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C backend: basic big ints, fix airPtrToInt, array references, pointer arithmetic UB with NULL, implement airPtrElemPtr/Val, fix redundant indirection/references with arrays

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-add additional test cases that were found to be passing
-add basic int128 test cases which previously did not pass but weren't covered
-most test cases in cast.zig now pass
-i128/u128 or smaller int constants can now be rendered
-unsigned int constants are now always suffixed with 'u' to prevent random compile errors
-pointers with a val tag of 'zero' now just emit a 0 constant which coerces to the pointer type and fixes some warnings with ordered comparisons
-pointers with a val tag of 'one' are now casted back to the pointer type
-support pointers with a u64 val
-fix bug where rendering an array's type will emit more indirection than is needed
-render uint128_t/int128_t manually when needed
-implement ptr_add/sub AIR handlers manually so they manually cast to int types which avoids UB if the result or ptr operand is NULL
-implement airPtrElemVal/Ptr
-airAlloc for arrays will not allocate a ref as the local for the array is already a reference/pointer to the array itself
-fix airPtrToInt by casting to the int type
This commit is contained in:
drew
2021-11-14 18:28:44 -08:00
committed by Andrew Kelley
parent 952d865bd2
commit 9bf1681990
6 changed files with 443 additions and 270 deletions
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166
src/codegen/c.zig
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@@ -226,6 +226,36 @@ pub const DeclGen = struct {
try dg.renderDeclName(decl, writer);
}
/// Assumes that int_val is an int greater than maxInt(u64) and has > 64 and <= 128 bits.
fn renderBigInt(
writer: anytype,
int_val: anytype,
) error{ OutOfMemory, AnalysisFail }!void {
const int_info = @typeInfo(@TypeOf(int_val)).Int;
const is_signed = int_info.signedness == .signed;
const is_neg = int_val < 0;
comptime assert(int_info.bits > 64 and int_info.bits <= 128);
// Clang and GCC don't support 128-bit integer constants but will hopefully unfold them
// if we construct one manually.
const magnitude = std.math.absCast(int_val);
const high = @truncate(u64, magnitude >> 64);
const low = @truncate(u64, magnitude);
// (int128_t)/<->( ( (uint128_t)( val_high << 64 )u ) + (uint128_t)val_low/u )
if (is_signed) try writer.writeAll("(int128_t)");
if (is_neg) try writer.writeByte('-');
assert(high > 0);
try writer.print("(((uint128_t)0x{x}u<<64)", .{ high });
if (low > 0)
try writer.print("+(uint128_t)0x{x}u", .{ low });
return writer.writeByte(')');
}
fn renderValue(
dg: *DeclGen,
writer: anytype,
@@ -240,18 +270,18 @@ pub const DeclGen = struct {
const c_bits = toCIntBits(ty.intInfo(dg.module.getTarget()).bits) orelse
return dg.fail("TODO: C backend: implement integer types larger than 128 bits", .{});
switch (c_bits) {
8 => return writer.writeAll("0xaaU"),
16 => return writer.writeAll("0xaaaaU"),
32 => return writer.writeAll("0xaaaaaaaaU"),
64 => return writer.writeAll("0xaaaaaaaaaaaaaaaaUL"),
128 => return writer.writeAll("0xaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaULL"),
8 => return writer.writeAll("0xaau"),
16 => return writer.writeAll("0xaaaau"),
32 => return writer.writeAll("0xaaaaaaaau"),
64 => return writer.writeAll("0xaaaaaaaaaaaaaaaau"),
128 => return renderBigInt(writer, @as(u128, 0xaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa)),
else => unreachable,
}
},
.Float => {
switch (ty.floatBits(dg.module.getTarget())) {
32 => return writer.writeAll("zig_bitcast_f32_u32(0xaaaaaaaa)"),
64 => return writer.writeAll("zig_bitcast_f64_u64(0xaaaaaaaaaaaaaaaa)"),
32 => return writer.writeAll("zig_bitcast_f32_u32(0xaaaaaaaau)"),
64 => return writer.writeAll("zig_bitcast_f64_u64(0xaaaaaaaaaaaaaaaau)"),
else => return dg.fail("TODO float types > 64 bits are not support in renderValue() as of now", .{}),
}
},
@@ -265,10 +295,18 @@ pub const DeclGen = struct {
}
}
switch (ty.zigTypeTag()) {
.Int => {
if (ty.isSignedInt())
return writer.print("{d}", .{val.toSignedInt()});
return writer.print("{d}", .{val.toUnsignedInt()});
.Int => switch (val.tag()) {
.int_big_positive => try renderBigInt(writer, val.castTag(.int_big_positive).?.asBigInt().to(u128) catch {
return dg.fail("TODO implement integer constants larger than 128 bits", .{});
}),
.int_big_negative => try renderBigInt(writer, val.castTag(.int_big_negative).?.asBigInt().to(i128) catch {
return dg.fail("TODO implement integer constants larger than 128 bits", .{});
}),
else => {
if (ty.isSignedInt())
return writer.print("{d}", .{val.toSignedInt()});
return writer.print("{d}u", .{val.toUnsignedInt()});
}
},
.Float => {
if (ty.floatBits(dg.module.getTarget()) <= 64) {
@@ -286,8 +324,17 @@ pub const DeclGen = struct {
return dg.fail("TODO: C backend: implement lowering large float values", .{});
},
.Pointer => switch (val.tag()) {
.null_value, .zero => try writer.writeAll("NULL"),
.one => try writer.writeAll("1"),
.null_value => try writer.writeAll("NULL"),
// Technically this should produce NULL but the integer literal 0 will always coerce
// to the assigned pointer type. Note this is just a hack to fix warnings from ordered comparisons (<, >, etc)
// between pointers and 0, which is an extension to begin with.
.zero => try writer.writeByte('0'),
.one => {
// int constants like 1 will not cast to the pointer however.
try writer.writeAll("((");
try dg.renderType(writer, ty);
return writer.writeAll(")1)");
},
.decl_ref => {
const decl = val.castTag(.decl_ref).?.data;
return dg.renderDeclValue(writer, ty, val, decl);
@@ -316,6 +363,11 @@ pub const DeclGen = struct {
const decl = val.castTag(.extern_fn).?.data;
try dg.renderDeclName(decl, writer);
},
.int_u64 => {
try writer.writeAll("((");
try dg.renderType(writer, ty);
try writer.print(")0x{x}u)", .{val.toUnsignedInt()});
},
else => unreachable,
},
.Array => {
@@ -728,6 +780,8 @@ pub const DeclGen = struct {
.i32 => try w.writeAll("int32_t"),
.u64 => try w.writeAll("uint64_t"),
.i64 => try w.writeAll("int64_t"),
.u128 => try w.writeAll("uint128_t"),
.i128 => try w.writeAll("int128_t"),
.usize => try w.writeAll("uintptr_t"),
.isize => try w.writeAll("intptr_t"),
.c_short => try w.writeAll("short"),
@@ -787,8 +841,9 @@ pub const DeclGen = struct {
},
.Array => {
// We are referencing the array so it will decay to a C pointer.
try dg.renderType(w, t.elemType());
return w.writeAll(" *");
// NB: arrays are not really types in C so they are either specified in the declaration
// or are already pointed to; our only job is to render the element's type.
return dg.renderType(w, t.elemType());
},
.Optional => {
var opt_buf: Type.Payload.ElemType = undefined;
@@ -1068,12 +1123,15 @@ fn genBody(f: *Function, body: []const Air.Inst.Index) error{ AnalysisFail, OutO
.unreach => try airUnreach(f),
.fence => try airFence(f, inst),
.ptr_add => try airPtrAddSub (f, inst, " + "),
.ptr_sub => try airPtrAddSub (f, inst, " - "),
// TODO use a different strategy for add that communicates to the optimizer
// that wrapping is UB.
.add, .ptr_add => try airBinOp (f, inst, " + "),
.add => try airBinOp (f, inst, " + "),
// TODO use a different strategy for sub that communicates to the optimizer
// that wrapping is UB.
.sub, .ptr_sub => try airBinOp (f, inst, " - "),
.sub => try airBinOp (f, inst, " - "),
// TODO use a different strategy for mul that communicates to the optimizer
// that wrapping is UB.
.mul => try airBinOp (f, inst, " * "),
@@ -1187,7 +1245,7 @@ fn genBody(f: *Function, body: []const Air.Inst.Index) error{ AnalysisFail, OutO
.ptr_slice_len_ptr => try airPtrSliceFieldPtr(f, inst, ".len;\n"),
.ptr_slice_ptr_ptr => try airPtrSliceFieldPtr(f, inst, ".ptr;\n"),
.ptr_elem_val => try airPtrElemVal(f, inst, "["),
.ptr_elem_val => try airPtrElemVal(f, inst),
.ptr_elem_ptr => try airPtrElemPtr(f, inst),
.slice_elem_val => try airSliceElemVal(f, inst),
.slice_elem_ptr => try airSliceElemPtr(f, inst),
@@ -1240,20 +1298,39 @@ fn airPtrSliceFieldPtr(f: *Function, inst: Air.Inst.Index, suffix: []const u8) !
return f.fail("TODO: C backend: airPtrSliceFieldPtr", .{});
}
fn airPtrElemVal(f: *Function, inst: Air.Inst.Index, prefix: []const u8) !CValue {
const is_volatile = false; // TODO
if (!is_volatile and f.liveness.isUnused(inst))
return CValue.none;
fn airPtrElemVal(f: *Function, inst: Air.Inst.Index) !CValue {
const bin_op = f.air.instructions.items(.data)[inst].bin_op;
const slice_ty = f.air.typeOf(bin_op.lhs);
if (!slice_ty.isVolatilePtr() and f.liveness.isUnused(inst)) return CValue.none;
_ = prefix;
return f.fail("TODO: C backend: airPtrElemVal", .{});
const arr = try f.resolveInst(bin_op.lhs);
const index = try f.resolveInst(bin_op.rhs);
const writer = f.object.writer();
const local = try f.allocLocal(f.air.typeOfIndex(inst), .Const);
try writer.writeAll(" = ");
try f.writeCValue(writer, arr);
try writer.writeByte('[');
try f.writeCValue(writer, index);
try writer.writeAll("];\n");
return local;
}
fn airPtrElemPtr(f: *Function, inst: Air.Inst.Index) !CValue {
if (f.liveness.isUnused(inst))
return CValue.none;
if (f.liveness.isUnused(inst)) return CValue.none;
return f.fail("TODO: C backend: airPtrElemPtr", .{});
const ty_pl = f.air.instructions.items(.data)[inst].ty_pl;
const bin_op = f.air.extraData(Air.Bin, ty_pl.payload).data;
const arr = try f.resolveInst(bin_op.lhs);
const index = try f.resolveInst(bin_op.rhs);
const writer = f.object.writer();
const local = try f.allocLocal(f.air.typeOfIndex(inst), .Const);
try writer.writeAll(" = &");
try f.writeCValue(writer, arr);
try writer.writeByte('[');
try f.writeCValue(writer, index);
try writer.writeAll("];\n");
return local;
}
fn airSliceElemVal(f: *Function, inst: Air.Inst.Index) !CValue {
@@ -1317,6 +1394,10 @@ fn airAlloc(f: *Function, inst: Air.Inst.Index) !CValue {
const local = try f.allocLocal(elem_type, mutability);
try writer.writeAll(";\n");
// Arrays are already pointers so they don't need to be referenced.
if (elem_type.zigTypeTag() == .Array)
return CValue{ .local = local.local };
return CValue{ .local_ref = local.local };
}
@@ -1810,6 +1891,33 @@ fn airBinOp(f: *Function, inst: Air.Inst.Index, operator: [*:0]const u8) !CValue
return local;
}
fn airPtrAddSub(f: *Function, inst: Air.Inst.Index, operator: [*:0]const u8) !CValue {
if (f.liveness.isUnused(inst))
return CValue.none;
const bin_op = f.air.instructions.items(.data)[inst].bin_op;
const lhs = try f.resolveInst(bin_op.lhs);
const rhs = try f.resolveInst(bin_op.rhs);
const writer = f.object.writer();
const inst_ty = f.air.typeOfIndex(inst);
const local = try f.allocLocal(inst_ty, .Const);
// We must convert to and from integer types to prevent UB if the operation results in a NULL pointer,
// or if LHS is NULL. The operation is only UB if the result is NULL and then dereferenced.
try writer.writeAll(" = (");
try f.renderType(writer, inst_ty);
try writer.writeAll(")(((uintptr_t)");
try f.writeCValue(writer, lhs);
try writer.print("){s}(", .{operator});
try f.writeCValue(writer, rhs);
try writer.writeAll("*sizeof(");
try f.renderType(writer, inst_ty.childType());
try writer.print(")));\n", .{});
return local;
}
fn airMinMax(f: *Function, inst: Air.Inst.Index, operator: [*:0]const u8) !CValue {
if (f.liveness.isUnused(inst)) return CValue.none;
@@ -2529,7 +2637,9 @@ fn airPtrToInt(f: *Function, inst: Air.Inst.Index) !CValue {
const writer = f.object.writer();
const operand = try f.resolveInst(un_op);
try writer.writeAll(" = ");
try writer.writeAll(" = (");
try f.renderType(writer, inst_ty);
try writer.writeAll(")");
try f.writeCValue(writer, operand);
try writer.writeAll(";\n");
return local;