Add SemIR Vtable instruction and usage (#4732)

Add a Vtable typed inst with a type_id (of the type this vtable applies
to) and list of virtual function decls (or import refs to function
object constants).

This doesn't add lowering/emission of the vtable, or usage when
initializing objects of the type.

Some questions in case they're interesting to discuss:
* is it right/worth having the type_id in the vtable? (probably makes it
easier to emit - using the type to get the class name to figure out the
mangled name for the vtable) perhaps it should be a ClassId?
* I'm thinking the logic in CheckCompleteClassType could be the place we
handle diagnostics for mismatched keywords (virtual/abstract for a
function that's already virtual/abstract, maybe checking for non-virtual
functions with the same name in a base class, or derived class functions
without `impl`, etc) - but we could move some of that to the moment we
walk the function decl, and record our findings in the function decl
(record the base function it overrides, or the index of the vtable to
slot to use when building the vtable at the end of the class)
* the Vtable typed inst has `constant_kind = InstConstantKind::Always`
and `is_lowered = false`, I think I added that in to workaround/address
some failures in lowering. And seems correct for this intermediate step
- I'll add lowering in a follow-up patch. But the constant_kind - what
should this be? We can just say all vtables are of VtableType (in which
case the `Always` constant kind sounds right to me) or we could have
them introduce a type with each virtual function as a named member,
even?

---------

Co-authored-by: Richard Smith <richard@metafoo.co.uk>
Co-authored-by: Jon Ross-Perkins <jperkins@google.com>

toolchain/check/testdata/function/declaration/no_prelude/extern.carbon

@@ -193,11 +193,6 @@ extern library "basic" fn F();
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%C
-// CHECK:STDOUT:   .F = %F.decl
-// CHECK:STDOUT:   .G = %G.decl
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @F();

toolchain/check/testdata/function/declaration/no_prelude/fail_import_incomplete_return.carbon

@@ -155,9 +155,6 @@ fn CallFAndGIncomplete() {
 // CHECK:STDOUT: class @D {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%D
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @ReturnCUnused() -> %C;
@@ -205,7 +202,6 @@ fn CallFAndGIncomplete() {
 // CHECK:STDOUT:   %import_ref.e1f: %ReturnDUsed.type = import_ref Main//incomplete_return, ReturnDUsed, loaded [template = constants.%ReturnDUsed]
 // CHECK:STDOUT:   %import_ref.2ce = import_ref Main//incomplete_return, Call, unloaded
 // CHECK:STDOUT:   %import_ref.8f2: <witness> = import_ref Main//incomplete_return, loc37_10, loaded [template = constants.%complete_type]
-// CHECK:STDOUT:   %import_ref.cab = import_ref Main//incomplete_return, inst16 [no loc], unloaded
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: file {
@@ -227,9 +223,6 @@ fn CallFAndGIncomplete() {
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @D [from "fail_incomplete_return.carbon"] {
 // CHECK:STDOUT:   complete_type_witness = imports.%import_ref.8f2
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = imports.%import_ref.cab
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @CallFAndGIncomplete() {

