Initial support for builtin functions. (#3803)

For now, a builtin function is defined by specifying a string literal
initializer in a function declaration:

```carbon
fn MyBuiltin(a: i32) -> i32 = "builtin.name";
```

End-to-end support is included for a sample `"int.add"` builtin
performing integer addition, covering constant evaluation and code
generation.

The implementation here needs substantial refactoring before we'll be
ready to start adding more builtins. That refactoring work will be
coming next. This change is aiming to checkpoint some incremental
progress.

toolchain/check/testdata/function/builtin/call.carbon

@@ -0,0 +1,43 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+fn Add(a: i32, b: i32) -> i32 = "int.add";
+
+var arr: [i32; Add(1, 2)];
+
+// CHECK:STDOUT: --- call.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: constants {
+// CHECK:STDOUT:   %.1: i32 = int_literal 1 [template]
+// CHECK:STDOUT:   %.2: i32 = int_literal 2 [template]
+// CHECK:STDOUT:   %.3: i32 = int_literal 3 [template]
+// CHECK:STDOUT:   %.4: type = array_type %.3, i32 [template]
+// CHECK:STDOUT:   %.5: type = ptr_type [i32; 3] [template]
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .Add = %Add
+// CHECK:STDOUT:     .arr = %arr
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Add: <function> = fn_decl @Add [template] {
+// CHECK:STDOUT:     %a.loc7_8.1: i32 = param a
+// CHECK:STDOUT:     @Add.%a: i32 = bind_name a, %a.loc7_8.1
+// CHECK:STDOUT:     %b.loc7_16.1: i32 = param b
+// CHECK:STDOUT:     @Add.%b: i32 = bind_name b, %b.loc7_16.1
+// CHECK:STDOUT:     %return.var: ref i32 = var <return slot>
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Add.ref: <function> = name_ref Add, %Add [template = %Add]
+// CHECK:STDOUT:   %.loc9_20: i32 = int_literal 1 [template = constants.%.1]
+// CHECK:STDOUT:   %.loc9_23: i32 = int_literal 2 [template = constants.%.2]
+// CHECK:STDOUT:   %.loc9_19: init i32 = call %Add.ref(%.loc9_20, %.loc9_23) [template = constants.%.3]
+// CHECK:STDOUT:   %.loc9_25: type = array_type %.loc9_19, i32 [template = constants.%.4]
+// CHECK:STDOUT:   %arr.var: ref [i32; 3] = var arr
+// CHECK:STDOUT:   %arr: ref [i32; 3] = bind_name arr, %arr.var
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @Add(%a: i32, %b: i32) -> i32 = "int.add";
+// CHECK:STDOUT:

