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ir: Avoid constant-folding ptr to sentinels

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Constant-folding the pointers to the expected sentinel value have some
big problems: it hides the real content of the array, makes the pointer
to the sentinel point to a completely different memory region and treats
it like a const value even when the underlying array is mutable.

Fixes #4840
This commit is contained in:
LemonBoy 2020-03-30 13:27:19 +02:00 committed by Andrew Kelley
parent 8cad453495
commit c1cc1ebc35
2 changed files with 16 additions and 12 deletions
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9
src/ir.cpp
View File

@ -20880,13 +20880,8 @@ static IrInstGen *ir_analyze_instruction_elem_ptr(IrAnalyze *ira, IrInstSrcElemP
if (instr_is_comptime(casted_elem_index)) {
uint64_t index = bigint_as_u64(&casted_elem_index->value->data.x_bigint);
if (array_type->id == ZigTypeIdArray) {
uint64_t array_len = array_type->data.array.len;
if (index == array_len && array_type->data.array.sentinel != nullptr) {
ZigType *elem_type = array_type->data.array.child_type;
IrInstGen *sentinel_elem = ir_const(ira, &elem_ptr_instruction->base.base, elem_type);
copy_const_val(ira->codegen, sentinel_elem->value, array_type->data.array.sentinel);
return ir_get_ref(ira, &elem_ptr_instruction->base.base, sentinel_elem, true, false);
}
uint64_t array_len = array_type->data.array.len +
(array_type->data.array.sentinel != nullptr);
if (index >= array_len) {
ir_add_error_node(ira, elem_ptr_instruction->base.base.source_node,
buf_sprintf("index %" ZIG_PRI_u64 " outside array of size %" ZIG_PRI_u64,

19
test/stage1/behavior/array.zig
View File

@ -31,14 +31,23 @@ fn getArrayLen(a: []const u32) usize {
test "array with sentinels" {
const S = struct {
fn doTheTest(is_ct: bool) void {
var zero_sized: [0:0xde]u8 = [_:0xde]u8{};
expectEqual(@as(u8, 0xde), zero_sized[0]);
// Disabled at runtime because of
// https://github.com/ziglang/zig/issues/4372
if (is_ct) {
var zero_sized: [0:0xde]u8 = [_:0xde]u8{};
// Disabled at runtime because of
// https://github.com/ziglang/zig/issues/4372
expectEqual(@as(u8, 0xde), zero_sized[0]);
var reinterpreted = @ptrCast(*[1]u8, &zero_sized);
expectEqual(@as(u8, 0xde), reinterpreted[0]);
}
var arr: [3:0x55]u8 = undefined;
// Make sure the sentinel pointer is pointing after the last element
if (!is_ct) {
const sentinel_ptr = @ptrToInt(&arr[3]);
const last_elem_ptr = @ptrToInt(&arr[2]);
expectEqual(@as(usize, 1), sentinel_ptr - last_elem_ptr);
}
// Make sure the sentinel is writeable
arr[3] = 0x55;
}
};
@ -372,7 +381,7 @@ test "access the null element of a null terminated array" {
const S = struct {
fn doTheTest() void {
var array: [4:0]u8 = .{ 'a', 'o', 'e', 'u' };
comptime expect(array[4] == 0);
expect(array[4] == 0);
var len: usize = 4;
expect(array[len] == 0);
}