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Add support for end_lifetime in DCE #38315

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Merged
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Jul 10, 2021
Merged

Add support for end_lifetime in DCE #38315

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10 changes: 6 additions & 4 deletions lib/SILOptimizer/Transforms/DeadCodeElimination.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -45,10 +45,11 @@ namespace {
// FIXME: Reconcile the similarities between this and
// isInstructionTriviallyDead.
static bool seemsUseful(SILInstruction *I) {
// Even though begin_access/destroy_value/copy_value have side-effects, they
// can be DCE'ed if they do not have useful dependencies/reverse dependencies
// Even though begin_access/destroy_value/copy_value/end_lifetime have
// side-effects, they can be DCE'ed if they do not have useful
// dependencies/reverse dependencies
if (isa<BeginAccessInst>(I) || isa<CopyValueInst>(I) ||
isa<DestroyValueInst>(I))
isa<DestroyValueInst>(I) || isa<EndLifetimeInst>(I))
return false;

// A load [copy] is okay to be DCE'ed if there are no useful dependencies
Expand Down Expand Up @@ -268,7 +269,8 @@ void DCE::markLive() {
break;
}
case SILInstructionKind::DestroyValueInst:
case SILInstructionKind::EndBorrowInst: {
case SILInstructionKind::EndBorrowInst:
case SILInstructionKind::EndLifetimeInst: {
// The instruction is live only if it's operand value is also live
addReverseDependency(I.getOperand(0), &I);
break;
Expand Down
41 changes: 41 additions & 0 deletions test/SILOptimizer/dead_code_elimination_nontrivial_ossa.sil
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Expand Up @@ -611,3 +611,44 @@ bb3:
return %9999 : $()
}

// CHECK-LABEL: sil [ossa] @dce_deadendlifetime1 :
// CHECK-NOT: end_lifetime
// CHECK-LABEL: } // end sil function 'dce_deadendlifetime1'
sil [ossa] @dce_deadendlifetime1 : $@convention(thin) () -> () {
bb0:
cond_br undef, bb1, bb2

bb1:
br bb3(undef : $Klass)

bb2:
br bb3(undef : $Klass)

bb3(%2 : @owned $Klass):
end_lifetime %2 : $Klass
%res = tuple ()
return %res : $()
}

// CHECK-LABEL: sil [ossa] @dce_deadendlifetime2 :
// CHECK-NOT: end_lifetime
// CHECK-LABEL: } // end sil function 'dce_deadendlifetime2'
sil [ossa] @dce_deadendlifetime2 : $@convention(thin) () -> () {
bb0:
cond_br undef, bb1, bb2

bb1:
br bb3(undef : $Klass)

bb2:
br bb3(undef : $Klass)

bb3(%2 : @owned $Klass):
br bb4(%2 : $Klass)

bb4(%3 : @owned $Klass):
end_lifetime %3 : $Klass
%res = tuple ()
return %res : $()
}