toolchain/check/testdata/function/builtin/call_from_operator.carbon

@@ -0,0 +1,172 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+// --- core.carbon
+
+package Core api;
+
+interface Add {
+  fn Op[self: Self](other: Self) -> Self;
+}
+
+// --- user.carbon
+
+import Core;
+
+// TODO: This should be in `Core`, but currently impl lookup only looks in the
+// current file.
+impl i32 as Core.Add {
+  fn Op[self: i32](other: i32) -> i32 = "int.add";
+}
+
+var arr: [i32; 1 + 2] = (3, 4, 3 + 4);
+
+// CHECK:STDOUT: --- core.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: constants {
+// CHECK:STDOUT:   %.1: type = interface_type @Add [template]
+// CHECK:STDOUT:   %.2: type = assoc_entity_type @Add, <function> [template]
+// CHECK:STDOUT:   %.3: <associated <function> in Add> = assoc_entity element0, @Add.%Op [template]
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .Add = %Add.decl
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Add.decl: type = interface_decl @Add [template = constants.%.1] {}
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: interface @Add {
+// CHECK:STDOUT:   %Self: Add = bind_symbolic_name Self [symbolic]
+// CHECK:STDOUT:   %Op: <function> = fn_decl @Op [template] {
+// CHECK:STDOUT:     %Self.ref.loc5_15: Add = name_ref Self, %Self [symbolic = %Self]
+// CHECK:STDOUT:     %.loc5_15.1: type = facet_type_access %Self.ref.loc5_15 [symbolic = %Self]
+// CHECK:STDOUT:     %.loc5_15.2: type = converted %Self.ref.loc5_15, %.loc5_15.1 [symbolic = %Self]
+// CHECK:STDOUT:     %self.loc5_9.1: Self = param self
+// CHECK:STDOUT:     %self.loc5_9.2: Self = bind_name self, %self.loc5_9.1
+// CHECK:STDOUT:     %Self.ref.loc5_28: Add = name_ref Self, %Self [symbolic = %Self]
+// CHECK:STDOUT:     %.loc5_28.1: type = facet_type_access %Self.ref.loc5_28 [symbolic = %Self]
+// CHECK:STDOUT:     %.loc5_28.2: type = converted %Self.ref.loc5_28, %.loc5_28.1 [symbolic = %Self]
+// CHECK:STDOUT:     %other.loc5_21.1: Self = param other
+// CHECK:STDOUT:     %other.loc5_21.2: Self = bind_name other, %other.loc5_21.1
+// CHECK:STDOUT:     %Self.ref.loc5_37: Add = name_ref Self, %Self [symbolic = %Self]
+// CHECK:STDOUT:     %.loc5_37.1: type = facet_type_access %Self.ref.loc5_37 [symbolic = %Self]
+// CHECK:STDOUT:     %.loc5_37.2: type = converted %Self.ref.loc5_37, %.loc5_37.1 [symbolic = %Self]
+// CHECK:STDOUT:     %return.var: ref Self = var <return slot>
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %.loc5_41: <associated <function> in Add> = assoc_entity element0, %Op [template = constants.%.3]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = %Self
+// CHECK:STDOUT:   .Op = %.loc5_41
+// CHECK:STDOUT:   witness = (%Op)
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @Op[@Add.%self.loc5_9.2: Self](@Add.%other.loc5_21.2: Self) -> Self;
+// CHECK:STDOUT:
+// CHECK:STDOUT: --- user.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: constants {
+// CHECK:STDOUT:   %.1: type = interface_type @Add [template]
+// CHECK:STDOUT:   %.2: <witness> = interface_witness (@impl.%Op) [template]
+// CHECK:STDOUT:   %.3: i32 = int_literal 1 [template]
