Commit c1cc1ebc35f7a56669db2f88b6d4ff8f1603ec59 | zig

author	LemonBoy <thatlemon@gmail.com> 2020-03-30 13:27:19+02:00
committer	Andrew Kelley <andrew@ziglang.org> 2020-03-30 11:03:56-04:00
log	c1cc1ebc35f7a56669db2f88b6d4ff8f1603ec59
tree	17e1064c3d862df1bed5ea4f2e73d789afb1893f
parent	8cad45349510b2995a49fc907bdc3c8bf86aa21b

ir: Avoid constant-folding ptr to sentinels

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

2 files changed, 16 insertions(+), 12 deletions(-)

src
- ir.cpp
test
- stage1
  - behavior
    array.zig

src/ir.cpp+2-7

 @@ -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;
+            uint64_t array_len = array_type->data.array.len +
-            if (index == array_len && array_type->data.array.sentinel != nullptr) {
+                (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);
-            }
             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,

test/stage1/behavior/array.zig+14-5

 @@ -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);
         }