [lexical] %1
cond_br %0, bb1, bb2

bb1:
%4 = copy_value %2
%5 = enum $Optional<C>, #Optional.some!enumelt, %4
br bb3(%5)

bb2:
%7 = enum $Optional<C>, #Optional.none!enumelt
br bb3(%7)

bb3(%9 : @owned $Optional<C>):
end_borrow %2
switch_enum %9, case #Optional.some!enumelt: bb5, case #Optional.none!enumelt: bb4

bb4:
br bb6

bb5(%13 : @owned $C):
destroy_value %13
br bb6

bb6:
%16 = tuple ()
return %16
}