tuple.go

     1  // Copyright 2020 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package ssacompile
     6  
     7  import (
     8  	"cmd/compile/internal/ssa"
     9  	"cmd/compile/internal/ssa/ssaop"
    10  )
    11  
    12  // tightenTupleSelectors ensures that tuple selectors (Select0, Select1,
    13  // and SelectN ops) are in the same block as their tuple generator. The
    14  // function also ensures that there are no duplicate tuple selectors.
    15  // These properties are expected by the scheduler but may not have
    16  // been maintained by the optimization pipeline up to this point.
    17  //
    18  // See issues 16741 and 39472.
    19  func tightenTupleSelectors(f *ssa.Func) {
    20  	selectors := make(map[struct {
    21  		id    ssa.ID
    22  		which int
    23  	}]*ssa.Value)
    24  	for _, b := range f.Blocks {
    25  		for _, selector := range b.Values {
    26  			// Key fields for de-duplication
    27  			var tuple *ssa.Value
    28  			idx := 0
    29  			switch selector.Op {
    30  			default:
    31  				continue
    32  			case ssaop.OpSelect1:
    33  				idx = 1
    34  				fallthrough
    35  			case ssaop.OpSelect0:
    36  				tuple = selector.Args[0]
    37  				if !tuple.Type.IsTuple() {
    38  					f.Fatalf("arg of tuple selector %s is not a tuple: %s", selector.String(), tuple.LongString())
    39  				}
    40  			case ssaop.OpSelectN:
    41  				tuple = selector.Args[0]
    42  				idx = int(selector.AuxInt)
    43  				if !tuple.Type.IsResults() {
    44  					f.Fatalf("arg of result selector %s is not a results: %s", selector.String(), tuple.LongString())
    45  				}
    46  			}
    47  
    48  			// If there is a pre-existing selector in the target block then
    49  			// use that. Do this even if the selector is already in the
    50  			// target block to avoid duplicate tuple selectors.
    51  			key := struct {
    52  				id    ssa.ID
    53  				which int
    54  			}{tuple.ID, idx}
    55  			if t := selectors[key]; t != nil {
    56  				if selector != t {
    57  					selector.CopyOf(t)
    58  				}
    59  				continue
    60  			}
    61  
    62  			// If the selector is in the wrong block copy it into the target
    63  			// block.
    64  			if selector.Block != tuple.Block {
    65  				t := selector.CopyInto(tuple.Block)
    66  				selector.CopyOf(t)
    67  				selectors[key] = t
    68  				continue
    69  			}
    70  
    71  			// The selector is in the target block. Add it to the map so it
    72  			// cannot be duplicated.
    73  			selectors[key] = selector
    74  		}
    75  	}
    76  }
    77
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