Commit `5374e245c5`

Cody Tapscott <topolarity@tapscott.me>

2022-03-23 07:32:57

stage2: Remove premature elem_val index check

We were enforcing bounds on the index of an elem_ptr in pointerDeref, but we want to support out-of-bounds accesses by reinterpreting memory. This removes that check, so that the deref falls back to bitcasting, as usual. This was masked by another bug that was forcing bitcasts incorrectly, which is why this wasn't noticed earlier.

master

1 parent 1c22381

Changed files (1)

src

Sema.zig

@@ -18752,6 +18752,11 @@ fn beginComptimePtrLoad(
             const elem_ty = elem_ptr.elem_ty;
             var deref = try beginComptimePtrLoad(sema, block, src, elem_ptr.array_ptr, null);
 
+            // This code assumes that elem_ptrs have been "flattened" in order for direct dereference
+            // to succeed, meaning that elem ptrs of the same elem_ty are coalesced. Here we check that
+            // our parent is not an elem_ptr with the same elem_ty, since that would be "unflattened"
+            if (elem_ptr.array_ptr.castTag(.elem_ptr)) |parent_elem_ptr| assert(!(parent_elem_ptr.data.elem_ty.eql(elem_ty, target)));
+
             if (elem_ptr.index != 0) {
                 if (elem_ty.hasWellDefinedLayout()) {
                     if (deref.parent) |*parent| {
@@ -18780,13 +18785,6 @@ fn beginComptimePtrLoad(
 
             var array_tv = deref.pointee.?;
             const check_len = array_tv.ty.arrayLenIncludingSentinel();
-            if (elem_ptr.index >= check_len) {
-                // TODO have the deref include the decl so we can say "declared here"
-                return sema.fail(block, src, "comptime load of index {d} out of bounds of array length {d}", .{
-                    elem_ptr.index, check_len,
-                });
-            }
-
             if (maybe_array_ty) |load_ty| {
                 // It's possible that we're loading a [N]T, in which case we'd like to slice
                 // the pointee array directly from our parent array.
@@ -18800,10 +18798,10 @@ fn beginComptimePtrLoad(
                 }
             }
 
-            deref.pointee = .{
+            deref.pointee = if (elem_ptr.index < check_len) TypedValue{
                 .ty = elem_ty,
                 .val = try array_tv.val.elemValue(sema.arena, elem_ptr.index),
-            };
+            } else null;
             break :blk deref;
         },

Commit 5374e245c5

Commit `5374e245c5`