Restructure action-dependence APIs (#7074)

- Rename `ActionIsDependent` to `ActionIsPerformable` (with negated
meaning), because that name is more concrete and, um, actionable.
- Replace `OperandIsDependent` with `OperandDependence`, which returns a
`ConstantDependence` instead of a bool. We need this additional
generality for handling form actions, where we sometimes need to ask
whether something has _any_ dependence, not just whether it has template
dependence.

toolchain/check/action.cpp

@@ -24,56 +24,59 @@ auto PerformAction(Context& context, SemIR::LocId loc_id,
        .source_id = action.inst_id});
 }
 
-static auto OperandIsDependent(Context& context, SemIR::ConstantId const_id)
-    -> bool {
+static auto OperandDependence(Context& context, SemIR::ConstantId const_id)
+    -> SemIR::ConstantDependence {
   // A type operand makes the instruction dependent if it is a
   // template-dependent constant.
   if (!const_id.is_symbolic()) {
-    return false;
+    return SemIR::ConstantDependence::None;
   }
-  return context.constant_values().GetSymbolicConstant(const_id).dependence ==
-         SemIR::ConstantDependence::Template;
+  return context.constant_values().GetSymbolicConstant(const_id).dependence;
 }
 
-auto OperandIsDependent(Context& context, SemIR::TypeId type_id) -> bool {
+auto OperandDependence(Context& context, SemIR::TypeId type_id)
+    -> SemIR::ConstantDependence {
   // A type operand makes the instruction dependent if it is a
   // template-dependent type.
-  return OperandIsDependent(context, context.types().GetConstantId(type_id));
+  return OperandDependence(context, context.types().GetConstantId(type_id));
 }
 
-auto OperandIsDependent(Context& context, SemIR::InstId inst_id) -> bool {
+auto OperandDependence(Context& context, SemIR::InstId inst_id)
+    -> SemIR::ConstantDependence {
   // An instruction operand makes the instruction dependent if its type or
   // constant value is dependent.
-  return OperandIsDependent(context, context.insts().Get(inst_id).type_id()) ||
-         OperandIsDependent(context, context.constant_values().Get(inst_id));
+  return std::max(
+      OperandDependence(context, context.insts().Get(inst_id).type_id()),
+      OperandDependence(context, context.constant_values().Get(inst_id)));
 }
 
-auto OperandIsDependent(Context& context, SemIR::TypeInstId inst_id) -> bool {
+auto OperandDependence(Context& context, SemIR::TypeInstId inst_id)
+    -> SemIR::ConstantDependence {
   // An instruction operand makes the instruction dependent if its type or
   // constant value is dependent. TypeInstId has type `TypeType` which is
   // concrete, so we only need to look at the constant value.
-  return OperandIsDependent(context, context.constant_values().Get(inst_id));
+  return OperandDependence(context, context.constant_values().Get(inst_id));
 }
 
-static auto OperandIsDependent(Context& context, SemIR::Inst::ArgAndKind arg)
-    -> bool {
+static auto OperandDependence(Context& context, SemIR::Inst::ArgAndKind arg)
+    -> SemIR::ConstantDependence {
   CARBON_KIND_SWITCH(arg) {
     case CARBON_KIND(SemIR::InstId inst_id): {
-      return OperandIsDependent(context, inst_id);
+      return OperandDependence(context, inst_id);
     }
 
     case CARBON_KIND(SemIR::MetaInstId inst_id): {
-      return OperandIsDependent(context, inst_id);
+      return OperandDependence(context, inst_id);
     }
 
     case CARBON_KIND(SemIR::TypeInstId inst_id): {
-      return OperandIsDependent(context, inst_id);
+      return OperandDependence(context, inst_id);
     }
 
     case SemIR::IdKind::None:
     case SemIR::IdKind::For<SemIR::AbsoluteInstId>:
     case SemIR::IdKind::For<SemIR::NameId>:
-      return false;
+      return SemIR::ConstantDependence::None;
 
     default:
       // TODO: Properly handle different argument kinds.
@@ -81,18 +84,20 @@ static auto OperandIsDependent(Context& context, SemIR::Inst::ArgAndKind arg)
   }
 }
 
-auto ActionIsDependent(Context& context, SemIR::Inst action_inst) -> bool {
+auto ActionIsPerformable(Context& context, SemIR::Inst action_inst) -> bool {
   if (auto refine_action = action_inst.TryAs<SemIR::RefineTypeAction>()) {
-    // `RefineTypeAction` can be performed whenever the type is non-dependent,
-    // even if we don't know the instruction yet.
-    return OperandIsDependent(context, refine_action->inst_type_inst_id);
+    // `RefineTypeAction` can be performed whenever the type is not template-
+    // dependent, even if we don't know the instruction yet.
+    return OperandDependence(context, refine_action->inst_type_inst_id) <
+           SemIR::ConstantDependence::Template;
   }
 
-  if (OperandIsDependent(context, action_inst.type_id())) {
-    return true;
-  }
-  return OperandIsDependent(context, action_inst.arg0_and_kind()) ||
-         OperandIsDependent(context, action_inst.arg1_and_kind());
+  return OperandDependence(context, action_inst.type_id()) <
+             SemIR::ConstantDependence::Template &&
+         OperandDependence(context, action_inst.arg0_and_kind()) <
+             SemIR::ConstantDependence::Template &&
+         OperandDependence(context, action_inst.arg1_and_kind()) <
+             SemIR::ConstantDependence::Template;
 }
 
 static auto AddDependentActionSpliceImpl(Context& context,
@@ -129,7 +134,8 @@ static auto RefineOperand(Context& context, SemIR::LocId loc_id,
 
