| 1 | // Copyright 2022 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 ssa |
| 6 | |
| 7 | import ( |
| 8 | "go/types" |
| 9 | |
| 10 | "golang.org/x/tools/internal/typeparams" |
| 11 | ) |
| 12 | |
| 13 | // Utilities for dealing with core types. |
| 14 | |
| 15 | // isBytestring returns true if T has the same terms as interface{[]byte | string}. |
| 16 | // These act like a core type for some operations: slice expressions, append and copy. |
| 17 | // |
| 18 | // See https://go.dev/ref/spec#Core_types for the details on bytestring. |
| 19 | func isBytestring(T types.Type) bool { |
| 20 | U := T.Underlying() |
| 21 | if _, ok := U.(*types.Interface); !ok { |
| 22 | return false |
| 23 | } |
| 24 | |
| 25 | tset := typeSetOf(U) |
| 26 | if tset.Len() != 2 { |
| 27 | return false |
| 28 | } |
| 29 | hasBytes, hasString := false, false |
| 30 | underIs(tset, func(t types.Type) bool { |
| 31 | switch { |
| 32 | case isString(t): |
| 33 | hasString = true |
| 34 | case isByteSlice(t): |
| 35 | hasBytes = true |
| 36 | } |
| 37 | return hasBytes || hasString |
| 38 | }) |
| 39 | return hasBytes && hasString |
| 40 | } |
| 41 | |
| 42 | // termList is a list of types. |
| 43 | type termList []*typeparams.Term // type terms of the type set |
| 44 | func (s termList) Len() int { return len(s) } |
| 45 | func (s termList) At(i int) types.Type { return s[i].Type() } |
| 46 | |
| 47 | // typeSetOf returns the type set of typ. Returns an empty typeset on an error. |
| 48 | func typeSetOf(typ types.Type) termList { |
| 49 | // This is a adaptation of x/exp/typeparams.NormalTerms which x/tools cannot depend on. |
| 50 | var terms []*typeparams.Term |
| 51 | var err error |
| 52 | switch typ := typ.(type) { |
| 53 | case *typeparams.TypeParam: |
| 54 | terms, err = typeparams.StructuralTerms(typ) |
| 55 | case *typeparams.Union: |
| 56 | terms, err = typeparams.UnionTermSet(typ) |
| 57 | case *types.Interface: |
| 58 | terms, err = typeparams.InterfaceTermSet(typ) |
| 59 | default: |
| 60 | // Common case. |
| 61 | // Specializing the len=1 case to avoid a slice |
| 62 | // had no measurable space/time benefit. |
| 63 | terms = []*typeparams.Term{typeparams.NewTerm(false, typ)} |
| 64 | } |
| 65 | |
| 66 | if err != nil { |
| 67 | return termList(nil) |
| 68 | } |
| 69 | return termList(terms) |
| 70 | } |
| 71 | |
| 72 | // underIs calls f with the underlying types of the specific type terms |
| 73 | // of s and reports whether all calls to f returned true. If there are |
| 74 | // no specific terms, underIs returns the result of f(nil). |
| 75 | func underIs(s termList, f func(types.Type) bool) bool { |
| 76 | if s.Len() == 0 { |
| 77 | return f(nil) |
| 78 | } |
| 79 | for i := 0; i < s.Len(); i++ { |
| 80 | u := s.At(i).Underlying() |
| 81 | if !f(u) { |
| 82 | return false |
| 83 | } |
| 84 | } |
| 85 | return true |
| 86 | } |
| 87 | |
| 88 | // indexType returns the element type and index mode of a IndexExpr over a type. |
| 89 | // It returns (nil, invalid) if the type is not indexable; this should never occur in a well-typed program. |
| 90 | func indexType(typ types.Type) (types.Type, indexMode) { |
| 91 | switch U := typ.Underlying().(type) { |
| 92 | case *types.Array: |
| 93 | return U.Elem(), ixArrVar |
| 94 | case *types.Pointer: |
| 95 | if arr, ok := U.Elem().Underlying().(*types.Array); ok { |
| 96 | return arr.Elem(), ixVar |
| 97 | } |
| 98 | case *types.Slice: |
| 99 | return U.Elem(), ixVar |
| 100 | case *types.Map: |
| 101 | return U.Elem(), ixMap |
| 102 | case *types.Basic: |
| 103 | return tByte, ixValue // must be a string |
| 104 | case *types.Interface: |
| 105 | tset := typeSetOf(U) |
| 106 | if tset.Len() == 0 { |
| 107 | return nil, ixInvalid // no underlying terms or error is empty. |
| 108 | } |
| 109 | |
| 110 | elem, mode := indexType(tset.At(0)) |
| 111 | for i := 1; i < tset.Len() && mode != ixInvalid; i++ { |
| 112 | e, m := indexType(tset.At(i)) |
| 113 | if !types.Identical(elem, e) { // if type checked, just a sanity check |
| 114 | return nil, ixInvalid |
| 115 | } |
| 116 | // Update the mode to the most constrained address type. |
| 117 | mode = mode.meet(m) |
| 118 | } |
| 119 | if mode != ixInvalid { |
| 120 | return elem, mode |
| 121 | } |
| 122 | } |
| 123 | return nil, ixInvalid |
| 124 | } |
| 125 | |
| 126 | // An indexMode specifies the (addressing) mode of an index operand. |
| 127 | // |
| 128 | // Addressing mode of an index operation is based on the set of |
| 129 | // underlying types. |
| 130 | // Hasse diagram of the indexMode meet semi-lattice: |
| 131 | // |
| 132 | // ixVar ixMap |
| 133 | // | | |
| 134 | // ixArrVar | |
| 135 | // | | |
| 136 | // ixValue | |
| 137 | // \ / |
| 138 | // ixInvalid |
| 139 | type indexMode byte |
| 140 | |
| 141 | const ( |
| 142 | ixInvalid indexMode = iota // index is invalid |
| 143 | ixValue // index is a computed value (not addressable) |
| 144 | ixArrVar // like ixVar, but index operand contains an array |
| 145 | ixVar // index is an addressable variable |
| 146 | ixMap // index is a map index expression (acts like a variable on lhs, commaok on rhs of an assignment) |
| 147 | ) |
| 148 | |
| 149 | // meet is the address type that is constrained by both x and y. |
| 150 | func (x indexMode) meet(y indexMode) indexMode { |
| 151 | if (x == ixMap || y == ixMap) && x != y { |
| 152 | return ixInvalid |
| 153 | } |
| 154 | // Use int representation and return min. |
| 155 | if x < y { |
| 156 | return y |
| 157 | } |
| 158 | return x |
| 159 | } |
| 160 |
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