[AutoDiff] Fix forward-mode differentiation ownership verification failure.

[dan-zheng]

Previously, LinearMapInfo::shouldDifferentiateInstruction had a special case
for copy_value, returning true for copy_value instructions with an active
operand.

This is unexpected and led to "leaked owned value" ownership verification
failures due to unnecessarily cloned copy_value instructions during
differential generation.

Now, the special case is removed, fixing the failures.
shouldDifferentiateInstruction returns true for copy_value instructions
whose operand and result are both active.

Resolves SR-13530.

---

Example:

import DifferentiationUnittest

// Note: `NonresilientTracked` is a non-trivial, non-resilient type.
@differentiable
func foo(_ x: NonresilientTracked<Float>) -> NonresilientTracked<Float> {
  precondition(x.value >= 0)
  return x
}

Before: ownership verification failure.

$ swiftc -Xfrontend -enable-experimental-forward-mode-differentiation -Xllvm -debug-only=differentiation error.swift

...

[AD] Activity info for foo at (parameters=(0) results=(0))
bb0:
[ACTIVE] %0 = argument of bb0 : $NonresilientTracked<Float> // users: %23, %3, %1
[NONE]   // function_ref implicit closure #1 in foo(_:)
  %2 = function_ref @$s5error3fooy23DifferentiationUnittest19NonresilientTrackedVySfGAFFSbyXEfu_ : $@convention(thin) (@guaranteed NonresilientTracked<Float>) -> Bool // user: %4
[VARIED]   %3 = copy_value %0 : $NonresilientTracked<Float> // user: %4
[VARIED]   %4 = partial_apply [callee_guaranteed] %2(%3) : $@convention(thin) (@guaranteed NonresilientTracked<Float>) -> Bool // users: %22, %5
[VARIED]   %5 = convert_escape_to_noescape [not_guaranteed] %4 : $@callee_guaranteed () -> Bool to $@noescape @callee_guaranteed () -> Bool // user: %20
[NONE]   %6 = string_literal utf8 "error/error.swift"    // user: %11
[NONE]   %7 = integer_literal $Builtin.Word, 17          // user: %11
[NONE]   %8 = integer_literal $Builtin.Int1, -1          // user: %11
[NONE]   %9 = metatype $@thin StaticString.Type          // user: %11
[NONE]   // function_ref StaticString.init(_builtinStringLiteral:utf8CodeUnitCount:isASCII:)
  %10 = function_ref @$ss12StaticStringV08_builtinB7Literal17utf8CodeUnitCount7isASCIIABBp_BwBi1_tcfC : $@convention(method) (Builtin.RawPointer, Builtin.Word, Builtin.Int1, @thin StaticString.Type) -> StaticString // user: %11
[NONE]   %11 = apply %10(%6, %7, %8, %9) : $@convention(method) (Builtin.RawPointer, Builtin.Word, Builtin.Int1, @thin StaticString.Type) -> StaticString // user: %20
[NONE]   %12 = integer_literal $Builtin.IntLiteral, 6    // user: %15
[NONE]   %13 = metatype $@thin UInt.Type                 // user: %15
[NONE]   // function_ref UInt.init(_builtinIntegerLiteral:)
  %14 = function_ref @$sSu22_builtinIntegerLiteralSuBI_tcfC : $@convention(method) (Builtin.IntLiteral, @thin UInt.Type) -> UInt // user: %15
[NONE]   %15 = apply %14(%12, %13) : $@convention(method) (Builtin.IntLiteral, @thin UInt.Type) -> UInt // user: %20
[NONE]   // function_ref default argument 1 of precondition(_:_:file:line:)
  %16 = function_ref @$ss12precondition__4file4lineySbyXK_SSyXKs12StaticStringVSutFfA0_ : $@convention(thin) () -> @owned @callee_guaranteed () -> @owned String // user: %17
[NONE]   %17 = apply %16() : $@convention(thin) () -> @owned @callee_guaranteed () -> @owned String // users: %21, %18
[NONE]   %18 = convert_escape_to_noescape [not_guaranteed] %17 : $@callee_guaranteed () -> @owned String to $@noescape @callee_guaranteed () -> @owned String // user: %20
[NONE]   // function_ref precondition(_:_:file:line:)
  %19 = function_ref @$ss12precondition__4file4lineySbyXK_SSyXKs12StaticStringVSutF : $@convention(thin) (@noescape @callee_guaranteed () -> Bool, @noescape @callee_guaranteed () -> @owned String, StaticString, UInt) -> () // user: %20
[NONE]   %20 = apply %19(%5, %18, %11, %15) : $@convention(thin) (@noescape @callee_guaranteed () -> Bool, @noescape @callee_guaranteed () -> @owned String, StaticString, UInt) -> ()
[ACTIVE]   %23 = copy_value %0 : $NonresilientTracked<Float> // user: %24

...

