Format impl witness instructions as part of the impl (#6485)

The impl's body block has to end before we make its ImplDecl
instruction, and the witness instructions come later, so they don't end
up in the body block. Currently they just end up in the enclosing (file,
typically, or class) scope block.

Add a new InstBlockId to Impl for holding witness instructions, and
explicitly insert them into that block. Then include those instructions
into the scope of the Impl for naming, and format them into the Impl
right after the body block.

This is based on #6484

Author: danakj

toolchain/check/handle_impl.cpp

@@ -281,6 +281,7 @@ static auto BuildImplDecl(Context& context, Parse::AnyImplDeclId node_id)
           // impl unusable for impl lookup.
           impl.witness_id = SemIR::ErrorInst::InstId;
         } else {
+          context.inst_block_stack().Push();
           // This makes either a placeholder witness table or a full witness
           // table. The full witness table is deferred to the impl definition
           // unless the declaration uses rewrite constraints to set values of
@@ -293,6 +294,7 @@ static auto BuildImplDecl(Context& context, Parse::AnyImplDeclId node_id)
           impl.witness_id = AddImplWitnessForDeclaration(
               context, node_id, impl,
               context.generics().GetSelfSpecific(impl.generic_id));
+          impl.witness_block_id = context.inst_block_stack().Pop();
         }
 
         FinishGenericDecl(context, node_id, impl.generic_id);

toolchain/check/testdata/as/basics.carbon

@@ -381,7 +381,7 @@ let n: {.x: ()} = {.x = ()} as {.x = ()};
 // CHECK:STDOUT:   %struct.948: %struct_type.x = struct_value (%empty_tuple) [concrete]
 // CHECK:STDOUT:   %X.val: %X = struct_value (%empty_tuple) [concrete]
 // CHECK:STDOUT:   %As.type.cd7: type = facet_type <@As, @As(%Y)> [concrete]
-// CHECK:STDOUT:   %As.impl_witness.362: <witness> = impl_witness file.%As.impl_witness_table.loc14 [concrete]
+// CHECK:STDOUT:   %As.impl_witness.362: <witness> = impl_witness @X.as.As.impl.%As.impl_witness_table [concrete]
 // CHECK:STDOUT:   %As.Convert.type.5a7: type = fn_type @As.Convert, @As(%Y) [concrete]
 // CHECK:STDOUT:   %X.as.As.impl.Convert.type: type = fn_type @X.as.As.impl.Convert [concrete]
 // CHECK:STDOUT:   %X.as.As.impl.Convert: %X.as.As.impl.Convert.type = struct_value () [concrete]

toolchain/check/testdata/as/var_init.carbon

@@ -34,7 +34,7 @@ fn Convert(t: ()) {
 // CHECK:STDOUT:   %empty_tuple.type: type = tuple_type () [concrete]
 // CHECK:STDOUT:   %empty_tuple: %empty_tuple.type = tuple_value () [concrete]
 // CHECK:STDOUT:   %ImplicitAs.type.37a: type = facet_type <@ImplicitAs, @ImplicitAs(%X)> [concrete]
-// CHECK:STDOUT:   %ImplicitAs.impl_witness: <witness> = impl_witness @X.%ImplicitAs.impl_witness_table [concrete]
+// CHECK:STDOUT:   %ImplicitAs.impl_witness: <witness> = impl_witness @empty_tuple.type.as.ImplicitAs.impl.%ImplicitAs.impl_witness_table [concrete]
 // CHECK:STDOUT:   %ImplicitAs.Convert.type.9f8: type = fn_type @ImplicitAs.Convert, @ImplicitAs(%X) [concrete]
 // CHECK:STDOUT:   %pattern_type.05f: type = pattern_type %X [concrete]
 // CHECK:STDOUT:   %empty_tuple.type.as.ImplicitAs.impl.Convert.type: type = fn_type @empty_tuple.type.as.ImplicitAs.impl.Convert [concrete]

toolchain/check/testdata/basics/include_in_dumps.carbon

@@ -124,7 +124,7 @@ fn F(c: C) { c.(I.Op)(); }
 // CHECK:STDOUT:   %I.assoc_type: type = assoc_entity_type @I [concrete]
 // CHECK:STDOUT:   %assoc0: %I.assoc_type = assoc_entity element0, @I.%I.Op.decl [concrete]
 // CHECK:STDOUT:   %C: type = class_type @C [concrete]
-// CHECK:STDOUT:   %I.impl_witness: <witness> = impl_witness @C.%I.impl_witness_table [concrete]
+// CHECK:STDOUT:   %I.impl_witness: <witness> = impl_witness @C.as.I.impl.%I.impl_witness_table [concrete]
 // CHECK:STDOUT:   %pattern_type.7c7: type = pattern_type %C [concrete]
 // CHECK:STDOUT:   %I.facet: %I.type = facet_value %C, (%I.impl_witness) [concrete]
 // CHECK:STDOUT: }