+// CHECK:STDOUT:   %.4: i32 = int_literal 2 [template]
+// CHECK:STDOUT:   %.5: type = assoc_entity_type @Add, <function> [template]
+// CHECK:STDOUT:   %.6: <associated <function> in Add> = assoc_entity element0, file.%import_ref.6 [template]
+// CHECK:STDOUT:   %.7: <bound method> = bound_method %.3, @impl.%Op [template]
+// CHECK:STDOUT:   %.8: i32 = int_literal 3 [template]
+// CHECK:STDOUT:   %.9: type = array_type %.8, i32 [template]
+// CHECK:STDOUT:   %.10: type = ptr_type [i32; 3] [template]
+// CHECK:STDOUT:   %.11: i32 = int_literal 3 [template]
+// CHECK:STDOUT:   %.12: i32 = int_literal 4 [template]
+// CHECK:STDOUT:   %.13: <bound method> = bound_method %.11, @impl.%Op [template]
+// CHECK:STDOUT:   %.14: i32 = int_literal 7 [template]
+// CHECK:STDOUT:   %.15: type = tuple_type (i32, i32, i32) [template]
+// CHECK:STDOUT:   %.16: i32 = int_literal 0 [template]
+// CHECK:STDOUT:   %.17: i32 = int_literal 1 [template]
+// CHECK:STDOUT:   %.18: i32 = int_literal 2 [template]
+// CHECK:STDOUT:   %.19: [i32; 3] = tuple_value (%.11, %.12, %.14) [template]
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .Core = %Core
+// CHECK:STDOUT:     .arr = %arr
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Core: <namespace> = namespace [template] {}
+// CHECK:STDOUT:   %import_ref.1: type = import_ref ir1, inst+1, used [template = constants.%.1]
+// CHECK:STDOUT:   %import_ref.2: <associated <function> in Add> = import_ref ir1, inst+20, used [template = constants.%.6]
+// CHECK:STDOUT:   %import_ref.3 = import_ref ir1, inst+3, unused
+// CHECK:STDOUT:   %import_ref.4: <function> = import_ref ir1, inst+18, used [template = imports.%Op]
+// CHECK:STDOUT:   impl_decl @impl {
+// CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, %Core [template = %Core]
+// CHECK:STDOUT:     %Add.decl: invalid = interface_decl @Add [template = constants.%.1] {}
+// CHECK:STDOUT:     %Add.ref: type = name_ref Add, %import_ref.1 [template = constants.%.1]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %.loc10_16: i32 = int_literal 1 [template = constants.%.3]
+// CHECK:STDOUT:   %.loc10_20: i32 = int_literal 2 [template = constants.%.4]
+// CHECK:STDOUT:   %import_ref.5: type = import_ref ir1, inst+1, used [template = constants.%.1]
+// CHECK:STDOUT:   %import_ref.6 = import_ref ir1, inst+18, unused
+// CHECK:STDOUT:   %.1: <function> = interface_witness_access @impl.%.1, element0 [template = @impl.%Op]
+// CHECK:STDOUT:   %.loc10_18.1: <bound method> = bound_method %.loc10_16, %.1 [template = constants.%.7]
+// CHECK:STDOUT:   %.loc10_18.2: init i32 = call %.loc10_18.1(%.loc10_16, %.loc10_20) [template = constants.%.8]
+// CHECK:STDOUT:   %.loc10_21: type = array_type %.loc10_18.2, i32 [template = constants.%.9]
+// CHECK:STDOUT:   %arr.var: ref [i32; 3] = var arr
+// CHECK:STDOUT:   %arr: ref [i32; 3] = bind_name arr, %arr.var
+// CHECK:STDOUT:   %import_ref.7: type = import_ref ir1, inst+1, used [template = constants.%.1]
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: interface @Add {
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Op = file.%import_ref.2
