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Merge pull request swiftlang#34280 from gottesmm/pr-94bbbe81fdf8a4d1212dd582f8fad1c619207575
When converting load [copy] -> load_borrow, do not insert end_borrow if the block insert point is a dead end block.
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‎lib/SILOptimizer/SemanticARC/OwnershipLiveRange.cpp‎

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Original file line numberDiff line numberDiff line change
@@ -13,6 +13,8 @@
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#include "OwnershipLiveRange.h"
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#include "OwnershipPhiOperand.h"
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#include "swift/SIL/BasicBlockUtils.h"
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using namespace swift;
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using namespace swift::semanticarc;
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@@ -162,6 +164,61 @@ void OwnershipLiveRange::insertEndBorrowsAtDestroys(
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auto loc = RegularLocation::getAutoGeneratedLocation();
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while (!scratch.empty()) {
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auto *insertPoint = scratch.pop_back_val();
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// Do not insert end_borrow if the block insert point is a dead end block.
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//
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// DISCUSSION: This is important to do since otherwise, we may be implicitly
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// reducing the lifetime of a value which we can not do yet since we do not
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// require all interior pointer instructions to be guarded by borrows
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// (yet). Once that constraint is in place, we will not have this problem.
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//
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// Consider a situation where one has a @owned switch_enum on an
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// indirect box case which is post-dominated by an unreachable that we want
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// to convert to @guaranteed:
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//
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// enum MyEnum {
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// indirect case FirstCase(Int)
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// ...
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// }
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//
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// bb0(%in_guaranteed_addr : $*MyEnum):
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// ...
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// %0 = load [copy] %in_guaranteed_addr : $*MyEnum
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// switch_enum %0 : $MyEnum, case #MyEnum.FirstCase: bb1, ...
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//
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// bb1(%1 : @owned ${ var Int }):
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// %2 = project_box %1 : ${ var Int }, 0
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// %3 = load [trivial] %2 : $*Int
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// apply %log(%3) : $@convention(thin) (Int) -> ()
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// unreachable
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//
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// In this case, we will not have a destroy_value on the box, but we may
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// have a project_box on the box. This is ok since we are going to leak the
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// value. But since we are using all consuming uses to determine the
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// lifetime, we will want to insert an end_borrow at the head of the
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// switch_enum dest block like follows:
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//
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// bb0(%in_guaranteed_addr : $*MyEnum):
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// ...
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// %0 = load_borrow %in_guaranteed_addr : $*MyEnum
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// switch_enum %0 : $MyEnum, case #MyEnum.FirstCase: bb1, ...
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//
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// bb1(%1 : @guaranteed ${ var Int }):
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// end_borrow %1 : ${ var Int }
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// %2 = project_box %1 : ${ var Int }, 0
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// %3 = load [trivial] %2 : $*Int
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// apply %log(%3) : $@convention(thin) (Int) -> ()
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// unreachable
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//
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// which would violate ownership invariants. Instead, we need to realize
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// that %1 is dominated by a dead end block so we may not have a
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// destroy_value upon it meaning we should just not insert the end_borrow
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// here. If we have a destroy_value upon it (since we did not get rid of a
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// destroy_value), then we will still get rid of the destroy_value if we are
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// going to optimize this, so we are still correct.
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if (deadEndBlocks.isDeadEnd(insertPoint->getParent()))
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continue;
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SILBuilderWithScope builder(insertPoint);
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builder.createEndBorrow(loc, newGuaranteedValue);
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}

