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a17dbc7c74
This change could impact Swift programs that previously appeared well-behaved, but weren't fully tested in debug mode. Now, when running in release mode, they may trap with the message "error: overlapping accesses...". Recent optimizations have brought performance where I think it needs to be for adoption. More optimizations are planned, and some benchmarks should be further improved, but at this point we're ready to begin receiving bug reports. That will help prioritize the remaining work for Swift 5. Of the 656 public microbenchmarks in the Swift repository, there are still several regressions larger than 10%: TEST OLD NEW DELTA RATIO ClassArrayGetter2 139 1307 +840.3% **0.11x** HashTest 631 1233 +95.4% **0.51x** NopDeinit 21269 32389 +52.3% **0.66x** Hanoi 1478 2166 +46.5% **0.68x** Calculator 127 158 +24.4% **0.80x** Dictionary3OfObjects 391 455 +16.4% **0.86x** CSVParsingAltIndices2 526 604 +14.8% **0.87x** Prims 549 626 +14.0% **0.88x** CSVParsingAlt2 1252 1411 +12.7% **0.89x** Dictionary4OfObjects 206 232 +12.6% **0.89x** ArrayInClass 46 51 +10.9% **0.90x** The common pattern in these benchmarks is to define an array of data as a class property and to repeatedly access that array through the class reference. Each of those class property accesses now incurs a runtime call. Naturally, introducing a runtime call in a loop that otherwise does almost no work incurs substantial overhead. This is similar to the issue caused by automatic reference counting. In some cases, more sophistacated optimization will be able to determine the same object is repeatedly accessed. Furthermore, the overhead of the runtime call itself can be improved. But regardless of how well we optimize, there will always a class of microbenchmarks in which the runtime check has a noticeable impact. As a general guideline, avoid performing class property access within the most performance critical loops, particularly on different objects in each loop iteration. If that isn't possible, it may help if the visibility of those class properties is private or internal.
230 lines
7.1 KiB
Swift
230 lines
7.1 KiB
Swift
// RUN: %target-swift-frontend -O -emit-sil -enforce-exclusivity=unchecked %s | %FileCheck %s
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// RUN: %target-swift-frontend -O -wmo -emit-sil -enforce-exclusivity=unchecked %s | %FileCheck -check-prefix=CHECK-WMO %s
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// Check that values of internal and private global variables, which are provably assigned only
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// once, are propagated into their uses and enable further optimizations like constant
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// propagation, simplifications, etc.
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// Define some global variables.
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public var VD = 3.1415
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public var VI = 100
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private var PVD = 3.1415
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private var PVI = 100
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private var PVIAssignTwice = 1
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private var PVITakenAddress = 1
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internal var IVD = 3.1415
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internal var IVI = 100
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internal var IVIAssignTwice = 1
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internal var IVITakenAddress = 1
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// Taking the address of a global should prevent from performing the propagation of its value.
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@inline(never)
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@_optimize(none)
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public func takeInout<T>(_ x: inout T) {
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}
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// Compiler should detect that we assign a global here as well and prevent a global optimization.
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public func assignSecondTime() {
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PVIAssignTwice = 2
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IVIAssignTwice = 2
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}
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// Having multiple assignments to a global should prevent from performing the propagation of its value.
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// Loads from private global variables can be removed,
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// because they cannot be changed outside of this source file.
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// CHECK-LABEL: sil [noinline] @$s28globalopt_global_propagation013test_private_B11_var_doubleSdyF
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// CHECK: bb0:
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// CHECK-NOT: global_addr
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// CHECK: float_literal
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// CHECK: struct
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// CHECK: return
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@inline(never)
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public func test_private_global_var_double() -> Double {
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return PVD + 1.0
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}
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// Loads from private global variables can be removed,
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// because they cannot be changed outside of this source file.
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// CHECK-LABEL: sil [noinline] @$s28globalopt_global_propagation013test_private_B8_var_intSiyF
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// CHECK: bb0:
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// CHECK-NOT: global_addr
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// CHECK: integer_literal
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// CHECK: struct
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// CHECK: return
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@inline(never)
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public func test_private_global_var_int() -> Int {
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return PVI + 1
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}
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// Loads from internal global variables can be removed if this is a WMO compilation, because
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// they cannot be changed outside of this module.
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// CHECK-WMO-LABEL: sil [noinline] @$s28globalopt_global_propagation014test_internal_B11_var_doubleSdyF
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// CHECK-WMO: bb0:
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// CHECK-WMO-NOT: global_addr
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// CHECK-WMO: float_literal
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// CHECK-WMO: struct
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// CHECK-WMO: return
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@inline(never)
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public func test_internal_global_var_double() -> Double {
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return IVD + 1.0
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}
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// Loads from internal global variables can be removed if this is a WMO compilation, because
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// they cannot be changed outside of this module.
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// CHECK-WMO-LABEL: sil [noinline] @$s28globalopt_global_propagation014test_internal_B8_var_intSiyF
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// CHECK_WMO: bb0:
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// CHECK-WMO-NOT: global_addr
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// CHECK-WMO: integer_literal
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// CHECK-WMO: struct
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// CHECK_WMO: return
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@inline(never)
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public func test_internal_global_var_int() -> Int {
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return IVI + 1
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}
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// Loads from public global variables cannot be removed, because their values could be changed elsewhere.