toolchain/check/testdata/builtins/type/destroy.carbon

@@ -41,15 +41,15 @@ fn F() {
 // CHECK:STDOUT:   %assoc0: %DestroyLike.assoc_type = assoc_entity element0, @DestroyLike.%DestroyLike.Op.decl [concrete]
 // CHECK:STDOUT:   %empty_tuple: %empty_tuple.type = tuple_value () [concrete]
 // CHECK:STDOUT:   %empty_struct_type: type = struct_type {} [concrete]
-// CHECK:STDOUT:   %DestroyLike.impl_witness.52f: <witness> = impl_witness file.%DestroyLike.impl_witness_table, @T.as.DestroyLike.impl(%empty_tuple.type) [concrete]
+// CHECK:STDOUT:   %DestroyLike.impl_witness.52f: <witness> = impl_witness @T.as.DestroyLike.impl.%DestroyLike.impl_witness_table, @T.as.DestroyLike.impl(%empty_tuple.type) [concrete]
 // CHECK:STDOUT:   %T.as.DestroyLike.impl.Op.type.6ca: type = fn_type @T.as.DestroyLike.impl.Op, @T.as.DestroyLike.impl(%empty_tuple.type) [concrete]
 // CHECK:STDOUT:   %T.as.DestroyLike.impl.Op.3ae: %T.as.DestroyLike.impl.Op.type.6ca = struct_value () [concrete]
 // CHECK:STDOUT:   %DestroyLike.facet.430: %DestroyLike.type = facet_value %empty_tuple.type, (%DestroyLike.impl_witness.52f) [concrete]
 // CHECK:STDOUT:   %.bcf: type = fn_type_with_self_type %DestroyLike.Op.type, %DestroyLike.facet.430 [concrete]
 // CHECK:STDOUT:   %T.as.DestroyLike.impl.Op.bound.f9f: <bound method> = bound_method file.%a.var, %T.as.DestroyLike.impl.Op.3ae [concrete]
 // CHECK:STDOUT:   %T.as.DestroyLike.impl.Op.specific_fn.38d: <specific function> = specific_function %T.as.DestroyLike.impl.Op.3ae, @T.as.DestroyLike.impl.Op(%empty_tuple.type) [concrete]
 // CHECK:STDOUT:   %bound_method.717: <bound method> = bound_method file.%a.var, %T.as.DestroyLike.impl.Op.specific_fn.38d [concrete]
-// CHECK:STDOUT:   %DestroyLike.impl_witness.409: <witness> = impl_witness file.%DestroyLike.impl_witness_table, @T.as.DestroyLike.impl(%empty_struct_type) [concrete]
+// CHECK:STDOUT:   %DestroyLike.impl_witness.409: <witness> = impl_witness @T.as.DestroyLike.impl.%DestroyLike.impl_witness_table, @T.as.DestroyLike.impl(%empty_struct_type) [concrete]
 // CHECK:STDOUT:   %T.as.DestroyLike.impl.Op.type.1f5: type = fn_type @T.as.DestroyLike.impl.Op, @T.as.DestroyLike.impl(%empty_struct_type) [concrete]
 // CHECK:STDOUT:   %T.as.DestroyLike.impl.Op.f28: %T.as.DestroyLike.impl.Op.type.1f5 = struct_value () [concrete]
 // CHECK:STDOUT:   %DestroyLike.facet.736: %DestroyLike.type = facet_value %empty_struct_type, (%DestroyLike.impl_witness.409) [concrete]

