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Sema: correct AIR semantics around array concat optimization #25594

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114 changes: 75 additions & 39 deletions src/Sema.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -14562,8 +14562,9 @@ fn zirArrayCat(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Ai

const mutable_alloc = try block.addTy(.alloc, alloc_ty);

// if both the source and destination are arrays
// we can hotpath via a memcpy.
// there's nothing to copy
if (result_len == 0 and res_sent_val == null) return mutable_alloc;

if (lhs_ty.zigTypeTag(zcu) == .pointer and
rhs_ty.zigTypeTag(zcu) == .pointer)
{
Expand All @@ -14576,48 +14577,83 @@ fn zirArrayCat(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Ai
});

const many_ty = slice_ty.slicePtrFieldType(zcu);
const many_alloc = try block.addBitCast(many_ty, mutable_alloc);
const many_ty_ref = Air.internedToRef(many_ty.toIntern());

// lhs_dest_slice = dest[0..lhs.len]
const slice_ty_ref = Air.internedToRef(slice_ty.toIntern());
const lhs_len_ref = try pt.intRef(.usize, lhs_len);
const lhs_dest_slice = try block.addInst(.{
.tag = .slice,
.data = .{ .ty_pl = .{
.ty = slice_ty_ref,
.payload = try sema.addExtra(Air.Bin{
.lhs = many_alloc,
.rhs = lhs_len_ref,
}),
} },
});

_ = try block.addBinOp(.memcpy, lhs_dest_slice, lhs);
// @memcpy(@as(*[lhs.len]T, dst[0..lhs.len]), lhs.ptr)
if (lhs_len != 0) {
const lhs_dest_slice = switch (rhs_len) {
0 => mutable_alloc,
else => s: {
// [lhs.len]T
const array_ty = try pt.arrayType(.{
.child = resolved_elem_ty.toIntern(),
.len = lhs_len,
});
// *[lhs.len]T
const mutable_ty = try pt.ptrTypeSema(.{
.child = array_ty.toIntern(),
.flags = .{ .address_space = ptr_as },
});
break :s try block.addBitCast(mutable_ty, mutable_alloc);
},
};
const lhs_src_pointer = if (lhs_ty.isSlice(zcu))
try block.addInst(.{
.tag = .slice_ptr,
.data = .{ .ty_op = .{
.ty = many_ty_ref,
.operand = lhs,
} },
})
else
lhs;
_ = try block.addBinOp(.memcpy, lhs_dest_slice, lhs_src_pointer);
}

if (rhs_len != 0) {
const rhs_dest_slice = switch (lhs_len) {
0 => mutable_alloc,
else => s: {
const many_alloc = try block.addBitCast(many_ty, mutable_alloc);
const rhs_dest_offset = try block.addInst(.{
.tag = .ptr_add,
.data = .{ .ty_pl = .{
.ty = many_ty_ref,
.payload = try sema.addExtra(Air.Bin{
.lhs = many_alloc,
.rhs = lhs_len_ref,
}),
} },
});

// rhs_dest_slice = dest[lhs.len..][0..rhs.len]
const rhs_len_ref = try pt.intRef(.usize, rhs_len);
const rhs_dest_offset = try block.addInst(.{
.tag = .ptr_add,
.data = .{ .ty_pl = .{
.ty = Air.internedToRef(many_ty.toIntern()),
.payload = try sema.addExtra(Air.Bin{
.lhs = many_alloc,
.rhs = lhs_len_ref,
}),
} },
});
const rhs_dest_slice = try block.addInst(.{
.tag = .slice,
.data = .{ .ty_pl = .{
.ty = slice_ty_ref,
.payload = try sema.addExtra(Air.Bin{
.lhs = rhs_dest_offset,
.rhs = rhs_len_ref,
}),
} },
});
// [rhs.len]T
const array_ty = try pt.arrayType(.{
.child = resolved_elem_ty.toIntern(),
.len = lhs_len,
});
// *[rhs.len]T
const mutable_ty = try pt.ptrTypeSema(.{
.child = array_ty.toIntern(),
.flags = .{ .address_space = ptr_as },
});

_ = try block.addBinOp(.memcpy, rhs_dest_slice, rhs);
break :s try block.addBitCast(mutable_ty, rhs_dest_offset);
},
};
const rhs_src_pointer = if (rhs_ty.isSlice(zcu))
try block.addInst(.{
.tag = .slice_ptr,
.data = .{ .ty_op = .{
.ty = many_ty_ref,
.operand = rhs,
} },
})
else
rhs;
_ = try block.addBinOp(.memcpy, rhs_dest_slice, rhs_src_pointer);
}

if (res_sent_val) |sent_val| {
const elem_index = try pt.intRef(.usize, result_len);
Expand Down
6 changes: 6 additions & 0 deletions test/behavior/array.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -92,6 +92,12 @@ test "array init with concat" {
try expect(std.mem.eql(u8, &i, "abcd"));
}

test "array concat zero length pointers" {
var x: *const [0]u8 = &.{};
_ = &x;
_ = @as([]const u8, "") ++ x;
}

test "array init with mult" {
if (builtin.zig_backend == .stage2_spirv) return error.SkipZigTest;
if (builtin.zig_backend == .stage2_sparc64) return error.SkipZigTest; // TODO
Expand Down
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