Fix rejection of arrays with eight or nine elements. (#3199)

In general, LLVM's parsing of decimal integers to `APInt`s forms an
`APInt` that is 4n bits wide, where n is the length of the integer, and
the `isNegative` check only checks the high bit.

In this case, we form an `APInt` that is four bits wide, with the high
bit set, which we reject because we think it's "negative". These two
array lengths are the only ones where this happens -- if the decimal
integer value is two characters long, we form an `APInt` that is eight
bits wide but holds a value < 100, so the high bit is never set, and the
same applies for longer integers too.

An `IntegerLiteral` is never negative, so we don't need the `isNegative`
check, and in fact it only detects the n=8 and n=9 cases.

toolchain/check/handle_array.cpp

@@ -37,7 +37,8 @@ auto HandleArrayExpression(Context& context, Parse::Node parse_node) -> bool {
   if (bound_node.kind() == SemIR::NodeKind::IntegerLiteral) {
     auto bound_value = context.semantics_ir().GetIntegerLiteral(
         bound_node.GetAsIntegerLiteral());
-    if (!bound_value.isNegative() && bound_value.getBitWidth() <= 64) {
+    // TODO: Produce an error if the array type is too large.
+    if (bound_value.getBitWidth() <= 64) {
       context.AddNodeAndPush(
           parse_node,
           SemIR::Node::ArrayType::Make(