toolchain/check/testdata/class/generic/member_type.carbon

@@ -430,7 +430,7 @@ fn Test() -> i32 {
 // CHECK:STDOUT:   %Inner.assoc_type.be2: type = assoc_entity_type @Inner, @Inner(%T) [symbolic]
 // CHECK:STDOUT:   %assoc0.0a9: %Inner.assoc_type.be2 = assoc_entity element0, @Inner.%Inner.F.decl [symbolic]
 // CHECK:STDOUT:   %C.131: type = class_type @C, @C(%T) [symbolic]
-// CHECK:STDOUT:   %Inner.impl_witness.154: <witness> = impl_witness @C.%Inner.impl_witness_table, @C.as.Inner.impl(%T) [symbolic]
+// CHECK:STDOUT:   %Inner.impl_witness.154: <witness> = impl_witness @C.as.Inner.impl.%Inner.impl_witness_table, @C.as.Inner.impl(%T) [symbolic]
 // CHECK:STDOUT:   %require_complete.0f7: <witness> = require_complete_type %Inner.type.e0e [symbolic]
 // CHECK:STDOUT:   %pattern_type.fe7: type = pattern_type %C.131 [symbolic]
 // CHECK:STDOUT:   %C.as.Inner.impl.F.type.9a2: type = fn_type @C.as.Inner.impl.F, @C.as.Inner.impl(%T) [symbolic]
@@ -454,7 +454,7 @@ fn Test() -> i32 {
 // CHECK:STDOUT:   %Outer.d71: type = class_type @Outer, @Outer(%i32) [concrete]
 // CHECK:STDOUT:   %Inner.type.b33: type = facet_type <@Inner, @Inner(%i32)> [concrete]
 // CHECK:STDOUT:   %C.d3f: type = class_type @C, @C(%i32) [concrete]
-// CHECK:STDOUT:   %Inner.impl_witness.744: <witness> = impl_witness @D.%Inner.impl_witness_table [concrete]
+// CHECK:STDOUT:   %Inner.impl_witness.744: <witness> = impl_witness @D.as.Inner.impl.%Inner.impl_witness_table [concrete]
 // CHECK:STDOUT:   %Self.d74: %Inner.type.b33 = symbolic_binding Self, 1 [symbolic]
 // CHECK:STDOUT:   %Inner.F.type.c8b: type = fn_type @Inner.F, @Inner(%i32) [concrete]
 // CHECK:STDOUT:   %Inner.F.1cd: %Inner.F.type.c8b = struct_value () [concrete]
@@ -472,7 +472,7 @@ fn Test() -> i32 {
 // CHECK:STDOUT:   %pattern_type.129: type = pattern_type %C.d3f [concrete]
 // CHECK:STDOUT:   %empty_struct: %empty_struct_type = struct_value () [concrete]
 // CHECK:STDOUT:   %C.val: %C.d3f = struct_value () [concrete]
-// CHECK:STDOUT:   %Inner.impl_witness.2d0: <witness> = impl_witness @C.%Inner.impl_witness_table, @C.as.Inner.impl(%i32) [concrete]
+// CHECK:STDOUT:   %Inner.impl_witness.2d0: <witness> = impl_witness @C.as.Inner.impl.%Inner.impl_witness_table, @C.as.Inner.impl(%i32) [concrete]
 // CHECK:STDOUT:   %complete_type.75e: <witness> = complete_type_witness %Inner.type.b33 [concrete]
 // CHECK:STDOUT:   %C.as.Inner.impl.F.type.457: type = fn_type @C.as.Inner.impl.F, @C.as.Inner.impl(%i32) [concrete]
 // CHECK:STDOUT:   %C.as.Inner.impl.F.cc7: %C.as.Inner.impl.F.type.457 = struct_value () [concrete]
@@ -571,7 +571,7 @@ fn Test() -> i32 {
 // CHECK:STDOUT:   %T: type = symbolic_binding T, 0 [symbolic = %T (constants.%T)]
 // CHECK:STDOUT:   %C: type = class_type @C, @C(%T) [symbolic = %C (constants.%C.131)]
 // CHECK:STDOUT:   %Inner.type: type = facet_type <@Inner, @Inner(%T)> [symbolic = %Inner.type (constants.%Inner.type.e0e)]
-// CHECK:STDOUT:   %Inner.impl_witness: <witness> = impl_witness @C.%Inner.impl_witness_table, @C.as.Inner.impl(%T) [symbolic = %Inner.impl_witness (constants.%Inner.impl_witness.154)]
+// CHECK:STDOUT:   %Inner.impl_witness.loc10_19.2: <witness> = impl_witness %Inner.impl_witness_table, @C.as.Inner.impl(%T) [symbolic = %Inner.impl_witness.loc10_19.2 (constants.%Inner.impl_witness.154)]
 // CHECK:STDOUT:
 // CHECK:STDOUT: !definition:
 // CHECK:STDOUT:   %require_complete: <witness> = require_complete_type %Inner.type [symbolic = %require_complete (constants.%require_complete.0f7)]
@@ -595,13 +595,15 @@ fn Test() -> i32 {
 // CHECK:STDOUT:       %return.param: ref @C.as.Inner.impl.F.%T (%T) = out_param call_param1
 // CHECK:STDOUT:       %return: ref @C.as.Inner.impl.F.%T (%T) = return_slot %return.param
 // CHECK:STDOUT:     }
+// CHECK:STDOUT:     %Inner.impl_witness_table = impl_witness_table (%C.as.Inner.impl.F.decl), @C.as.Inner.impl [concrete]
