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SimplifyDestructure: support simplifying a destructure_struct with a copy_value in place
Replace ``` %s = struct (%0, %1, %2) %c = copy_value %s // can also be a chain of multiple copies (%3, %4, %5) = destructure_struct %c ``` with ``` %c0 = copy_value %0 %c1 = copy_value %1 %c2 = copy_value %2 %s = struct (%0, %1, %2) // keep the original struct ``` and replace the results %3, %4, %5 with %c0, %c1, %c2, respectively.
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‎SwiftCompilerSources/Sources/Optimizer/InstructionSimplification/SimplifyDestructure.swift

Lines changed: 48 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -31,15 +31,55 @@ extension DestructureTupleInst : OnoneSimplifyable {
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extension DestructureStructInst : OnoneSimplifyable {
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func simplify(_ context: SimplifyContext) {
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// Eliminate the redundant instruction pair
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// ```
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// %s = struct (%0, %1, %2)
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// (%3, %4, %5) = destructure_struct %s
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// ```
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// and replace the results %3, %4, %5 with %0, %1, %2, respectively
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//
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if let str = self.struct as? StructInst {
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switch self.struct {
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case let str as StructInst:
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// Eliminate the redundant instruction pair
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// ```
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// %s = struct (%0, %1, %2)
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// (%3, %4, %5) = destructure_struct %s
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// ```
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// and replace the results %3, %4, %5 with %0, %1, %2, respectively
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//
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tryReplaceConstructDestructPair(construct: str, destruct: self, context)
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case let copy as CopyValueInst:
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// Similar to the pattern above, but with a copy_value:
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// Replace
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// ```
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// %s = struct (%0, %1, %2)
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// %c = copy_value %s // can also be a chain of multiple copies
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// (%3, %4, %5) = destructure_struct %c
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// ```
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// with
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// ```
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// %c0 = copy_value %0
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// %c1 = copy_value %1
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// %c2 = copy_value %2
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// %s = struct (%0, %1, %2) // keep the original struct
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// ```
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// and replace the results %3, %4, %5 with %c0, %c1, %c2, respectively.
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//
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// This transformation has the advantage that we can do it even if the `struct` instruction
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// has other uses than the `copy_value`.
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//
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if copy.uses.singleUse?.instruction == self,
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let structInst = copy.fromValue.lookThroughCopy as? StructInst,
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structInst.parentBlock == self.parentBlock
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{
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for (result, operand) in zip(self.results, structInst.operands) {
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if operand.value.type.isTrivial(in: parentFunction) {
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result.uses.replaceAll(with: operand.value, context)
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} else {
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let builder = Builder(before: structInst, context)
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let copiedOperand = builder.createCopyValue(operand: operand.value)
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result.uses.replaceAll(with: copiedOperand, context)
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}
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}
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context.erase(instruction: self)
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context.erase(instruction: copy)
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}
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default:
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break
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}
4484
}
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}

‎test/SILOptimizer/simplify_destructure_struct.sil

Lines changed: 70 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -70,4 +70,74 @@ bb0(%0 : @owned $String, %1 : $Int):
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return %4 : $String
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}
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// CHECK-LABEL: sil [ossa] @forward_with_copy :
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// CHECK: %2 = copy_value %0
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// CHECK: %3 = struct $S (%0 : $String, %1 : $Int)
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// CHECK: fix_lifetime %1
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// CHECK: destroy_value %3
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// CHECK: return %2
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// CHECK: } // end sil function 'forward_with_copy'
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sil [ossa] @forward_with_copy : $@convention(thin) (@owned String, Int) -> @owned String {
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bb0(%0 : @owned $String, %1 : $Int):
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%2 = struct $S (%0 : $String, %1 : $Int)
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%3 = copy_value %2 : $S
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(%4, %5) = destructure_struct %3 : $S
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fix_lifetime %5 : $Int
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destroy_value %2 : $S
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return %4 : $String
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}
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// CHECK-LABEL: sil [ossa] @forward_with_two_copies :
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// CHECK: %2 = copy_value %0
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// CHECK: %3 = struct $S (%0 : $String, %1 : $Int)
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// CHECK: %4 = copy_value %3
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// CHECK: fix_lifetime %1
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// CHECK: destroy_value %3
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// CHECK: destroy_value %4
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// CHECK: return %2
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// CHECK: } // end sil function 'forward_with_two_copies'
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sil [ossa] @forward_with_two_copies : $@convention(thin) (@owned String, Int) -> @owned String {
100+
bb0(%0 : @owned $String, %1 : $Int):
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%2 = struct $S (%0 : $String, %1 : $Int)
102+
%3 = copy_value %2 : $S
103+
%4 = copy_value %3 : $S
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(%5, %6) = destructure_struct %4 : $S
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fix_lifetime %6 : $Int
106+
destroy_value %2 : $S
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destroy_value %3 : $S
108+
return %5 : $String
109+
}
110+
111+
// CHECK-LABEL: sil [ossa] @copy_has_other_uses :
112+
// CHECK: destructure_struct
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// CHECK: } // end sil function 'copy_has_other_uses'
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sil [ossa] @copy_has_other_uses : $@convention(thin) (@owned String, Int) -> @owned String {
115+
bb0(%0 : @owned $String, %1 : $Int):
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%2 = struct $S (%0 : $String, %1 : $Int)
117+
%3 = copy_value %2 : $S
118+
fix_lifetime %3 : $S
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(%5, %6) = destructure_struct %3 : $S
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fix_lifetime %6 : $Int
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destroy_value %2 : $S
122+
return %5 : $String
123+
}
124+
125+
// CHECK-LABEL: sil [ossa] @different_basic_block :
126+
// CHECK: bb2:
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// CHECK: destructure_struct
128+
// CHECK: } // end sil function 'different_basic_block'
129+
sil [ossa] @different_basic_block : $@convention(thin) (@owned String, Int) -> @owned String {
130+
bb0(%0 : @owned $String, %1 : $Int):
131+
%2 = struct $S (%0 : $String, %1 : $Int)
132+
%3 = copy_value %2 : $S
133+
cond_br undef, bb1, bb2
134+
bb1:
135+
destroy_value %3 : $S
136+
unreachable
137+
bb2:
138+
(%4, %5) = destructure_struct %3 : $S
139+
fix_lifetime %5 : $Int
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destroy_value %2 : $S
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return %4 : $String
142+
}
73143

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