toolchain/check/testdata/array/nine_elements.carbon

@@ -0,0 +1,143 @@
+// 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
+
+var a: [i32; 9] = (1, 2, 3, 4, 5, 6, 7, 8, 9);
+
+// CHECK:STDOUT: cross_reference_irs_size: 1
+// CHECK:STDOUT: functions: [
+// CHECK:STDOUT: ]
+// CHECK:STDOUT: integer_literals: [
+// CHECK:STDOUT:   -7,
+// CHECK:STDOUT:   1,
+// CHECK:STDOUT:   2,
+// CHECK:STDOUT:   3,
+// CHECK:STDOUT:   4,
+// CHECK:STDOUT:   5,
+// CHECK:STDOUT:   6,
+// CHECK:STDOUT:   7,
+// CHECK:STDOUT:   -8,
+// CHECK:STDOUT:   -7,
+// CHECK:STDOUT: ]
+// CHECK:STDOUT: real_literals: [
+// CHECK:STDOUT: ]
+// CHECK:STDOUT: strings: [
+// CHECK:STDOUT:   a,
+// CHECK:STDOUT: ]
+// CHECK:STDOUT: types: [
+// CHECK:STDOUT:   nodeIntegerType,
+// CHECK:STDOUT:   node+1,
+// CHECK:STDOUT:   node+21,
+// CHECK:STDOUT: ]
+// CHECK:STDOUT: type_blocks: [
+// CHECK:STDOUT:   [
+// CHECK:STDOUT:     type0,
+// CHECK:STDOUT:     type0,
+// CHECK:STDOUT:     type0,
+// CHECK:STDOUT:     type0,
+// CHECK:STDOUT:     type0,
+// CHECK:STDOUT:     type0,
+// CHECK:STDOUT:     type0,
+// CHECK:STDOUT:     type0,
+// CHECK:STDOUT:     type0,
+// CHECK:STDOUT:   ],
+// CHECK:STDOUT: ]
+// CHECK:STDOUT: nodes: [
+// CHECK:STDOUT:   {kind: IntegerLiteral, arg0: int0, type: type0},
+// CHECK:STDOUT:   {kind: ArrayType, arg0: node+0, arg1: type0, type: typeTypeType},
+// CHECK:STDOUT:   {kind: VarStorage, arg0: str0, type: type1},
+// CHECK:STDOUT:   {kind: IntegerLiteral, arg0: int1, type: type0},
+// CHECK:STDOUT:   {kind: StubReference, arg0: node+3, type: type0},
+// CHECK:STDOUT:   {kind: IntegerLiteral, arg0: int2, type: type0},
+// CHECK:STDOUT:   {kind: StubReference, arg0: node+5, type: type0},
+// CHECK:STDOUT:   {kind: IntegerLiteral, arg0: int3, type: type0},
+// CHECK:STDOUT:   {kind: StubReference, arg0: node+7, type: type0},
+// CHECK:STDOUT:   {kind: IntegerLiteral, arg0: int4, type: type0},
+// CHECK:STDOUT:   {kind: StubReference, arg0: node+9, type: type0},
+// CHECK:STDOUT:   {kind: IntegerLiteral, arg0: int5, type: type0},
+// CHECK:STDOUT:   {kind: StubReference, arg0: node+11, type: type0},
+// CHECK:STDOUT:   {kind: IntegerLiteral, arg0: int6, type: type0},
+// CHECK:STDOUT:   {kind: StubReference, arg0: node+13, type: type0},
+// CHECK:STDOUT:   {kind: IntegerLiteral, arg0: int7, type: type0},
+// CHECK:STDOUT:   {kind: StubReference, arg0: node+15, type: type0},
+// CHECK:STDOUT:   {kind: IntegerLiteral, arg0: int8, type: type0},
+// CHECK:STDOUT:   {kind: StubReference, arg0: node+17, type: type0},
+// CHECK:STDOUT:   {kind: IntegerLiteral, arg0: int9, type: type0},
+// CHECK:STDOUT:   {kind: StubReference, arg0: node+19, type: type0},
+// CHECK:STDOUT:   {kind: TupleType, arg0: typeBlock0, type: typeTypeType},
+// CHECK:STDOUT:   {kind: TupleValue, arg0: block2, type: type2},
+// CHECK:STDOUT:   {kind: ArrayValue, arg0: node+22, type: type1},
+// CHECK:STDOUT:   {kind: Assign, arg0: node+2, arg1: node+23},
+// CHECK:STDOUT: ]
+// CHECK:STDOUT: node_blocks: [
+// CHECK:STDOUT:   [
+// CHECK:STDOUT:   ],
+// CHECK:STDOUT:   [
+// CHECK:STDOUT:     node+0,
+// CHECK:STDOUT:     node+1,
+// CHECK:STDOUT:     node+2,
+// CHECK:STDOUT:     node+3,
+// CHECK:STDOUT:     node+4,
+// CHECK:STDOUT:     node+5,
+// CHECK:STDOUT:     node+6,
+// CHECK:STDOUT:     node+7,
+// CHECK:STDOUT:     node+8,
+// CHECK:STDOUT:     node+9,
+// CHECK:STDOUT:     node+10,
+// CHECK:STDOUT:     node+11,
+// CHECK:STDOUT:     node+12,
+// CHECK:STDOUT:     node+13,
+// CHECK:STDOUT:     node+14,
+// CHECK:STDOUT:     node+15,
+// CHECK:STDOUT:     node+16,
+// CHECK:STDOUT:     node+17,
+// CHECK:STDOUT:     node+18,
+// CHECK:STDOUT:     node+19,
+// CHECK:STDOUT:     node+20,
+// CHECK:STDOUT:     node+21,
+// CHECK:STDOUT:     node+22,
+// CHECK:STDOUT:     node+23,
+// CHECK:STDOUT:     node+24,
+// CHECK:STDOUT:   ],
+// CHECK:STDOUT:   [
+// CHECK:STDOUT:     node+4,
+// CHECK:STDOUT:     node+6,
+// CHECK:STDOUT:     node+8,
+// CHECK:STDOUT:     node+10,
+// CHECK:STDOUT:     node+12,
+// CHECK:STDOUT:     node+14,
+// CHECK:STDOUT:     node+16,
+// CHECK:STDOUT:     node+18,
+// CHECK:STDOUT:     node+20,
+// CHECK:STDOUT:   ],
+// CHECK:STDOUT: ]
+// CHECK:STDOUT:
+// CHECK:STDOUT: package {
+// CHECK:STDOUT:   %.loc7_14: i32 = int_literal -7
+// CHECK:STDOUT:   %.loc7_15: type = array_type %.loc7_14, i32
+// CHECK:STDOUT:   %a: ref [i32; 9] = var "a"
+// CHECK:STDOUT:   %.loc7_20.1: i32 = int_literal 1
+// CHECK:STDOUT:   %.loc7_20.2: i32 = stub_reference %.loc7_20.1
+// CHECK:STDOUT:   %.loc7_23.1: i32 = int_literal 2
+// CHECK:STDOUT:   %.loc7_23.2: i32 = stub_reference %.loc7_23.1
+// CHECK:STDOUT:   %.loc7_26.1: i32 = int_literal 3
+// CHECK:STDOUT:   %.loc7_26.2: i32 = stub_reference %.loc7_26.1
+// CHECK:STDOUT:   %.loc7_29.1: i32 = int_literal 4
+// CHECK:STDOUT:   %.loc7_29.2: i32 = stub_reference %.loc7_29.1
+// CHECK:STDOUT:   %.loc7_32.1: i32 = int_literal 5
+// CHECK:STDOUT:   %.loc7_32.2: i32 = stub_reference %.loc7_32.1
+// CHECK:STDOUT:   %.loc7_35.1: i32 = int_literal 6
+// CHECK:STDOUT:   %.loc7_35.2: i32 = stub_reference %.loc7_35.1
+// CHECK:STDOUT:   %.loc7_38.1: i32 = int_literal 7
+// CHECK:STDOUT:   %.loc7_38.2: i32 = stub_reference %.loc7_38.1
+// CHECK:STDOUT:   %.loc7_41.1: i32 = int_literal -8
+// CHECK:STDOUT:   %.loc7_41.2: i32 = stub_reference %.loc7_41.1
+// CHECK:STDOUT:   %.loc7_44.1: i32 = int_literal -7
+// CHECK:STDOUT:   %.loc7_44.2: i32 = stub_reference %.loc7_44.1
+// CHECK:STDOUT:   %.loc7_45.1: type = tuple_type (i32, i32, i32, i32, i32, i32, i32, i32, i32)
+// CHECK:STDOUT:   %.loc7_45.2: (i32, i32, i32, i32, i32, i32, i32, i32, i32) = tuple_value (%.loc7_20.2, %.loc7_23.2, %.loc7_26.2, %.loc7_29.2, %.loc7_32.2, %.loc7_35.2, %.loc7_38.2, %.loc7_41.2, %.loc7_44.2)
+// CHECK:STDOUT:   %.loc7_45.3: [i32; 9] = array_value %.loc7_45.2
+// CHECK:STDOUT:   assign %a, %.loc7_45.3
+// CHECK:STDOUT: }