+// CHECK:STDOUT:     %Inner.impl_witness.loc10_19.1: <witness> = impl_witness %Inner.impl_witness_table, @C.as.Inner.impl(constants.%T) [symbolic = %Inner.impl_witness.loc10_19.2 (constants.%Inner.impl_witness.154)]
 // CHECK:STDOUT:
 // CHECK:STDOUT:   !members:
 // CHECK:STDOUT:     .C = <poisoned>
 // CHECK:STDOUT:     .T = <poisoned>
 // CHECK:STDOUT:     .F = %C.as.Inner.impl.F.decl
 // CHECK:STDOUT:     .Inner = <poisoned>
-// CHECK:STDOUT:     witness = @C.%Inner.impl_witness
+// CHECK:STDOUT:     witness = %Inner.impl_witness.loc10_19.1
 // CHECK:STDOUT:   }
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
@@ -620,11 +622,13 @@ fn Test() -> i32 {
 // CHECK:STDOUT:     %return.param: ref %i32 = out_param call_param1
 // CHECK:STDOUT:     %return: ref %i32 = return_slot %return.param
 // CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Inner.impl_witness_table = impl_witness_table (%D.as.Inner.impl.F.decl), @D.as.Inner.impl [concrete]
+// CHECK:STDOUT:   %Inner.impl_witness: <witness> = impl_witness %Inner.impl_witness_table [concrete = constants.%Inner.impl_witness.744]
 // CHECK:STDOUT:
 // CHECK:STDOUT: !members:
 // CHECK:STDOUT:   .D = <poisoned>
 // CHECK:STDOUT:   .F = %D.as.Inner.impl.F.decl
-// CHECK:STDOUT:   witness = @D.%Inner.impl_witness
+// CHECK:STDOUT:   witness = %Inner.impl_witness
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: generic class @Outer(%T.loc4_13.2: type) {
@@ -657,8 +661,6 @@ fn Test() -> i32 {
 // CHECK:STDOUT:       %.loc10: type = specific_constant @Outer.%Inner.decl, @Outer(constants.%T) [symbolic = %Inner.type (constants.%Inner.type.e0e)]
 // CHECK:STDOUT:       %Inner.ref: type = name_ref Inner, %.loc10 [symbolic = %Inner.type (constants.%Inner.type.e0e)]
 // CHECK:STDOUT:     }
-// CHECK:STDOUT:     %Inner.impl_witness_table = impl_witness_table (@C.as.Inner.impl.%C.as.Inner.impl.F.decl), @C.as.Inner.impl [concrete]
-// CHECK:STDOUT:     %Inner.impl_witness: <witness> = impl_witness %Inner.impl_witness_table, @C.as.Inner.impl(constants.%T) [symbolic = @C.as.Inner.impl.%Inner.impl_witness (constants.%Inner.impl_witness.154)]
 // CHECK:STDOUT:     %complete_type: <witness> = complete_type_witness constants.%empty_struct_type [concrete = constants.%complete_type.357]
 // CHECK:STDOUT:     complete_type_witness = %complete_type
 // CHECK:STDOUT:
@@ -680,8 +682,6 @@ fn Test() -> i32 {
 // CHECK:STDOUT:     %.loc17: type = specific_constant @Outer.%Inner.decl, @Outer(constants.%i32) [concrete = constants.%Inner.type.b33]
 // CHECK:STDOUT:     %Inner.ref: type = name_ref Inner, %.loc17 [concrete = constants.%Inner.type.b33]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   %Inner.impl_witness_table = impl_witness_table (@D.as.Inner.impl.%D.as.Inner.impl.F.decl), @D.as.Inner.impl [concrete]
-// CHECK:STDOUT:   %Inner.impl_witness: <witness> = impl_witness %Inner.impl_witness_table [concrete = constants.%Inner.impl_witness.744]
 // CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness constants.%empty_struct_type [concrete = constants.%complete_type.357]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
 // CHECK:STDOUT:
@@ -820,7 +820,7 @@ fn Test() -> i32 {
 // CHECK:STDOUT:   %T => constants.%T
 // CHECK:STDOUT:   %C => constants.%C.131
 // CHECK:STDOUT:   %Inner.type => constants.%Inner.type.e0e
-// CHECK:STDOUT:   %Inner.impl_witness => constants.%Inner.impl_witness.154
+// CHECK:STDOUT:   %Inner.impl_witness.loc10_19.2 => constants.%Inner.impl_witness.154
 // CHECK:STDOUT:
 // CHECK:STDOUT: !definition:
 // CHECK:STDOUT:   %require_complete => constants.%require_complete.0f7
@@ -889,7 +889,7 @@ fn Test() -> i32 {
 // CHECK:STDOUT:   %T => constants.%i32
 // CHECK:STDOUT:   %C => constants.%C.d3f
 // CHECK:STDOUT:   %Inner.type => constants.%Inner.type.b33
-// CHECK:STDOUT:   %Inner.impl_witness => constants.%Inner.impl_witness.2d0
+// CHECK:STDOUT:   %Inner.impl_witness.loc10_19.2 => constants.%Inner.impl_witness.2d0
 // CHECK:STDOUT:
 // CHECK:STDOUT: !definition:
 // CHECK:STDOUT:   %require_complete => constants.%complete_type.75e