+// CHECK:STDOUT:   .Self = file.%import_ref.3
+// CHECK:STDOUT:   witness = (file.%import_ref.4)
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: impl @impl: i32 as Add {
+// CHECK:STDOUT:   %Op: <function> = fn_decl @Op.1 [template] {
+// CHECK:STDOUT:     %self.loc7_9.1: i32 = param self
+// CHECK:STDOUT:     %self.loc7_9.2: i32 = bind_name self, %self.loc7_9.1
+// CHECK:STDOUT:     %other.loc7_20.1: i32 = param other
+// CHECK:STDOUT:     %other.loc7_20.2: i32 = bind_name other, %other.loc7_20.1
+// CHECK:STDOUT:     %return.var: ref i32 = var <return slot>
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %.1: <witness> = interface_witness (%Op) [template = constants.%.2]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Op = %Op
+// CHECK:STDOUT:   witness = %.1
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @Op.1[@impl.%self.loc7_9.2: i32](@impl.%other.loc7_20.2: i32) -> i32 = "int.add";
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @Op.2[%self: Self](%other: Self) -> Self;
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @__global_init() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   %.loc10_26: i32 = int_literal 3 [template = constants.%.11]
+// CHECK:STDOUT:   %.loc10_29: i32 = int_literal 4 [template = constants.%.12]
+// CHECK:STDOUT:   %.loc10_32: i32 = int_literal 3 [template = constants.%.11]
+// CHECK:STDOUT:   %.loc10_36: i32 = int_literal 4 [template = constants.%.12]
+// CHECK:STDOUT:   %.1: <function> = interface_witness_access @impl.%.1, element0 [template = @impl.%Op]
+// CHECK:STDOUT:   %.loc10_34.1: <bound method> = bound_method %.loc10_32, %.1 [template = constants.%.13]
+// CHECK:STDOUT:   %.loc10_34.2: init i32 = call %.loc10_34.1(%.loc10_32, %.loc10_36) [template = constants.%.14]
+// CHECK:STDOUT:   %.loc10_37.1: (i32, i32, i32) = tuple_literal (%.loc10_26, %.loc10_29, %.loc10_34.2)
+// CHECK:STDOUT:   %.loc10_37.2: i32 = int_literal 0 [template = constants.%.16]
+// CHECK:STDOUT:   %.loc10_37.3: ref i32 = array_index file.%arr.var, %.loc10_37.2
+// CHECK:STDOUT:   %.loc10_37.4: init i32 = initialize_from %.loc10_26 to %.loc10_37.3 [template = constants.%.11]
+// CHECK:STDOUT:   %.loc10_37.5: i32 = int_literal 1 [template = constants.%.17]
+// CHECK:STDOUT:   %.loc10_37.6: ref i32 = array_index file.%arr.var, %.loc10_37.5
+// CHECK:STDOUT:   %.loc10_37.7: init i32 = initialize_from %.loc10_29 to %.loc10_37.6 [template = constants.%.12]
+// CHECK:STDOUT:   %.loc10_37.8: i32 = int_literal 2 [template = constants.%.18]
+// CHECK:STDOUT:   %.loc10_37.9: ref i32 = array_index file.%arr.var, %.loc10_37.8
+// CHECK:STDOUT:   %.loc10_37.10: init i32 = initialize_from %.loc10_34.2 to %.loc10_37.9 [template = constants.%.14]
+// CHECK:STDOUT:   %.loc10_37.11: init [i32; 3] = array_init (%.loc10_37.4, %.loc10_37.7, %.loc10_37.10) to file.%arr.var [template = constants.%.19]
+// CHECK:STDOUT:   %.loc10_37.12: init [i32; 3] = converted %.loc10_37.1, %.loc10_37.11 [template = constants.%.19]
+// CHECK:STDOUT:   assign file.%arr.var, %.loc10_37.12
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:

toolchain/check/testdata/function/builtin/definition.carbon

@@ -0,0 +1,25 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+fn Add(a: i32, b: i32) -> i32 = "int.add";
+
+// CHECK:STDOUT: --- definition.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .Add = %Add
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Add: <function> = fn_decl @Add [template] {
+// CHECK:STDOUT:     %a.loc7_8.1: i32 = param a
+// CHECK:STDOUT:     @Add.%a: i32 = bind_name a, %a.loc7_8.1
+// CHECK:STDOUT:     %b.loc7_16.1: i32 = param b
+// CHECK:STDOUT:     @Add.%b: i32 = bind_name b, %b.loc7_16.1
+// CHECK:STDOUT:     %return.var: ref i32 = var <return slot>
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @Add(%a: i32, %b: i32) -> i32 = "int.add";
+// CHECK:STDOUT:

toolchain/check/testdata/function/builtin/fail_redefined.carbon

@@ -0,0 +1,99 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+fn A(n: i32, m: i32) -> i32 = "int.add";
+// CHECK:STDERR: fail_redefined.carbon:[[@LINE+6]]:1: ERROR: Redefinition of function A.
+// CHECK:STDERR: fn A(n: i32, m: i32) -> i32 { return n; }
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR: fail_redefined.carbon:[[@LINE-4]]:1: Previously defined here.
+// CHECK:STDERR: fn A(n: i32, m: i32) -> i32 = "int.add";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+fn A(n: i32, m: i32) -> i32 { return n; }
+
+fn B(n: i32, m: i32) -> i32 { return n; }
+// CHECK:STDERR: fail_redefined.carbon:[[@LINE+6]]:1: ERROR: Redefinition of function B.
+// CHECK:STDERR: fn B(n: i32, m: i32) -> i32 = "int.add";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR: fail_redefined.carbon:[[@LINE-4]]:1: Previously defined here.
+// CHECK:STDERR: fn B(n: i32, m: i32) -> i32 { return n; }
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+fn B(n: i32, m: i32) -> i32 = "int.add";
+
+fn C(n: i32, m: i32) -> i32 = "int.add";
+// CHECK:STDERR: fail_redefined.carbon:[[@LINE+6]]:1: ERROR: Redefinition of function C.
+// CHECK:STDERR: fn C(n: i32, m: i32) -> i32 = "int.add";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR: fail_redefined.carbon:[[@LINE-4]]:1: Previously defined here.
+// CHECK:STDERR: fn C(n: i32, m: i32) -> i32 = "int.add";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+fn C(n: i32, m: i32) -> i32 = "int.add";
+
+// CHECK:STDOUT: --- fail_redefined.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .A = %A.loc7
+// CHECK:STDOUT:     .B = %B.loc16
+// CHECK:STDOUT:     .C = %C.loc25
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %A.loc7: <function> = fn_decl @A [template] {
+// CHECK:STDOUT:     %n.loc7_6.1: i32 = param n
+// CHECK:STDOUT:     @A.%n: i32 = bind_name n, %n.loc7_6.1
+// CHECK:STDOUT:     %m.loc7_14.1: i32 = param m
+// CHECK:STDOUT:     @A.%m: i32 = bind_name m, %m.loc7_14.1
+// CHECK:STDOUT:     %return.var.loc7: ref i32 = var <return slot>
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %A.loc14: <function> = fn_decl @A [template] {
+// CHECK:STDOUT:     %n.loc14_6.1: i32 = param n
+// CHECK:STDOUT:     %n.loc14_6.2: i32 = bind_name n, %n.loc14_6.1
+// CHECK:STDOUT:     %m.loc14_14.1: i32 = param m
+// CHECK:STDOUT:     %m.loc14_14.2: i32 = bind_name m, %m.loc14_14.1
+// CHECK:STDOUT:     %return.var.loc14: ref i32 = var <return slot>
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %B.loc16: <function> = fn_decl @B [template] {
+// CHECK:STDOUT:     %n.loc16_6.1: i32 = param n
+// CHECK:STDOUT:     @B.%n: i32 = bind_name n, %n.loc16_6.1
+// CHECK:STDOUT:     %m.loc16_14.1: i32 = param m
+// CHECK:STDOUT:     @B.%m: i32 = bind_name m, %m.loc16_14.1
+// CHECK:STDOUT:     %return.var.loc16: ref i32 = var <return slot>
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %B.loc23: <function> = fn_decl @B [template] {
+// CHECK:STDOUT:     %n.loc23_6.1: i32 = param n
+// CHECK:STDOUT:     %n.loc23_6.2: i32 = bind_name n, %n.loc23_6.1
+// CHECK:STDOUT:     %m.loc23_14.1: i32 = param m
+// CHECK:STDOUT:     %m.loc23_14.2: i32 = bind_name m, %m.loc23_14.1
+// CHECK:STDOUT:     %return.var.loc23: ref i32 = var <return slot>
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %C.loc25: <function> = fn_decl @C [template] {
+// CHECK:STDOUT:     %n.loc25_6.1: i32 = param n
+// CHECK:STDOUT:     @C.%n: i32 = bind_name n, %n.loc25_6.1
+// CHECK:STDOUT:     %m.loc25_14.1: i32 = param m
+// CHECK:STDOUT:     @C.%m: i32 = bind_name m, %m.loc25_14.1
+// CHECK:STDOUT:     %return.var.loc25: ref i32 = var <return slot>
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %C.loc32: <function> = fn_decl @C [template] {
+// CHECK:STDOUT:     %n.loc32_6.1: i32 = param n
+// CHECK:STDOUT:     %n.loc32_6.2: i32 = bind_name n, %n.loc32_6.1
+// CHECK:STDOUT:     %m.loc32_14.1: i32 = param m
+// CHECK:STDOUT:     %m.loc32_14.2: i32 = bind_name m, %m.loc32_14.1
+// CHECK:STDOUT:     %return.var.loc32: ref i32 = var <return slot>
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @A(%n: i32, %m: i32) -> i32 = "int.add" {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   %n.ref: i32 = name_ref n, file.%n.loc14_6.2
+// CHECK:STDOUT:   return %n.ref
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @B(%n: i32, %m: i32) -> i32 = "int.add" {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   %n.ref: i32 = name_ref n, %n
+// CHECK:STDOUT:   return %n.ref
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @C(%n: i32, %m: i32) -> i32 = "int.add";
+// CHECK:STDOUT:

