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frontend: vectors and arrays no longer support in-memory coercion

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closes #25172
This commit is contained in:
Andrew Kelley 2025-09-07 17:28:01 -07:00
parent 426d65d700
commit 6673b47685
3 changed files with 9 additions and 45 deletions
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8
doc/langref.html.in
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@ -1969,6 +1969,14 @@ or
</p>
{#see_also|@splat|@shuffle|@select|@reduce#}
{#header_open|Relationship with Arrays#}
<p>Vectors and {#link|Arrays#} each have a well-defined <strong>bit layout</strong>
and therefore support {#link|@bitCast#} between each other. {#link|Type Coercion#} implicitly peforms
{#syntax#}@bitCast{#endsyntax#}.</p>
<p>Arrays have well-defined byte layout, but vectors do not, making {#link|@ptrCast#} between
them {#link|Illegal Behavior#}.</p>
{#header_close#}
{#header_open|Destructuring Vectors#}
<p>
Vectors can be destructured:

2
doc/langref/test_vector.zig
View file

@ -17,7 +17,7 @@ test "Basic vector usage" {
}
test "Conversion between vectors, arrays, and slices" {
// Vectors and fixed-length arrays can be automatically assigned back and forth
// Vectors can be coerced to arrays, and vice versa.
const arr1: [4]f32 = [_]f32{ 1.1, 3.2, 4.5, 5.6 };
const vec: @Vector(4, f32) = arr1;
const arr2: [4]f32 = vec;

44
src/Sema.zig
View file

@ -29649,50 +29649,6 @@ pub fn coerceInMemoryAllowed(
return .ok;
}
// Arrays <-> Vectors
if ((dest_tag == .vector and src_tag == .array) or
(dest_tag == .array and src_tag == .vector))
{
const dest_len = dest_ty.arrayLen(zcu);
const src_len = src_ty.arrayLen(zcu);
if (dest_len != src_len) {
return .{ .array_len = .{
.actual = src_len,
.wanted = dest_len,
} };
}
const dest_elem_ty = dest_ty.childType(zcu);
const src_elem_ty = src_ty.childType(zcu);
const child = try sema.coerceInMemoryAllowed(block, dest_elem_ty, src_elem_ty, dest_is_mut, target, dest_src, src_src, null);
if (child != .ok) {
return .{ .array_elem = .{
.child = try child.dupe(sema.arena),
.actual = src_elem_ty,
.wanted = dest_elem_ty,
} };
}
if (dest_tag == .array) {
const dest_info = dest_ty.arrayInfo(zcu);
if (dest_info.sentinel != null) {
return .{ .array_sentinel = .{
.actual = Value.@"unreachable",
.wanted = dest_info.sentinel.?,
.ty = dest_info.elem_type,
} };
}
}
// The memory layout of @Vector(N, iM) is the same as the integer type i(N*M),
// that is to say, the padding bits are not in the same place as the array [N]iM.
// If there's no padding, the bitcast is possible.
const elem_bit_size = dest_elem_ty.bitSize(zcu);
const elem_abi_byte_size = dest_elem_ty.abiSize(zcu);
if (elem_abi_byte_size * 8 == elem_bit_size)
return .ok;
}
// Optionals
if (dest_tag == .optional and src_tag == .optional) {
if ((maybe_dest_ptr_ty != null) != (maybe_src_ptr_ty != null)) {