@@ -33,36 +33,60 @@ class ValueStoreNotPrintable {};
3333} // namespace Internal
3434
3535struct IdTag {
36- IdTag ()
37- : id_tag_(0 ),
38- initial_reserved_ids_ (std::numeric_limits<int32_t >::max()) {}
36+ IdTag () = default ;
37+
3938 explicit IdTag (int32_t id_index, int32_t initial_reserved_ids)
4039 : initial_reserved_ids_(initial_reserved_ids) {
4140 // Shift down by 1 to get out of the high bit to avoid using any negative
42- // ids, since they have special uses.
43- // Shift down by another 1 to free up the second highest bit for a marker to
44- // indicate whether the index is tagged (& needs to be untagged) or not.
45- // Add one to the index so it's not zero-based, to make it a bit less likely
46- // this doesn't collide with anything else (though with the
47- // second-highest-bit-tagging this might not be needed).
41+ // ids, since they have special uses. Shift down by another 1 to free up the
42+ // second highest bit for a marker to indicate whether the index is tagged
43+ // (& needs to be untagged) or not. Add one to the index so it's not
44+ // zero-based, to make it a bit less likely this doesn't collide with
45+ // anything else (though with the second-highest-bit-tagging this might not
46+ // be needed).
4847 id_tag_ = llvm::reverseBits ((((id_index + 1 ) << 1 ) | 1 ) << 1 );
4948 }
49+
5050 auto GetCheckIRId () const -> int32_t {
5151 return (llvm::reverseBits (id_tag_) >> 2 ) - 1 ;
5252 }
53+
5354 auto Apply (int32_t index) const -> int32_t {
5455 if (index < initial_reserved_ids_) {
5556 return index;
5657 }
57- // assert that id_tag_ doesn't have the second highest bit set
58+ // TODO: Assert that id_tag_ doesn't have the second highest bit set.
5859 return index ^ id_tag_;
5960 }
60- static auto DecomposeWithBestEffort (int32_t tagged_index)
61- -> std::pair<int32_t, int32_t> {
61+
62+ auto Remove (int32_t tagged_index) const -> int32_t {
63+ if (!HasTag (tagged_index)) {
64+ CARBON_DCHECK (tagged_index < initial_reserved_ids_,
65+ " This untagged index is outside the initial reserved ids "
66+ " and should have been tagged."
67+ return tagged_index;
68+ }
69+ auto index = tagged_index ^ id_tag_;
70+ CARBON_DCHECK (index >= initial_reserved_ids_,
71+ " When removing tagging bits, found an index that "
72+ " shouldn't've been tagged in the first place."
73+ return index;
74+ }
75+
76+ static auto HasTag (int32_t tagged_index) -> bool {
77+ return (llvm::reverseBits (2 ) & tagged_index) != 0 ;
78+ }
79+
80+ struct IrAndIndex {
81+ int32_t check_ir_id;
82+ int32_t index;
83+ };
84+
85+ static auto DecomposeWithBestEffort (int32_t tagged_index) -> IrAndIndex {
6286 if (tagged_index < 0 ) {
6387 return {-1 , tagged_index};
6488 }
65- if (( llvm::reverseBits ( 2 ) & tagged_index) == 0 ) {
89+ if (! HasTag ( tagged_index)) {
6690 return {-1 , tagged_index};
6791 }
6892 int length = 0 ;
@@ -86,25 +110,15 @@ struct IdTag {
86110 return {-1 , tagged_index};
87111 }
88112 auto index_mask = llvm::maskTrailingOnes<uint32_t >(location);
89- auto ir_id = (llvm::reverseBits (tagged_index & ~index_mask) >> 2 ) - 1 ;
113+ auto check_ir_id = (llvm::reverseBits (tagged_index & ~index_mask) >> 2 ) - 1 ;
90114 auto index = tagged_index & index_mask;
91- return {ir_id, index};
92- }
93- auto Remove (int32_t tagged_index) const -> int32_t {
94- if ((llvm::reverseBits (2 ) & tagged_index) == 0 ) {
95- CARBON_DCHECK (tagged_index < initial_reserved_ids_,
96- " This untagged index is outside the initial reserved ids "
97- " and should have been tagged."
98- return tagged_index;
99- }
100- auto index = tagged_index ^ id_tag_;
101- CARBON_DCHECK (index >= initial_reserved_ids_,
102- " When removing tagging bits, found an index that "
103- " shouldn't've been tagged in the first place."
104- return index;
115+ return {.check_ir_id = static_cast <int32_t >(check_ir_id),
116+ .index = static_cast <int32_t >(index)};
105117 }
106- int32_t id_tag_;
107- int32_t initial_reserved_ids_;
118+
119+ private:
120+ int32_t id_tag_ = 0 ;
121+ int32_t initial_reserved_ids_ = std::numeric_limits<int32_t >::max();
108122};
109123
110124// A simple wrapper for accumulating values, providing IDs to later retrieve the
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