     // If the type of the action argument is dependent, refine to an instruction
     // with a concrete type.
-    if (OperandIsDependent(context, inst.type_id())) {
+    if (OperandDependence(context, inst.type_id()) ==
+        SemIR::ConstantDependence::Template) {
       auto type_inst_id = context.types().GetTypeInstId(inst.type_id());
       inst_id = AddDependentActionSpliceImpl(
           context,

toolchain/check/action.h

@@ -28,21 +28,21 @@ auto PerformAction(Context& context, SemIR::LocId loc_id,
 auto PerformAction(Context& context, SemIR::LocId loc_id,
                    SemIR::RefineTypeAction action) -> SemIR::InstId;
 
-// Determines whether the given action depends on a template parameter in a way
-// that means it cannot be performed immediately.
-auto ActionIsDependent(Context& context, SemIR::Inst action_inst) -> bool;
-
-// Determines whether the given action operand depends on a template parameter
-// in a way that means the action cannot be performed immediately.
-auto OperandIsDependent(Context& context, SemIR::InstId inst_id) -> bool;
-
-// Determines whether the given action operand depends on a template parameter
-// in a way that means the action cannot be performed immediately.
-auto OperandIsDependent(Context& context, SemIR::TypeInstId inst_id) -> bool;
-
-// Determines whether the given type depends on a template parameter
-// in a way that means the action cannot be performed immediately.
-auto OperandIsDependent(Context& context, SemIR::TypeId type_id) -> bool;
+// Determines whether the given action can be performed immediately (i.e.
+// whether it is non-template-dependent).
+auto ActionIsPerformable(Context& context, SemIR::Inst action_inst) -> bool;
+
+// Returns the constant-dependence of `inst_id` (i.e. the maximum of the
+// constant-dependences of its type and its value).
+auto OperandDependence(Context& context, SemIR::InstId inst_id)
+    -> SemIR::ConstantDependence;
+auto OperandDependence(Context& context, SemIR::TypeInstId inst_id)
+    -> SemIR::ConstantDependence;
+
+// Returns the constant-dependence of `type_id` (i.e. the constant-dependence
+// of the corresponding type constant).
+auto OperandDependence(Context& context, SemIR::TypeId type_id)
+    -> SemIR::ConstantDependence;
 
 // Adds an instruction to the current block to splice in the result of
 // performing a dependent action.
@@ -66,9 +66,7 @@ template <typename ActionT>
 auto HandleAction(Context& context, SemIR::LocId loc_id, ActionT action_inst,
                   SemIR::TypeInstId result_type_inst_id =
                       SemIR::TypeInstId::None) -> SemIR::InstId {
-  if (ActionIsDependent(context, action_inst) ||
-      (result_type_inst_id.has_value() &&
-       OperandIsDependent(context, result_type_inst_id))) {
+  if (!ActionIsPerformable(context, action_inst)) {
     return AddDependentActionSplice(
         context, SemIR::LocIdAndInst(loc_id, action_inst), result_type_inst_id);
   }
@@ -93,7 +91,7 @@ auto EndPerformDelayedAction(Context& context, SemIR::InstId result_id)
 template <typename ActionT>
 auto PerformDelayedAction(Context& context, SemIR::LocId loc_id,
                           ActionT action_inst) -> SemIR::InstId {
-  if (ActionIsDependent(context, action_inst)) {
+  if (!ActionIsPerformable(context, action_inst)) {
     return SemIR::InstId::None;
   }
   Internal::BeginPerformDelayedAction(context);

toolchain/check/convert.cpp

@@ -1971,17 +1971,18 @@ auto Convert(Context& context, SemIR::LocId loc_id, SemIR::InstId expr_id,
   // didn't apply in the template definition.
   // TODO: Support this for targets other than `Value`.
   if (sem_ir.insts().Get(expr_id).type_id() != target.type_id &&
-      target.kind == ConversionTarget::Value &&
-      (OperandIsDependent(context, expr_id) ||
-       OperandIsDependent(context, target.type_id))) {
+      target.kind == ConversionTarget::Value) {
     auto target_type_inst_id = context.types().GetTypeInstId(target.type_id);
-    return AddDependentActionSplice(
-        context, loc_id,
-        SemIR::ConvertToValueAction{
-            .type_id = GetSingletonType(context, SemIR::InstType::TypeInstId),
-            .inst_id = expr_id,
-            .target_type_inst_id = target_type_inst_id},
-        target_type_inst_id);
+    SemIR::ConvertToValueAction convert_action = {
+        .type_id = GetSingletonType(context, SemIR::InstType::TypeInstId),
+        .inst_id = expr_id,
+        .target_type_inst_id = target_type_inst_id};
+    // We don't use `HandleAction` here because it would call `PerformAction`
+    // inline if it's performable, which would lead to infinite recursion.
+    if (!ActionIsPerformable(context, convert_action)) {
+      return AddDependentActionSplice(context, loc_id, convert_action,
+                                      target_type_inst_id);
+    }
   }
 
   // If this is not a builtin conversion, try an `ImplicitAs` conversion.

toolchain/check/eval.cpp

@@ -545,7 +545,8 @@ static auto GetConstantValue(EvalContext& eval_context,
   }
 
   // Otherwise, this is a normal instruction.
-  if (OperandIsDependent(eval_context.context(), inst_id)) {
+  if (OperandDependence(eval_context.context(), inst_id) ==
+      SemIR::ConstantDependence::Template) {
     *phase = LatestPhase(*phase, Phase::TemplateSymbolic);
   }
   return inst_id;