‎test/SILOptimizer/semantic-arc-opts.sil‎

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Original file line numberDiff line numberDiff line change
@@ -79,6 +79,16 @@ class SubclassLet: ClassLet {}
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sil_global [let] @a_let_global : $Klass
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sil_global @a_var_global : $Klass
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enum EnumWithIndirectCase {
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case first
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indirect case second(Builtin.NativeObject)
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}
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struct StructWithEnumWithIndirectCaseField {
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var i: Builtin.Int23
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var field : EnumWithIndirectCase
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}
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///////////
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// Tests //
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///////////
@@ -2727,3 +2737,72 @@ bbEnd:
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return %9999 : $()
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}
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// CHECK-LABEL: sil [ossa] @enum_with_indirect_case_projectbox_copyvalue_deadend : $@convention(thin) (@guaranteed StructWithEnumWithIndirectCaseField) -> () {
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// CHECK-NOT: copy_value
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// CHECK: } // end sil function 'enum_with_indirect_case_projectbox_copyvalue_deadend'
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sil [ossa] @enum_with_indirect_case_projectbox_copyvalue_deadend : $@convention(thin) (@guaranteed StructWithEnumWithIndirectCaseField) -> () {
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bb0(%0 : @guaranteed $StructWithEnumWithIndirectCaseField):
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%1 = struct_extract %0 : $StructWithEnumWithIndirectCaseField, #StructWithEnumWithIndirectCaseField.field
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%1a = copy_value %1 : $EnumWithIndirectCase
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switch_enum %1a : $EnumWithIndirectCase, case #EnumWithIndirectCase.first!enumelt: bb1, case #EnumWithIndirectCase.second!enumelt: bb2
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bb1:
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%9999 = tuple()
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return %9999 : $()
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// NOTE: Eventually this will need to be changed when project_box has to be
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// guarded by begin_borrow.
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bb2(%2 : @owned ${ var Builtin.NativeObject }):
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%3 = project_box %2 : ${ var Builtin.NativeObject }, 0
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%4 = load [copy] %3 : $*Builtin.NativeObject
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%user = function_ref @guaranteed_user : $@convention(thin) (@guaranteed Builtin.NativeObject) -> ()
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apply %user(%4) : $@convention(thin) (@guaranteed Builtin.NativeObject) -> ()
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unreachable
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}
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// CHECK-LABEL: sil [ossa] @enum_with_indirect_case_projectbox_loadcopy_to_loadborrow_deadend : $@convention(thin) (@in_guaranteed EnumWithIndirectCase) -> () {
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// CHECK: bb0
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// CHECK-NEXT: load_borrow
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// CHECK: } // end sil function 'enum_with_indirect_case_projectbox_loadcopy_to_loadborrow_deadend'
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sil [ossa] @enum_with_indirect_case_projectbox_loadcopy_to_loadborrow_deadend : $@convention(thin) (@in_guaranteed EnumWithIndirectCase) -> () {
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bb0(%0 : $*EnumWithIndirectCase):
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%1 = load [copy] %0 : $*EnumWithIndirectCase
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switch_enum %1 : $EnumWithIndirectCase, case #EnumWithIndirectCase.first!enumelt: bb1, case #EnumWithIndirectCase.second!enumelt: bb2
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bb1:
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%9999 = tuple()
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return %9999 : $()
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// NOTE: Eventually this will need to be changed when project_box has to be
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// guarded by begin_borrow.
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bb2(%2 : @owned ${ var Builtin.NativeObject }):
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%3 = project_box %2 : ${ var Builtin.NativeObject }, 0
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%4 = load [copy] %3 : $*Builtin.NativeObject
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%user = function_ref @guaranteed_user : $@convention(thin) (@guaranteed Builtin.NativeObject) -> ()
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apply %user(%4) : $@convention(thin) (@guaranteed Builtin.NativeObject) -> ()
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unreachable
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}
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// CHECK-LABEL: sil [ossa] @enum_with_indirect_case_projectbox_loadcopy_to_loadborrow_deadend_2 : $@convention(thin) (@in_guaranteed EnumWithIndirectCase) -> () {
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// CHECK: bb0
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// CHECK-NEXT: load_borrow
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// CHECK: } // end sil function 'enum_with_indirect_case_projectbox_loadcopy_to_loadborrow_deadend_2'
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sil [ossa] @enum_with_indirect_case_projectbox_loadcopy_to_loadborrow_deadend_2 : $@convention(thin) (@in_guaranteed EnumWithIndirectCase) -> () {
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bb0(%0 : $*EnumWithIndirectCase):
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%1 = load [copy] %0 : $*EnumWithIndirectCase
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switch_enum %1 : $EnumWithIndirectCase, case #EnumWithIndirectCase.first!enumelt: bb1, case #EnumWithIndirectCase.second!enumelt: bb2
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bb1:
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%9999 = tuple()
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return %9999 : $()
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// NOTE: Eventually this will need to be changed when project_box has to be
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// guarded by begin_borrow.
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bb2(%2 : @owned ${ var Builtin.NativeObject }):
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%3 = project_box %2 : ${ var Builtin.NativeObject }, 0
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%4 = load [copy] %3 : $*Builtin.NativeObject
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%user = function_ref @guaranteed_user : $@convention(thin) (@guaranteed Builtin.NativeObject) -> ()
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apply %user(%4) : $@convention(thin) (@guaranteed Builtin.NativeObject) -> ()
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destroy_value %2 : ${ var Builtin.NativeObject }
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unreachable
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}

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