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[DCE] Tweaked code to end borrows before destroys. #39760

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Merged
merged 1 commit into from
Oct 19, 2021
Merged

[DCE] Tweaked code to end borrows before destroys. #39760

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8 changes: 7 additions & 1 deletion lib/SILOptimizer/Transforms/DeadCodeElimination.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -601,13 +601,19 @@ bool DCE::removeDead() {
// may also have been dead and a destroy_value of its baseValue may
// have been inserted before the pred's terminator. Make sure to
// adjust the insertPt before any destroy_value.
//
// FIXME: This code currently can reorder destroys, e.g., when the
// block already contains a destroy_value just before the
// terminator. Fix this by making note of the added
// destroy_value insts and only moving the insertion point
// before those that are newly added.
for (SILInstruction &predInst : llvm::reverse(*pred)) {
if (&predInst == predTerm)
continue;
if (!isa<DestroyValueInst>(&predInst)) {
insertPt = &*std::next(predInst.getIterator());
break;
}
insertPt = &predInst;
}
}

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41 changes: 41 additions & 0 deletions test/SILOptimizer/dead_code_elimination_nontrivial_ossa.sil
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Expand Up @@ -679,3 +679,44 @@ exit:
%retval = tuple ()
return %retval : $()
}

// CHECK-LABEL: sil hidden [ossa] @add_end_borrow_after_destroy_value : {{.*}} {
// CHECK: bb0({{%[^,]+}} : $Builtin.Int1, [[INSTANCE_1:%[^,]+]] : @owned $Klass, {{%[^,]+}} : @owned $Klass):
// CHECK: [[LIFETIME_1:%[^,]+]] = begin_borrow [[INSTANCE_1]]
// CHECK: copy_value [[LIFETIME_1]]
// CHECK: cond_br {{%[^,]+}}, [[BASIC_BLOCK1:bb[0-9]+]], [[BASIC_BLOCK2:bb[0-9]+]]
// CHECK: [[BASIC_BLOCK1]]:
// CHECK: end_borrow [[LIFETIME_1]]
// CHECK: destroy_value [[INSTANCE_1]]
// CHECK: [[BASIC_BLOCK2]]:
// CHECK: end_borrow [[LIFETIME_1]]
// CHECK: destroy_value [[INSTANCE_1]]
// CHECK-LABEL: } // end sil function 'add_end_borrow_after_destroy_value'
sil hidden [ossa] @add_end_borrow_after_destroy_value : $@convention(thin) (Builtin.Int1, @owned Klass, @owned Klass) -> () {
bb0(%condition : $Builtin.Int1, %instance_1 : @owned $Klass, %instance_2 : @owned $Klass):
%lifetime_1 = begin_borrow %instance_1 : $Klass

%copy_1 = copy_value %lifetime_1 : $Klass
%stack_addr = alloc_stack $Klass
store %copy_1 to [init] %stack_addr : $*Klass
destroy_addr %stack_addr : $*Klass
dealloc_stack %stack_addr : $*Klass

cond_br %condition, bb1, bb2

bb1:
end_borrow %lifetime_1 : $Klass
destroy_value %instance_1 : $Klass
%lifetime_2 = begin_borrow %instance_2 : $Klass
br bb3(%instance_2 : $Klass, %lifetime_2 : $Klass)

bb2:
destroy_value %instance_2 : $Klass
br bb3(%instance_1 : $Klass, %lifetime_1 : $Klass)

bb3(%original : @owned $Klass, %lifetime : @guaranteed $Klass):
end_borrow %lifetime : $Klass
destroy_value %original : $Klass
%result = tuple ()
return %result : $()
}