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// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package ssa
// tightenTupleSelectors ensures that tuple selectors (Select0, Select1,
// and SelectN ops) are in the same block as their tuple generator. The
// function also ensures that there are no duplicate tuple selectors.
// These properties are expected by the scheduler but may not have
// been maintained by the optimization pipeline up to this point.
//
// See issues 16741 and 39472.
func tightenTupleSelectors(f *Func) {
selectors := make(map[struct {
id ID
which int
}]*Value)
for _, b := range f.Blocks {
for _, selector := range b.Values {
// Key fields for de-duplication
var tuple *Value
idx := 0
switch selector.Op {
default:
continue
case OpSelect1:
idx = 1
fallthrough
case OpSelect0:
tuple = selector.Args[0]
if !tuple.Type.IsTuple() {
f.Fatalf("arg of tuple selector %s is not a tuple: %s", selector.String(), tuple.LongString())
}
case OpSelectN:
tuple = selector.Args[0]
idx = int(selector.AuxInt)
if !tuple.Type.IsResults() {
f.Fatalf("arg of result selector %s is not a results: %s", selector.String(), tuple.LongString())
}
}
// If there is a pre-existing selector in the target block then
// use that. Do this even if the selector is already in the
// target block to avoid duplicate tuple selectors.
key := struct {
id ID
which int
}{tuple.ID, idx}
if t := selectors[key]; t != nil {
if selector != t {
selector.copyOf(t)
}
continue
}
// If the selector is in the wrong block copy it into the target
// block.
if selector.Block != tuple.Block {
t := selector.copyInto(tuple.Block)
selector.copyOf(t)
selectors[key] = t
continue
}
// The selector is in the target block. Add it to the map so it
// cannot be duplicated.
selectors[key] = selector
}
}
}
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