[AD] Original bb0: To differentiate or not to differentiate?
[ ]   debug_value %0 : $NonresilientTracked<Float>, let, name "x", argno 1 // id: %1
[ ]   // function_ref implicit closure #1 in foo(_:)
  %2 = function_ref @$s5error3fooy23DifferentiationUnittest19NonresilientTrackedVySfGAFFSbyXEfu_ : $@convention(thin) (@guaranteed NonresilientTracked<Float>) -> Bool // user: %4
[x]   %3 = copy_value %0 : $NonresilientTracked<Float> // user: %4
[ ]   %4 = partial_apply [callee_guaranteed] %2(%3) : $@convention(thin) (@guaranteed NonresilientTracked<Float>) -> Bool // users: %22, %5
[ ]   %5 = convert_escape_to_noescape [not_guaranteed] %4 : $@callee_guaranteed () -> Bool to $@noescape @callee_guaranteed () -> Bool // user: %20
[ ]   %6 = string_literal utf8 "error/error.swift"    // user: %11
[ ]   %7 = integer_literal $Builtin.Word, 17          // user: %11
[ ]   %8 = integer_literal $Builtin.Int1, -1          // user: %11
[ ]   %9 = metatype $@thin StaticString.Type          // user: %11
[ ]   // function_ref StaticString.init(_builtinStringLiteral:utf8CodeUnitCount:isASCII:)
  %10 = function_ref @$ss12StaticStringV08_builtinB7Literal17utf8CodeUnitCount7isASCIIABBp_BwBi1_tcfC : $@convention(method) (Builtin.RawPointer, Builtin.Word, Builtin.Int1, @thin StaticString.Type) -> StaticString // user: %11
[ ]   %11 = apply %10(%6, %7, %8, %9) : $@convention(method) (Builtin.RawPointer, Builtin.Word, Builtin.Int1, @thin StaticString.Type) -> StaticString // user: %20
[ ]   %12 = integer_literal $Builtin.IntLiteral, 6    // user: %15
[ ]   %13 = metatype $@thin UInt.Type                 // user: %15
[ ]   // function_ref UInt.init(_builtinIntegerLiteral:)
  %14 = function_ref @$sSu22_builtinIntegerLiteralSuBI_tcfC : $@convention(method) (Builtin.IntLiteral, @thin UInt.Type) -> UInt // user: %15
[ ]   %15 = apply %14(%12, %13) : $@convention(method) (Builtin.IntLiteral, @thin UInt.Type) -> UInt // user: %20
[ ]   // function_ref default argument 1 of precondition(_:_:file:line:)
  %16 = function_ref @$ss12precondition__4file4lineySbyXK_SSyXKs12StaticStringVSutFfA0_ : $@convention(thin) () -> @owned @callee_guaranteed () -> @owned String // user: %17
[ ]   %17 = apply %16() : $@convention(thin) () -> @owned @callee_guaranteed () -> @owned String // users: %21, %18
[ ]   %18 = convert_escape_to_noescape [not_guaranteed] %17 : $@callee_guaranteed () -> @owned String to $@noescape @callee_guaranteed () -> @owned String // user: %20
[ ]   // function_ref precondition(_:_:file:line:)
  %19 = function_ref @$ss12precondition__4file4lineySbyXK_SSyXKs12StaticStringVSutF : $@convention(thin) (@noescape @callee_guaranteed () -> Bool, @noescape @callee_guaranteed () -> @owned String, StaticString, UInt) -> () // user: %20
[ ]   %20 = apply %19(%5, %18, %11, %15) : $@convention(thin) (@noescape @callee_guaranteed () -> Bool, @noescape @callee_guaranteed () -> @owned String, StaticString, UInt) -> ()
[ ]   destroy_value %17 : $@callee_guaranteed () -> @owned String // id: %21
[ ]   destroy_value %4 : $@callee_guaranteed () -> Bool // id: %22
[x]   %23 = copy_value %0 : $NonresilientTracked<Float> // user: %24
[ ]   return %23 : $NonresilientTracked<Float>        // id: %24

...

[AD] Generated differential for foo:
// AD__foo__differential_src_0_wrt_0
sil hidden [ossa] @AD__foo__differential_src_0_wrt_0 : $@convention(thin) (@guaranteed NonresilientTracked<Float>, @owned _AD__foo_bb0__DF__src_0_wrt_0) -> @owned NonresilientTracked<Float> {
// %0                                             // users: %4, %3
// %1                                             // user: %2
bb0(%0 : @guaranteed $NonresilientTracked<Float>, %1 : $_AD__foo_bb0__DF__src_0_wrt_0):
  destructure_struct %1 : $_AD__foo_bb0__DF__src_0_wrt_0 // id: %2
  %3 = copy_value %0 : $NonresilientTracked<Float>
  %4 = copy_value %0 : $NonresilientTracked<Float> // user: %5
  return %4 : $NonresilientTracked<Float>         // id: %5
} // end sil function 'AD__foo__differential_src_0_wrt_0'

...

Begin Error in Function: 'AD__foo__differential_src_0_wrt_0'
Error! Found a leaked owned value that was never consumed.
Value:   %3 = copy_value %0 : $NonresilientTracked<Float>

End Error in Function: 'AD__foo__differential_src_0_wrt_0'
Found ownership error?!
triggering standard assertion failure routine

After: no error.

[dan-zheng]

Note: I tried to track down the origin of this code. I found it was added by this commit, though it existed in a different form prior to the commit.

I think this special-case for copy_value was just an oversight/latent error.

[dan-zheng]

@swift-ci Please smoke test

[dan-zheng]

The Windows CI failure seems unrelated. Merging now.