toolchain/check/testdata/function/builtin/fail_unknown.carbon

@@ -0,0 +1,22 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+// CHECK:STDERR: fail_unknown.carbon:[[@LINE+3]]:23: ERROR: Unknown builtin function name "unknown.builtin.name".
+// CHECK:STDERR: fn UnknownBuiltin() = "unknown.builtin.name";
+// CHECK:STDERR:                       ^~~~~~~~~~~~~~~~~~~~~~
+fn UnknownBuiltin() = "unknown.builtin.name";
+
+// CHECK:STDOUT: --- fail_unknown.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .UnknownBuiltin = %UnknownBuiltin
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %UnknownBuiltin: <function> = fn_decl @UnknownBuiltin [template] {}
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @UnknownBuiltin();
+// CHECK:STDOUT:

toolchain/check/testdata/function/builtin/import.carbon

@@ -0,0 +1,91 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+// --- core.carbon
+
+package Core api;
+
+fn Add(a: i32, b: i32) -> i32 = "int.add";
+
+// --- use.carbon
+
+import Core;
+
+var arr: [i32; Core.Add(1, 2)] = (1, 2, 3);
+
+// CHECK:STDOUT: --- core.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .Add = %Add
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Add: <function> = fn_decl @Add [template] {
+// CHECK:STDOUT:     %a.loc4_8.1: i32 = param a
+// CHECK:STDOUT:     @Add.%a: i32 = bind_name a, %a.loc4_8.1
+// CHECK:STDOUT:     %b.loc4_16.1: i32 = param b
+// CHECK:STDOUT:     @Add.%b: i32 = bind_name b, %b.loc4_16.1
+// CHECK:STDOUT:     %return.var: ref i32 = var <return slot>
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @Add(%a: i32, %b: i32) -> i32 = "int.add";
+// CHECK:STDOUT:
+// CHECK:STDOUT: --- use.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: constants {
+// CHECK:STDOUT:   %.1: i32 = int_literal 1 [template]
+// CHECK:STDOUT:   %.2: i32 = int_literal 2 [template]
+// CHECK:STDOUT:   %.3: i32 = int_literal 3 [template]
+// CHECK:STDOUT:   %.4: type = array_type %.3, i32 [template]
+// CHECK:STDOUT:   %.5: type = ptr_type [i32; 3] [template]
+// CHECK:STDOUT:   %.6: i32 = int_literal 3 [template]
+// CHECK:STDOUT:   %.7: type = tuple_type (i32, i32, i32) [template]
+// CHECK:STDOUT:   %.8: i32 = int_literal 0 [template]
+// CHECK:STDOUT:   %.9: i32 = int_literal 1 [template]
+// CHECK:STDOUT:   %.10: i32 = int_literal 2 [template]
+// CHECK:STDOUT:   %.11: [i32; 3] = tuple_value (%.1, %.2, %.6) [template]
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .Core = %Core
+// CHECK:STDOUT:     .arr = %arr
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Core: <namespace> = namespace [template] {}
+// CHECK:STDOUT:   %Core.ref: <namespace> = name_ref Core, %Core [template = %Core]
+// CHECK:STDOUT:   %import_ref: <function> = import_ref ir1, inst+6, used [template = imports.%Add]
+// CHECK:STDOUT:   %Add.ref: <function> = name_ref Add, %import_ref [template = imports.%Add]
+// CHECK:STDOUT:   %.loc4_25: i32 = int_literal 1 [template = constants.%.1]
+// CHECK:STDOUT:   %.loc4_28: i32 = int_literal 2 [template = constants.%.2]
+// CHECK:STDOUT:   %.loc4_24: init i32 = call %Add.ref(%.loc4_25, %.loc4_28) [template = constants.%.3]
+// CHECK:STDOUT:   %.loc4_30: type = array_type %.loc4_24, i32 [template = constants.%.4]
+// CHECK:STDOUT:   %arr.var: ref [i32; 3] = var arr
+// CHECK:STDOUT:   %arr: ref [i32; 3] = bind_name arr, %arr.var
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @Add(%a: i32, %b: i32) -> i32 = "int.add";
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @__global_init() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   %.loc4_35: i32 = int_literal 1 [template = constants.%.1]
+// CHECK:STDOUT:   %.loc4_38: i32 = int_literal 2 [template = constants.%.2]
+// CHECK:STDOUT:   %.loc4_41: i32 = int_literal 3 [template = constants.%.6]
+// CHECK:STDOUT:   %.loc4_42.1: (i32, i32, i32) = tuple_literal (%.loc4_35, %.loc4_38, %.loc4_41)
+// CHECK:STDOUT:   %.loc4_42.2: i32 = int_literal 0 [template = constants.%.8]
+// CHECK:STDOUT:   %.loc4_42.3: ref i32 = array_index file.%arr.var, %.loc4_42.2
+// CHECK:STDOUT:   %.loc4_42.4: init i32 = initialize_from %.loc4_35 to %.loc4_42.3 [template = constants.%.1]
+// CHECK:STDOUT:   %.loc4_42.5: i32 = int_literal 1 [template = constants.%.9]
+// CHECK:STDOUT:   %.loc4_42.6: ref i32 = array_index file.%arr.var, %.loc4_42.5
+// CHECK:STDOUT:   %.loc4_42.7: init i32 = initialize_from %.loc4_38 to %.loc4_42.6 [template = constants.%.2]
+// CHECK:STDOUT:   %.loc4_42.8: i32 = int_literal 2 [template = constants.%.10]
+// CHECK:STDOUT:   %.loc4_42.9: ref i32 = array_index file.%arr.var, %.loc4_42.8
+// CHECK:STDOUT:   %.loc4_42.10: init i32 = initialize_from %.loc4_41 to %.loc4_42.9 [template = constants.%.6]
+// CHECK:STDOUT:   %.loc4_42.11: init [i32; 3] = array_init (%.loc4_42.4, %.loc4_42.7, %.loc4_42.10) to file.%arr.var [template = constants.%.11]
+// CHECK:STDOUT:   %.loc4_42.12: init [i32; 3] = converted %.loc4_42.1, %.loc4_42.11 [template = constants.%.11]
+// CHECK:STDOUT:   assign file.%arr.var, %.loc4_42.12
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:

toolchain/check/testdata/function/builtin/method.carbon

@@ -0,0 +1,97 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+interface I {
+  fn F[self: Self](other: Self) -> Self;
+}
+
+impl i32 as I {
+  fn F[self: i32](other: i32) -> i32 = "int.add";
+}
+
+var arr: [i32; 1.(I.F)(2)];
+
+// CHECK:STDOUT: --- method.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: constants {
+// CHECK:STDOUT:   %.1: type = interface_type @I [template]
+// CHECK:STDOUT:   %.2: type = assoc_entity_type @I, <function> [template]
+// CHECK:STDOUT:   %.3: <associated <function> in I> = assoc_entity element0, @I.%F [template]
+// CHECK:STDOUT:   %.4: <witness> = interface_witness (@impl.%F) [template]
+// CHECK:STDOUT:   %.5: i32 = int_literal 1 [template]
+// CHECK:STDOUT:   %.6: <bound method> = bound_method %.5, @impl.%F [template]
+// CHECK:STDOUT:   %.7: i32 = int_literal 2 [template]
+// CHECK:STDOUT:   %.8: i32 = int_literal 3 [template]
+// CHECK:STDOUT:   %.9: type = array_type %.8, i32 [template]
+// CHECK:STDOUT:   %.10: type = ptr_type [i32; 3] [template]
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .I = %I.decl
+// CHECK:STDOUT:     .arr = %arr
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %I.decl: type = interface_decl @I [template = constants.%.1] {}
+// CHECK:STDOUT:   impl_decl @impl {
+// CHECK:STDOUT:     %I.ref.loc11: type = name_ref I, %I.decl [template = constants.%.1]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %.loc15_16: i32 = int_literal 1 [template = constants.%.5]
+// CHECK:STDOUT:   %I.ref.loc15: type = name_ref I, %I.decl [template = constants.%.1]
+// CHECK:STDOUT:   %F.ref: <associated <function> in I> = name_ref F, @I.%.loc8_40 [template = constants.%.3]
+// CHECK:STDOUT:   %.1: <function> = interface_witness_access @impl.%.1, element0 [template = @impl.%F]
+// CHECK:STDOUT:   %.loc15_17: <bound method> = bound_method %.loc15_16, %.1 [template = constants.%.6]
+// CHECK:STDOUT:   %.loc15_24: i32 = int_literal 2 [template = constants.%.7]
+// CHECK:STDOUT:   %.loc15_23: init i32 = call %.loc15_17(%.loc15_16, %.loc15_24) [template = constants.%.8]
+// CHECK:STDOUT:   %.loc15_26: type = array_type %.loc15_23, i32 [template = constants.%.9]
+// CHECK:STDOUT:   %arr.var: ref [i32; 3] = var arr
+// CHECK:STDOUT:   %arr: ref [i32; 3] = bind_name arr, %arr.var
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: interface @I {
+// CHECK:STDOUT:   %Self: I = bind_symbolic_name Self [symbolic]
+// CHECK:STDOUT:   %F: <function> = fn_decl @F.1 [template] {
+// CHECK:STDOUT:     %Self.ref.loc8_14: I = name_ref Self, %Self [symbolic = %Self]
+// CHECK:STDOUT:     %.loc8_14.1: type = facet_type_access %Self.ref.loc8_14 [symbolic = %Self]
+// CHECK:STDOUT:     %.loc8_14.2: type = converted %Self.ref.loc8_14, %.loc8_14.1 [symbolic = %Self]
+// CHECK:STDOUT:     %self.loc8_8.1: Self = param self
+// CHECK:STDOUT:     %self.loc8_8.2: Self = bind_name self, %self.loc8_8.1
+// CHECK:STDOUT:     %Self.ref.loc8_27: I = name_ref Self, %Self [symbolic = %Self]
+// CHECK:STDOUT:     %.loc8_27.1: type = facet_type_access %Self.ref.loc8_27 [symbolic = %Self]
+// CHECK:STDOUT:     %.loc8_27.2: type = converted %Self.ref.loc8_27, %.loc8_27.1 [symbolic = %Self]
+// CHECK:STDOUT:     %other.loc8_20.1: Self = param other
+// CHECK:STDOUT:     %other.loc8_20.2: Self = bind_name other, %other.loc8_20.1
+// CHECK:STDOUT:     %Self.ref.loc8_36: I = name_ref Self, %Self [symbolic = %Self]
+// CHECK:STDOUT:     %.loc8_36.1: type = facet_type_access %Self.ref.loc8_36 [symbolic = %Self]
+// CHECK:STDOUT:     %.loc8_36.2: type = converted %Self.ref.loc8_36, %.loc8_36.1 [symbolic = %Self]
+// CHECK:STDOUT:     %return.var: ref Self = var <return slot>
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %.loc8_40: <associated <function> in I> = assoc_entity element0, %F [template = constants.%.3]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = %Self
+// CHECK:STDOUT:   .F = %.loc8_40
+// CHECK:STDOUT:   witness = (%F)
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: impl @impl: i32 as I {
+// CHECK:STDOUT:   %F: <function> = fn_decl @F.2 [template] {
+// CHECK:STDOUT:     %self.loc12_8.1: i32 = param self
+// CHECK:STDOUT:     %self.loc12_8.2: i32 = bind_name self, %self.loc12_8.1
+// CHECK:STDOUT:     %other.loc12_19.1: i32 = param other
+// CHECK:STDOUT:     %other.loc12_19.2: i32 = bind_name other, %other.loc12_19.1
+// CHECK:STDOUT:     %return.var: ref i32 = var <return slot>
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %.1: <witness> = interface_witness (%F) [template = constants.%.4]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .F = %F
+// CHECK:STDOUT:   witness = %.1
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @F.1[@I.%self.loc8_8.2: Self](@I.%other.loc8_20.2: Self) -> Self;
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @F.2[@impl.%self.loc12_8.2: i32](@impl.%other.loc12_19.2: i32) -> i32 = "int.add";
+// CHECK:STDOUT:

toolchain/check/testdata/function/call/fail_param_count.carbon

@@ -103,22 +103,22 @@ fn Main() {
 // CHECK:STDOUT: !entry:
 // CHECK:STDOUT:   %Run0.ref.loc18: <function> = name_ref Run0, file.%Run0 [template = file.%Run0]
 // CHECK:STDOUT:   %.loc18_8: i32 = int_literal 1 [template = constants.%.1]
-// CHECK:STDOUT:   %.loc18_7: init () = call %Run0.ref.loc18(<invalid>)
+// CHECK:STDOUT:   %.loc18_7: init () = call %Run0.ref.loc18(<invalid>) [template = <error>]
 // CHECK:STDOUT:   %Run0.ref.loc25: <function> = name_ref Run0, file.%Run0 [template = file.%Run0]
 // CHECK:STDOUT:   %.loc25_8: i32 = int_literal 0 [template = constants.%.3]
 // CHECK:STDOUT:   %.loc25_11: i32 = int_literal 1 [template = constants.%.1]
-// CHECK:STDOUT:   %.loc25_7: init () = call %Run0.ref.loc25(<invalid>)
+// CHECK:STDOUT:   %.loc25_7: init () = call %Run0.ref.loc25(<invalid>) [template = <error>]
 // CHECK:STDOUT:   %Run1.ref.loc33: <function> = name_ref Run1, file.%Run1 [template = file.%Run1]
-// CHECK:STDOUT:   %.loc33: init () = call %Run1.ref.loc33(<invalid>)
+// CHECK:STDOUT:   %.loc33: init () = call %Run1.ref.loc33(<invalid>) [template = <error>]
 // CHECK:STDOUT:   %Run1.ref.loc40: <function> = name_ref Run1, file.%Run1 [template = file.%Run1]
 // CHECK:STDOUT:   %.loc40_8: i32 = int_literal 0 [template = constants.%.3]
 // CHECK:STDOUT:   %.loc40_11: i32 = int_literal 1 [template = constants.%.1]
-// CHECK:STDOUT:   %.loc40_7: init () = call %Run1.ref.loc40(<invalid>)
+// CHECK:STDOUT:   %.loc40_7: init () = call %Run1.ref.loc40(<invalid>) [template = <error>]
 // CHECK:STDOUT:   %Run2.ref.loc48: <function> = name_ref Run2, file.%Run2 [template = file.%Run2]
-// CHECK:STDOUT:   %.loc48: init () = call %Run2.ref.loc48(<invalid>)
+// CHECK:STDOUT:   %.loc48: init () = call %Run2.ref.loc48(<invalid>) [template = <error>]
 // CHECK:STDOUT:   %Run2.ref.loc55: <function> = name_ref Run2, file.%Run2 [template = file.%Run2]
 // CHECK:STDOUT:   %.loc55_8: i32 = int_literal 0 [template = constants.%.3]
-// CHECK:STDOUT:   %.loc55_7: init () = call %Run2.ref.loc55(<invalid>)
+// CHECK:STDOUT:   %.loc55_7: init () = call %Run2.ref.loc55(<invalid>) [template = <error>]
 // CHECK:STDOUT:   return
 // CHECK:STDOUT: }
 // CHECK:STDOUT:

toolchain/check/testdata/function/call/fail_param_type.carbon

@@ -44,7 +44,7 @@ fn F() {
 // CHECK:STDOUT: !entry:
 // CHECK:STDOUT:   %G.ref: <function> = name_ref G, file.%G [template = file.%G]
 // CHECK:STDOUT:   %.loc16_5: f64 = real_literal 10e-1 [template = constants.%.1]
-// CHECK:STDOUT:   %.loc16_4: init () = call %G.ref(<invalid>)
+// CHECK:STDOUT:   %.loc16_4: init () = call %G.ref(<invalid>) [template = <error>]
 // CHECK:STDOUT:   return
 // CHECK:STDOUT: }
 // CHECK:STDOUT: