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Sema: support pointer subtraction

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Wooster 2024-07-16 03:18:38 +09:00 • committed by GitHub
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7 changed files with 230 additions and 46 deletions
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9
doc/langref.html.in
View file

@ -1935,16 +1935,18 @@ or
<li>{#syntax#}*T{#endsyntax#} - single-item pointer to exactly one item.
<ul>
<li>Supports deref syntax: {#syntax#}ptr.*{#endsyntax#}</li>
<li>Supports pointer subtraction: {#syntax#}ptr - ptr{#endsyntax#}</li>
</ul>
</li>
<li>{#syntax#}[*]T{#endsyntax#} - many-item pointer to unknown number of items.
<ul>
<li>Supports index syntax: {#syntax#}ptr[i]{#endsyntax#}</li>
<li>Supports slice syntax: {#syntax#}ptr[start..end]{#endsyntax#} and {#syntax#}ptr[start..]{#endsyntax#}</li>
<li>Supports pointer arithmetic: {#syntax#}ptr + x{#endsyntax#}, {#syntax#}ptr - x{#endsyntax#}</li>
<li>{#syntax#}T{#endsyntax#} must have a known size, which means that it cannot be
{#syntax#}anyopaque{#endsyntax#} or any other {#link|opaque type|opaque#}.</li>
<li>Supports pointer-integer arithmetic: {#syntax#}ptr + int{#endsyntax#}, {#syntax#}ptr - int{#endsyntax#}</li>
<li>Supports pointer subtraction: {#syntax#}ptr - ptr{#endsyntax#}</li>
</ul>
{#syntax#}T{#endsyntax#} must have a known size, which means that it cannot be
{#syntax#}anyopaque{#endsyntax#} or any other {#link|opaque type|opaque#}.
</li>
</ul>
<p>These types are closely related to {#link|Arrays#} and {#link|Slices#}:</p>
@ -1954,6 +1956,7 @@ or
<li>Supports index syntax: {#syntax#}array_ptr[i]{#endsyntax#}</li>
<li>Supports slice syntax: {#syntax#}array_ptr[start..end]{#endsyntax#}</li>
<li>Supports len property: {#syntax#}array_ptr.len{#endsyntax#}</li>
<li>Supports pointer subtraction: {#syntax#}array_ptr - array_ptr{#endsyntax#}</li>
</ul>
</li>
</ul>

3
doc/langref/test_pointer_arithmetic.zig
View file

@ -11,6 +11,9 @@ test "pointer arithmetic with many-item pointer" {
// slicing a many-item pointer without an end is equivalent to
// pointer arithmetic: `ptr[start..] == ptr + start`
try expect(ptr[1..] == ptr + 1);
// subtraction between any two pointers except slices based on element size is supported
try expect(&ptr[1] - &ptr[0] == 1);
}
test "pointer arithmetic with slices" {

34
src/InternPool.zig
View file

@ -1931,6 +1931,23 @@ pub const Key = union(enum) {
/// the original pointer type alignment must be used.
orig_ty: Index,
};
pub fn eql(a: BaseAddr, b: BaseAddr) bool {
if (@as(Key.Ptr.BaseAddr.Tag, a) != @as(Key.Ptr.BaseAddr.Tag, b)) return false;
return switch (a) {
.decl => |a_decl| a_decl == b.decl,
.comptime_alloc => |a_alloc| a_alloc == b.comptime_alloc,
.anon_decl => |ad| ad.val == b.anon_decl.val and
ad.orig_ty == b.anon_decl.orig_ty,
.int => true,
.eu_payload => |a_eu_payload| a_eu_payload == b.eu_payload,
.opt_payload => |a_opt_payload| a_opt_payload == b.opt_payload,
.comptime_field => |a_comptime_field| a_comptime_field == b.comptime_field,
.arr_elem => |a_elem| std.meta.eql(a_elem, b.arr_elem),
.field => |a_field| std.meta.eql(a_field, b.field),
};
}
};
};
@ -2369,21 +2386,8 @@ pub const Key = union(enum) {
const b_info = b.ptr;
if (a_info.ty != b_info.ty) return false;
if (a_info.byte_offset != b_info.byte_offset) return false;
if (@as(Key.Ptr.BaseAddr.Tag, a_info.base_addr) != @as(Key.Ptr.BaseAddr.Tag, b_info.base_addr)) return false;
return switch (a_info.base_addr) {
.decl => |a_decl| a_decl == b_info.base_addr.decl,
.comptime_alloc => |a_alloc| a_alloc == b_info.base_addr.comptime_alloc,
.anon_decl => |ad| ad.val == b_info.base_addr.anon_decl.val and
ad.orig_ty == b_info.base_addr.anon_decl.orig_ty,
.int => true,
.eu_payload => |a_eu_payload| a_eu_payload == b_info.base_addr.eu_payload,
.opt_payload => |a_opt_payload| a_opt_payload == b_info.base_addr.opt_payload,
.comptime_field => |a_comptime_field| a_comptime_field == b_info.base_addr.comptime_field,
.arr_elem => |a_elem| std.meta.eql(a_elem, b_info.base_addr.arr_elem),
.field => |a_field| std.meta.eql(a_field, b_info.base_addr.field),
};
if (!a_info.base_addr.eql(b_info.base_addr)) return false;
return true;
},
.int => |a_info| {

116
src/Sema.zig
View file

@ -2429,6 +2429,16 @@ fn failWithComptimeErrorRetTrace(
return sema.failWithOwnedErrorMsg(block, msg);
}
fn failWithInvalidPtrArithmetic(sema: *Sema, block: *Block, src: LazySrcLoc, arithmetic: []const u8, supports: []const u8) CompileError {
const msg = msg: {
const msg = try sema.errMsg(src, "invalid {s} arithmetic operator", .{arithmetic});
errdefer msg.destroy(sema.gpa);
try sema.errNote(src, msg, "{s} arithmetic only supports {s}", .{ arithmetic, supports });
break :msg msg;
};
return sema.failWithOwnedErrorMsg(block, msg);
}
/// We don't return a pointer to the new error note because the pointer
/// becomes invalid when you add another one.
pub fn errNote(
@ -15146,7 +15156,7 @@ fn zirDiv(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Ins
const lhs_zig_ty_tag = try lhs_ty.zigTypeTagOrPoison(mod);
const rhs_zig_ty_tag = try rhs_ty.zigTypeTagOrPoison(mod);
try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
try sema.checkInvalidPtrArithmetic(block, src, lhs_ty);
try sema.checkInvalidPtrIntArithmetic(block, src, lhs_ty);
const instructions = &[_]Air.Inst.Ref{ lhs, rhs };
const resolved_type = try sema.resolvePeerTypes(block, src, instructions, .{
@ -15312,7 +15322,7 @@ fn zirDivExact(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Ai
const lhs_zig_ty_tag = try lhs_ty.zigTypeTagOrPoison(mod);
const rhs_zig_ty_tag = try rhs_ty.zigTypeTagOrPoison(mod);
try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
try sema.checkInvalidPtrArithmetic(block, src, lhs_ty);
try sema.checkInvalidPtrIntArithmetic(block, src, lhs_ty);
const instructions = &[_]Air.Inst.Ref{ lhs, rhs };
const resolved_type = try sema.resolvePeerTypes(block, src, instructions, .{
@ -15478,7 +15488,7 @@ fn zirDivFloor(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Ai
const lhs_zig_ty_tag = try lhs_ty.zigTypeTagOrPoison(mod);
const rhs_zig_ty_tag = try rhs_ty.zigTypeTagOrPoison(mod);
try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
try sema.checkInvalidPtrArithmetic(block, src, lhs_ty);
try sema.checkInvalidPtrIntArithmetic(block, src, lhs_ty);
const instructions = &[_]Air.Inst.Ref{ lhs, rhs };
const resolved_type = try sema.resolvePeerTypes(block, src, instructions, .{
@ -15589,7 +15599,7 @@ fn zirDivTrunc(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Ai
const lhs_zig_ty_tag = try lhs_ty.zigTypeTagOrPoison(mod);
const rhs_zig_ty_tag = try rhs_ty.zigTypeTagOrPoison(mod);
try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
try sema.checkInvalidPtrArithmetic(block, src, lhs_ty);
try sema.checkInvalidPtrIntArithmetic(block, src, lhs_ty);
const instructions = &[_]Air.Inst.Ref{ lhs, rhs };
const resolved_type = try sema.resolvePeerTypes(block, src, instructions, .{
@ -15833,7 +15843,7 @@ fn zirModRem(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.
const lhs_zig_ty_tag = try lhs_ty.zigTypeTagOrPoison(mod);
const rhs_zig_ty_tag = try rhs_ty.zigTypeTagOrPoison(mod);
try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
try sema.checkInvalidPtrArithmetic(block, src, lhs_ty);
try sema.checkInvalidPtrIntArithmetic(block, src, lhs_ty);
const instructions = &[_]Air.Inst.Ref{ lhs, rhs };
const resolved_type = try sema.resolvePeerTypes(block, src, instructions, .{
@ -16019,7 +16029,7 @@ fn zirMod(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Ins
const lhs_zig_ty_tag = try lhs_ty.zigTypeTagOrPoison(mod);
const rhs_zig_ty_tag = try rhs_ty.zigTypeTagOrPoison(mod);
try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
try sema.checkInvalidPtrArithmetic(block, src, lhs_ty);
try sema.checkInvalidPtrIntArithmetic(block, src, lhs_ty);
const instructions = &[_]Air.Inst.Ref{ lhs, rhs };
const resolved_type = try sema.resolvePeerTypes(block, src, instructions, .{
@ -16115,7 +16125,7 @@ fn zirRem(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Ins
const lhs_zig_ty_tag = try lhs_ty.zigTypeTagOrPoison(mod);
const rhs_zig_ty_tag = try rhs_ty.zigTypeTagOrPoison(mod);
try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
try sema.checkInvalidPtrArithmetic(block, src, lhs_ty);
try sema.checkInvalidPtrIntArithmetic(block, src, lhs_ty);
const instructions = &[_]Air.Inst.Ref{ lhs, rhs };
const resolved_type = try sema.resolvePeerTypes(block, src, instructions, .{
@ -16458,17 +16468,78 @@ fn analyzeArithmetic(
const rhs_zig_ty_tag = try rhs_ty.zigTypeTagOrPoison(mod);
try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
if (lhs_zig_ty_tag == .Pointer) switch (lhs_ty.ptrSize(mod)) {
.One, .Slice => {},
.Many, .C => {
const air_tag: Air.Inst.Tag = switch (zir_tag) {
.add => .ptr_add,
.sub => .ptr_sub,
else => return sema.fail(block, src, "invalid pointer arithmetic operator", .{}),
};
return sema.analyzePtrArithmetic(block, src, lhs, rhs, air_tag, lhs_src, rhs_src);
},
};
if (lhs_zig_ty_tag == .Pointer) {
if (rhs_zig_ty_tag == .Pointer) {
if (lhs_ty.ptrSize(mod) != .Slice and rhs_ty.ptrSize(mod) != .Slice) {
if (zir_tag != .sub) {
return sema.failWithInvalidPtrArithmetic(block, src, "pointer-pointer", "subtraction");
}
if (!lhs_ty.elemType2(mod).eql(rhs_ty.elemType2(mod), mod)) {
return sema.fail(block, src, "incompatible pointer arithmetic operands '{}' and '{}'", .{
lhs_ty.fmt(pt), rhs_ty.fmt(pt),
});
}
const elem_size = lhs_ty.elemType2(mod).abiSize(pt);
if (elem_size == 0) {
return sema.fail(block, src, "pointer arithmetic requires element type '{}' to have runtime bits", .{
lhs_ty.elemType2(mod).fmt(pt),
});
}
const runtime_src = runtime_src: {
if (try sema.resolveValue(lhs)) |lhs_value| {
if (try sema.resolveValue(rhs)) |rhs_value| {
const lhs_ptr = switch (mod.intern_pool.indexToKey(lhs_value.toIntern())) {
.undef => return sema.failWithUseOfUndef(block, lhs_src),
.ptr => |ptr| ptr,
else => unreachable,
};
const rhs_ptr = switch (mod.intern_pool.indexToKey(rhs_value.toIntern())) {
.undef => return sema.failWithUseOfUndef(block, rhs_src),
.ptr => |ptr| ptr,
else => unreachable,
};
// Make sure the pointers point to the same data.
if (!lhs_ptr.base_addr.eql(rhs_ptr.base_addr)) break :runtime_src src;
const address = std.math.sub(u64, lhs_ptr.byte_offset, rhs_ptr.byte_offset) catch
return sema.fail(block, src, "operation results in overflow", .{});
const result = address / elem_size;
return try pt.intRef(Type.usize, result);
} else {
break :runtime_src lhs_src;
}
} else {
break :runtime_src rhs_src;
}
};
try sema.requireRuntimeBlock(block, src, runtime_src);
const lhs_int = try block.addUnOp(.int_from_ptr, lhs);
const rhs_int = try block.addUnOp(.int_from_ptr, rhs);
const address = try block.addBinOp(.sub_wrap, lhs_int, rhs_int);
return try block.addBinOp(.div_exact, address, try pt.intRef(Type.usize, elem_size));
}
} else {
switch (lhs_ty.ptrSize(mod)) {
.One, .Slice => {},
.Many, .C => {
const air_tag: Air.Inst.Tag = switch (zir_tag) {
.add => .ptr_add,
.sub => .ptr_sub,
else => return sema.failWithInvalidPtrArithmetic(block, src, "pointer-integer", "addition and subtraction"),
};
if (!try sema.typeHasRuntimeBits(lhs_ty.elemType2(mod))) {
return sema.fail(block, src, "pointer arithmetic requires element type '{}' to have runtime bits", .{
lhs_ty.elemType2(mod).fmt(pt),
});
}
return sema.analyzePtrArithmetic(block, src, lhs, rhs, air_tag, lhs_src, rhs_src);
},
}
}
}
const instructions = &[_]Air.Inst.Ref{ lhs, rhs };
const resolved_type = try sema.resolvePeerTypes(block, src, instructions, .{
@ -23762,7 +23833,7 @@ fn checkIntType(sema: *Sema, block: *Block, src: LazySrcLoc, ty: Type) CompileEr
}
}
fn checkInvalidPtrArithmetic(
fn checkInvalidPtrIntArithmetic(
sema: *Sema,
block: *Block,
src: LazySrcLoc,
@ -23773,12 +23844,7 @@ fn checkInvalidPtrArithmetic(
switch (try ty.zigTypeTagOrPoison(mod)) {
.Pointer => switch (ty.ptrSize(mod)) {
.One, .Slice => return,
.Many, .C => return sema.fail(
block,
src,
"invalid pointer arithmetic operator",
.{},
),
.Many, .C => return sema.failWithInvalidPtrArithmetic(block, src, "pointer-integer", "addition and subtraction"),
},
else => return,
}