toolchain/check/testdata/class/virtual_modifiers.carbon

@@ -2003,7 +2003,7 @@ class T2(G2:! type) {
 // CHECK:STDOUT:   %ImplicitAs.type.cc7: type = generic_interface_type @ImplicitAs [concrete]
 // CHECK:STDOUT:   %ImplicitAs.generic: %ImplicitAs.type.cc7 = struct_value () [concrete]
 // CHECK:STDOUT:   %ImplicitAs.type.865: type = facet_type <@ImplicitAs, @ImplicitAs(%T1)> [concrete]
-// CHECK:STDOUT:   %ImplicitAs.impl_witness: <witness> = impl_witness file.%ImplicitAs.impl_witness_table [concrete]
+// CHECK:STDOUT:   %ImplicitAs.impl_witness: <witness> = impl_witness @T2.as.ImplicitAs.impl.%ImplicitAs.impl_witness_table [concrete]
 // CHECK:STDOUT:   %pattern_type.b8b: type = pattern_type %T2 [concrete]
 // CHECK:STDOUT:   %pattern_type.818: type = pattern_type %T1 [concrete]
 // CHECK:STDOUT:   %T2.as.ImplicitAs.impl.Convert.type: type = fn_type @T2.as.ImplicitAs.impl.Convert [concrete]
@@ -2055,8 +2055,6 @@ class T2(G2:! type) {
 // CHECK:STDOUT:     %T1.ref: type = name_ref T1, file.%T1.decl [concrete = constants.%T1]
 // CHECK:STDOUT:     %ImplicitAs.type: type = facet_type <@ImplicitAs, @ImplicitAs(constants.%T1)> [concrete = constants.%ImplicitAs.type.865]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   %ImplicitAs.impl_witness_table = impl_witness_table (@T2.as.ImplicitAs.impl.%T2.as.ImplicitAs.impl.Convert.decl), @T2.as.ImplicitAs.impl [concrete]
-// CHECK:STDOUT:   %ImplicitAs.impl_witness: <witness> = impl_witness %ImplicitAs.impl_witness_table [concrete = constants.%ImplicitAs.impl_witness]
 // CHECK:STDOUT:   %Base.decl: type = class_decl @Base [concrete = constants.%Base] {} {}
 // CHECK:STDOUT:   %Derived.decl: type = class_decl @Derived [concrete = constants.%Derived] {} {}
 // CHECK:STDOUT: }
@@ -2075,11 +2073,13 @@ class T2(G2:! type) {
 // CHECK:STDOUT:     %return.param: ref %T1 = out_param call_param1
 // CHECK:STDOUT:     %return: ref %T1 = return_slot %return.param
 // CHECK:STDOUT:   }
+// CHECK:STDOUT:   %ImplicitAs.impl_witness_table = impl_witness_table (%T2.as.ImplicitAs.impl.Convert.decl), @T2.as.ImplicitAs.impl [concrete]
+// CHECK:STDOUT:   %ImplicitAs.impl_witness: <witness> = impl_witness %ImplicitAs.impl_witness_table [concrete = constants.%ImplicitAs.impl_witness]
 // CHECK:STDOUT:
 // CHECK:STDOUT: !members:
 // CHECK:STDOUT:   .T1 = <poisoned>
 // CHECK:STDOUT:   .Convert = %T2.as.ImplicitAs.impl.Convert.decl
-// CHECK:STDOUT:   witness = file.%ImplicitAs.impl_witness
+// CHECK:STDOUT:   witness = %ImplicitAs.impl_witness
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @T1 {