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// CHECK-WMO-LABEL: sil [noinline] @$s28globalopt_global_propagation012test_public_B11_var_doubleSdyF
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// CHECK-WMO: bb0:
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// CHECK-WMO-NEXT: global_addr
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// CHECK-WMO-NEXT: struct_element_addr
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// CHECK-WMO-NEXT: load
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@inline(never)
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public func test_public_global_var_double() -> Double {
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return VD + 1.0
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}
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// Loads from public global variables cannot be removed, because their values could be changed elsewhere.
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// CHECK-LABEL: sil [noinline] @$s28globalopt_global_propagation012test_public_B8_var_intSiyF
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// CHECK: bb0:
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// CHECK-NEXT: global_addr
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// CHECK-NEXT: struct_element_addr
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// CHECK-NEXT: load
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@inline(never)
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public func test_public_global_var_int() -> Int {
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return VI + 1
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}
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// Values of globals cannot be propagated as there are multiple assignments to it.
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// CHECK-WMO-LABEL: sil [noinline] @$s28globalopt_global_propagation026test_internal_and_private_B25_var_with_two_assignmentsSiyF
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// CHECK-WMO: bb0:
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// CHECK-WMO: global_addr
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// CHECK-WMO: global_addr
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// CHECK-WMO: struct_element_addr
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// CHECK-WMO: load
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// CHECK-WMO: struct_element_addr
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// CHECK-WMO: load
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// CHECK-WMO: return
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@inline(never)
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public func test_internal_and_private_global_var_with_two_assignments() -> Int {
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return IVIAssignTwice + PVIAssignTwice
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}
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// Values of globals cannot be propagated as their address was taken and
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// therefore their value could have been changed elsewhere.
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// CHECK-WMO-LABEL: sil @$s28globalopt_global_propagation05test_B13_take_addressSiyF
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// CHECK-WMO: bb0:
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// CHECK-WMO: global_addr
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// CHECK-WMO: global_addr
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// CHECK-WMO: struct_element_addr
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// CHECK-WMO: load
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// CHECK-WMO: struct_element_addr
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// CHECK-WMO: load
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// CHECK-WMO: return
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public func test_global_take_address() -> Int {
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takeInout(&PVITakenAddress)
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takeInout(&IVITakenAddress)
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return IVITakenAddress + PVITakenAddress
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}
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struct IntWrapper1 {
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let val: Int
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}
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struct IntWrapper2 {
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let val: IntWrapper1
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}
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struct IntWrapper3 {
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let val: IntWrapper2
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}
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struct IntWrapper4 {
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let val: IntWrapper2
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let val2: IntWrapper1
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}
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let IW3 = IntWrapper3(val: IntWrapper2(val: IntWrapper1(val: 10)))
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let IW4 = IntWrapper4(val: IntWrapper2(val: IntWrapper1(val: 10)), val2: IntWrapper1(val: 100))
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// Test accessing single Int wrapped into multiple structs, where each struct has only one field.
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// CHECK-LABEL: sil [noinline] @$s28globalopt_global_propagation34test_let_struct_wrapped_single_intSiyF
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// CHECK: bb0:
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// CHECK-NOT: global_addr
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// CHECK: integer_literal
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// CHECK: struct
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// CHECK: return
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// CHECK-WMO-LABEL: sil [noinline] @$s28globalopt_global_propagation34test_let_struct_wrapped_single_intSiyF
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// CHECK-WMO: bb0:
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// CHECK-WMO-NOT: global_addr
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// CHECK-WMO: integer_literal
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// CHECK-WMO: struct
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// CHECK-WMO: return
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@inline(never)
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public func test_let_struct_wrapped_single_int() -> Int {
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return IW3.val.val.val + 1
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}
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// Test accessing multiple Int fields wrapped into multiple structs, where each struct may have
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// multiple fields.
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// CHECK-LABEL: sil [noinline] @$s28globalopt_global_propagation37test_let_struct_wrapped_multiple_intsSiyF
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// CHECK: bb0:
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// CHECK-NOT: global_addr
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// CHECK: integer_literal
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// CHECK: struct
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// CHECK: return
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// CHECK-WMO-LABEL: sil [noinline] @$s28globalopt_global_propagation37test_let_struct_wrapped_multiple_intsSiyF
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// CHECK-WMO: bb0:
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// CHECK-WMO-NOT: global_addr
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// CHECK-WMO: integer_literal
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// CHECK-WMO: struct
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// CHECK-WMO: return
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@inline(never)
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public func test_let_struct_wrapped_multiple_ints() -> Int {
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return IW4.val.val.val + IW4.val2.val + 1
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}
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let IT1 = ((10, 20), 30, 40)
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let IT2 = (100, 200, 300)
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// Test accessing multiple Int fields wrapped into multiple tuples, where each tuple may have
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// multiple fields.
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// CHECK-LABEL: sil [noinline] @$s28globalopt_global_propagation27test_let_tuple_wrapped_intsSiyF
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// CHECK: bb0:
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// CHECK-NOT: global_addr
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// CHECK: integer_literal
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// CHECK: struct
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// CHECK: return
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// CHECK-WMO-LABEL: sil [noinline] @$s28globalopt_global_propagation27test_let_tuple_wrapped_intsSiyF
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// CHECK-WMO: bb0:
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// CHECK-WMO-NOT: global_addr
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// CHECK-WMO: integer_literal
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// CHECK-WMO: struct
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// CHECK-WMO: return
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@inline(never)
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public func test_let_tuple_wrapped_ints() -> Int {
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return IT1.0.0 + IT2.1
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}
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