2
src/Value.zig
View file

@ -3752,7 +3752,7 @@ pub fn ptrField(parent_ptr: Value, field_idx: u32, pt: Zcu.PerThread) !Value {
const parent_ptr_info = parent_ptr_ty.ptrInfo(zcu);
assert(parent_ptr_info.flags.size == .One);
// Exiting this `switch` indicates that the `field` pointer repsentation should be used.
// Exiting this `switch` indicates that the `field` pointer representation should be used.
// `field_align` may be `.none` to represent the natural alignment of `field_ty`, but is not necessarily.
const field_ty: Type, const field_align: InternPool.Alignment = switch (aggregate_ty.zigTypeTag(zcu)) {
.Struct => field: {

60
test/behavior/pointers.zig
View file

@ -17,7 +17,7 @@ fn testDerefPtr() !void {
try expect(x == 1235);
}
test "pointer arithmetic" {
test "pointer-integer arithmetic" {
if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest;
if (builtin.zig_backend == .stage2_sparc64) return error.SkipZigTest; // TODO
if (builtin.zig_backend == .stage2_riscv64) return error.SkipZigTest;
@ -43,6 +43,62 @@ test "pointer arithmetic" {
try expect(ptr[0] == 'a');
}
test "pointer subtraction" {
if (builtin.zig_backend == .stage2_sparc64) return error.SkipZigTest; // TODO
if (builtin.zig_backend == .stage2_riscv64) return error.SkipZigTest;
{
const a: *u8 = @ptrFromInt(100);
const b: *u8 = @ptrFromInt(50);
try expect(a - b == 50);
}
{
var ptr: [*]const u8 = "abc";
try expect(&ptr[1] - &ptr[0] == 1);
try expect(&ptr[2] - &ptr[0] == 2);
}
{
const a: *[100]u16 = @ptrFromInt(100);
const b: *[100]u16 = @ptrFromInt(50);
try expect(a - b == 25);
}
{
var x: struct { a: u32, b: u32 } = undefined;
const a = &x.a;
const b = &x.b;
try expect(a - a == 0);
try expect(b - b == 0);
try expect(b - a == 1);
}
comptime {
var x: packed struct { a: u1, b: u1 } = undefined;
const a = &x.a;
const b = &x.b;
try expect(a - a == 0);
try expect(b - b == 0);
try expect(b - a == 0);
}
comptime {
var x: extern struct { a: u32, b: u32 } = undefined;
const a = &x.a;
const b = &x.b;
try expect(a - a == 0);
try expect(b - b == 0);
try expect(b - a == 1);
}
comptime {
const a: *const [3]u8 = "abc";
const b: [*]const u8 = @ptrCast(a);
try expect(&a[1] - &b[0] == 1);
}
comptime {
var x: [64][64]u8 = undefined;
const a = &x[0][12];
const b = &x[15][3];
try expect(b - a == 951);
}
}
test "double pointer parsing" {
comptime assert(PtrOf(PtrOf(i32)) == **i32);
}
@ -382,7 +438,7 @@ test "pointer to array at fixed address" {
try expect(@intFromPtr(&array[1]) == 0x14);
}
test "pointer arithmetic affects the alignment" {
test "pointer-integer arithmetic affects the alignment" {
{
var ptr: [*]align(8) u32 = undefined;
var x: usize = 1;

52
test/cases/compile_errors/invalid_pointer_arithmetic.zig Normal file
View file

@ -0,0 +1,52 @@
export fn a(x: [*]u8) void {
_ = x * 1;
}
export fn b(x: *u8) void {
_ = x * x;
}
export fn c() void {
const x: []u8 = undefined;
const y: []u8 = undefined;
_ = x - y;
}
export fn d() void {
var x: [*]u8 = undefined;
var y: [*]u16 = undefined;
_ = &x;
_ = &y;
_ = x - y;
}
comptime {
const x: *u8 = @ptrFromInt(1);
const y: *u16 = @ptrFromInt(2);
_ = x - y;
}
comptime {
const x: [*]u0 = @ptrFromInt(1);
_ = x + 1;
}
comptime {
const x: *u0 = @ptrFromInt(1);
const y: *u0 = @ptrFromInt(2);
_ = x - y;
}
// error
// backend=stage2
// target=native
//
// :2:11: error: invalid pointer-integer arithmetic operator
// :2:11: note: pointer-integer arithmetic only supports addition and subtraction
// :6:11: error: invalid pointer-pointer arithmetic operator
// :6:11: note: pointer-pointer arithmetic only supports subtraction
// :12:11: error: invalid operands to binary expression: 'Pointer' and 'Pointer'
// :20:11: error: incompatible pointer arithmetic operands '[*]u8' and '[*]u16'
// :26:11: error: incompatible pointer arithmetic operands '*u8' and '*u16'
// :31:11: error: pointer arithmetic requires element type 'u0' to have runtime bits
// :37:11: error: pointer arithmetic requires element type 'u0' to have runtime bits