toolchain/check/testdata/function/declaration/no_prelude/name_poisoning.carbon

@@ -383,17 +383,11 @@ fn F() {
 // CHECK:STDOUT: class @C.1 {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%C.f79
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @C.2 {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%C.9f4
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @F1(%x.param_patt: %C.9f4);
@@ -439,9 +433,6 @@ fn F() {
 // CHECK:STDOUT: class @C {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%C
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @F1(%x.param_patt: %C);
@@ -480,17 +471,11 @@ fn F() {
 // CHECK:STDOUT: class @C {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%C
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @.1 {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%.fb7
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @F1(%x.param_patt: %C);
@@ -577,9 +562,6 @@ fn F() {
 // CHECK:STDOUT: class @C {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%C
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @F1(%x.param_patt: %C);
@@ -611,9 +593,6 @@ fn F() {
 // CHECK:STDOUT: class @C1 {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type.357]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%C1
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @D {
@@ -629,19 +608,11 @@ fn F() {
 // CHECK:STDOUT:   %.loc18: %D.elem = field_decl C1, element0 [template]
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %struct_type.C1 [template = constants.%complete_type.ec1]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%D
-// CHECK:STDOUT:   .F1 = %F1.decl
-// CHECK:STDOUT:   .C2 = %C2.decl
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @C2 {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type.357]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%C2
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @F1(%x.param_patt: %C1);
@@ -681,9 +652,6 @@ fn F() {
 // CHECK:STDOUT: class @C {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%C
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @F1(%x.param_patt: %C);
@@ -734,9 +702,6 @@ fn F() {
 // CHECK:STDOUT: class @C {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%C
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @F1() -> %C;
@@ -789,17 +754,11 @@ fn F() {
 // CHECK:STDOUT: class @C {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%C
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @.1 {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%.fb7
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @F1(%x.param_patt: %C);
@@ -823,13 +782,10 @@ fn F() {
 // CHECK:STDOUT:   %D2.type: type = facet_type <@D2> [template]
 // CHECK:STDOUT:   %Self.8cf: %D2.type = bind_symbolic_name Self, 0 [symbolic]
 // CHECK:STDOUT:   %D3.b65: type = class_type @D3 [template]
-// CHECK:STDOUT:   %D3.68e: type = class_type @D3, @D3(%Self.8cf) [symbolic]
 // CHECK:STDOUT:   %F.type: type = fn_type @F, @D3(%Self.8cf) [symbolic]
 // CHECK:STDOUT:   %F: %F.type = struct_value () [symbolic]
 // CHECK:STDOUT:   %.c1e: type = class_type @.1 [template]
-// CHECK:STDOUT:   %.180: type = class_type @.1, @.1(%Self.8cf) [symbolic]
 // CHECK:STDOUT:   %.9af: type = class_type @.2 [template]
-// CHECK:STDOUT:   %.5c1: type = class_type @.2, @.2(%Self.8cf) [symbolic]
 // CHECK:STDOUT:   %.6ae: type = class_type @.3 [template]
 // CHECK:STDOUT:   %.1c0: type = class_type @.4 [template]
 // CHECK:STDOUT:   %.type: type = facet_type <@.6> [template]
@@ -880,9 +836,6 @@ fn F() {
 // CHECK:STDOUT: class @C {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%C
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @D1 {
@@ -890,10 +843,6 @@ fn F() {
 // CHECK:STDOUT:   %.decl: type = class_decl @.3 [template = constants.%.6ae] {} {}
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%D1
-// CHECK:STDOUT:   .D2 = %D2.decl
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: generic class @D3(@D2.%Self: %D2.type) {
@@ -914,10 +863,6 @@ fn F() {
 // CHECK:STDOUT:     %.decl: type = class_decl @.1 [template = constants.%.c1e] {} {}
 // CHECK:STDOUT:     %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:     complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT:   !members:
-// CHECK:STDOUT:     .Self = constants.%D3.68e
-// CHECK:STDOUT:     .F = %F.decl
 // CHECK:STDOUT:   }
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
@@ -927,9 +872,6 @@ fn F() {
 // CHECK:STDOUT:   class {
 // CHECK:STDOUT:     %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:     complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT:   !members:
-// CHECK:STDOUT:     .Self = constants.%.180
 // CHECK:STDOUT:   }
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
@@ -939,34 +881,22 @@ fn F() {
 // CHECK:STDOUT:   class {
 // CHECK:STDOUT:     %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:     complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT:   !members:
-// CHECK:STDOUT:     .Self = constants.%.5c1
 // CHECK:STDOUT:   }
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @.3 {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%.6ae
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @.4 {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%.1c0
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @.5 {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%.4b5
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: generic fn @F(@D2.%Self: %D2.type) {
@@ -1006,9 +936,6 @@ fn F() {
 // CHECK:STDOUT: class @C {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%C
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: --- ignored_poison_in_import.carbon
@@ -1040,9 +967,6 @@ fn F() {
 // CHECK:STDOUT: class @C {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%C
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: --- poison.impl.carbon
@@ -1075,9 +999,6 @@ fn F() {
 // CHECK:STDOUT: class @C {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%C
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: --- using_poisoned_name_in_impl.carbon
@@ -1135,10 +1056,6 @@ fn F() {
 // CHECK:STDOUT:   %impl_witness: <witness> = impl_witness () [template = constants.%impl_witness]
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%X
-// CHECK:STDOUT:   extend @impl.%C.ref
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @F1(%x.param_patt: %C.type);
@@ -1152,7 +1069,6 @@ fn F() {
 // CHECK:STDOUT:   %B: %B.type = struct_value () [template]
 // CHECK:STDOUT:   %B.assoc_type: type = assoc_entity_type %A.type, %B.type [template]
 // CHECK:STDOUT:   %assoc0: %B.assoc_type = assoc_entity element0, @A.%B.decl [template]
-// CHECK:STDOUT:   %X: type = class_type @X [template]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: file {}
@@ -1172,10 +1088,6 @@ fn F() {
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @X {
 // CHECK:STDOUT:   complete_type_witness = invalid
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%X
-// CHECK:STDOUT:   extend <unexpected>.inst27.loc8_18
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: generic fn @B(@A.%Self: %A.type) {
@@ -1220,17 +1132,11 @@ fn F() {
 // CHECK:STDOUT: class @.1 {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%.a95
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @.2 {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%.fb7
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @F(%x.param_patt: <error>);
@@ -1260,9 +1166,6 @@ fn F() {
 // CHECK:STDOUT: class @A {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type.357]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%A
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @B {
@@ -1270,18 +1173,11 @@ fn F() {
 // CHECK:STDOUT:   %.decl: type = class_decl @.1 [template = constants.%.96d] {} {}
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %struct_type.v [template = constants.%complete_type.57e]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%B
-// CHECK:STDOUT:   .v = %.loc9
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @.1 {
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type.357]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%.96d
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @F() {