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c backend: fix some inline assembly constraints #23794

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165 changes: 142 additions & 23 deletions src/codegen/c.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -5297,8 +5297,11 @@ fn airSwitchBr(f: *Function, inst: Air.Inst.Index, is_dispatch_loop: bool) !void
fn asmInputNeedsLocal(f: *Function, constraint: []const u8, value: CValue) bool {
const dg = f.object.dg;
const target = &dg.mod.resolved_target.result;
const brace_start = mem.indexOfScalar(u8, constraint, '{');
if (brace_start != null)
return true;

return switch (constraint[0]) {
'{' => true,
'i', 'r' => false,
'I' => !target.cpu.arch.isArm(),
else => switch (value) {
Expand Down Expand Up @@ -5347,21 +5350,58 @@ fn airAsm(f: *Function, inst: Air.Inst.Index) !CValue {

const locals_begin = @as(LocalIndex, @intCast(f.locals.items.len));
const constraints_extra_begin = extra_i;

// gcc and clang support at most 30 input + output + clobbers
var clobbers: [30]?[]const u8 = @splat(null);
var clobbered_inputs: [30]?usize = @splat(null);

for (outputs) |_| {
const extra_bytes = mem.sliceAsBytes(f.air.extra[extra_i..]);
const constraint = mem.sliceTo(extra_bytes, 0);
const name = mem.sliceTo(extra_bytes[constraint.len + 1 ..], 0);
// This equation accounts for the fact that even if we have exactly 4 bytes
// for the string, we still use the next u32 for the null terminator.
extra_i += (constraint.len + name.len + (2 + 3)) / 4;
}

for (inputs, 0..) |_, input_i| {
const extra_bytes = mem.sliceAsBytes(f.air.extra[extra_i..]);
const constraint = mem.sliceTo(extra_bytes, 0);
const name = mem.sliceTo(extra_bytes[constraint.len + 1 ..], 0);

clobbered_inputs[input_i] = extra_i;
// This equation accounts for the fact that even if we have exactly 4 bytes
// for the string, we still use the next u32 for the null terminator.
extra_i += (constraint.len + name.len + (2 + 3)) / 4;
}
for (0..clobbers_len) |clobber_i| {
const clobber = mem.sliceTo(mem.sliceAsBytes(f.air.extra[extra_i..]), 0);
// This equation accounts for the fact that even if we have exactly 4 bytes
// for the string, we still use the next u32 for the null terminator.
extra_i += clobber.len / 4 + 1;

clobbers[clobber_i] = clobber;
}

const end_of_clobbers = extra_i;
extra_i = constraints_extra_begin;

for (outputs) |output| {
const extra_bytes = mem.sliceAsBytes(f.air.extra[extra_i..]);
const constraint = mem.sliceTo(extra_bytes, 0);
const name = mem.sliceTo(extra_bytes[constraint.len + 1 ..], 0);
const brace_start = mem.indexOfScalar(u8, constraint, '{');
// This equation accounts for the fact that even if we have exactly 4 bytes
// for the string, we still use the next u32 for the null terminator.
extra_i += (constraint.len + name.len + (2 + 3)) / 4;

if (constraint.len < 2 or constraint[0] != '=' or
(constraint[1] == '{' and constraint[constraint.len - 1] != '}'))
if (constraint.len < 2 or (constraint[0] != '=' and constraint[0] != '+') or
(brace_start != null and constraint[constraint.len - 1] != '}'))
{
return f.fail("CBE: constraint not supported: '{s}'", .{constraint});
}

const is_reg = constraint[1] == '{';
const is_reg = brace_start != null;
if (is_reg) {
const output_ty = if (output == .none) inst_ty else f.typeOf(output).childType(zcu);
try writer.writeAll("register ");
Expand All @@ -5372,7 +5412,7 @@ fn airAsm(f: *Function, inst: Air.Inst.Index) !CValue {
try f.allocs.put(gpa, output_local.new_local, false);
try f.object.dg.renderTypeAndName(writer, output_ty, output_local, .{}, .none, .complete);
try writer.writeAll(" __asm(\"");
try writer.writeAll(constraint["={".len .. constraint.len - "}".len]);
try writer.writeAll(constraint[brace_start.? + "{".len .. constraint.len - "}".len]);
try writer.writeAll("\")");
if (f.wantSafety()) {
try writer.writeAll(" = ");
Expand All @@ -5381,21 +5421,76 @@ fn airAsm(f: *Function, inst: Air.Inst.Index) !CValue {
try writer.writeAll(";\n");
}
}
for (inputs) |input| {

for (0..inputs.len) |i| {
const input_i = inputs.len - i - 1;
const input = inputs[i];
const extra_bytes = mem.sliceAsBytes(f.air.extra[clobbered_inputs[input_i].?..]);
const constraint = mem.sliceTo(extra_bytes, 0);
const brace_start = mem.indexOfScalar(u8, constraint, '{');
if (brace_start == null) {
clobbered_inputs[input_i] = null;
continue;
}

const register_name = constraint[brace_start.? + "{".len .. constraint.len - "}".len];

if (register_name.len == 0) {
clobbered_inputs[input_i] = null;
continue;
}

var is_clobbered = false;
for (clobbers[0..clobbers_len]) |*clobber| {
if (clobber.* != null and std.mem.eql(u8, clobber.*.?, register_name)) {
is_clobbered = true;
clobber.* = null;
}
}

if (!is_clobbered) {
clobbered_inputs[input_i] = null;
continue;
}
if (brace_start.? != 0 or constraint[constraint.len - 1] != '}')
return f.fail("CBE: input linked to clobber with other constraints is not supported: '{s}'", .{constraint});

const input_ty = f.typeOf(input);
const input_val = try f.resolveInst(input);
try writer.writeAll("register ");
const input_local = try f.allocLocalValue(.{
.ctype = try f.ctypeFromType(input_ty, .complete),
.alignas = CType.AlignAs.fromAbiAlignment(input_ty.abiAlignment(zcu)),
});
try f.allocs.put(gpa, input_local.new_local, false);
try f.object.dg.renderTypeAndName(writer, input_ty, input_local, .{}, .none, .complete);
try writer.writeAll(" __asm(\"");
try writer.writeAll(constraint[brace_start.? + "{".len .. constraint.len - "}".len]);
try writer.writeAll("\")");
try writer.writeAll(" = ");
try f.writeCValue(writer, input_val, .Other);
try writer.writeAll(";\n");
}

for (inputs, 0..) |input, input_i| {
const extra_bytes = mem.sliceAsBytes(f.air.extra[extra_i..]);
const constraint = mem.sliceTo(extra_bytes, 0);
const name = mem.sliceTo(extra_bytes[constraint.len + 1 ..], 0);
const brace_start = mem.indexOfScalar(u8, constraint, '{');
// This equation accounts for the fact that even if we have exactly 4 bytes
// for the string, we still use the next u32 for the null terminator.
extra_i += (constraint.len + name.len + (2 + 3)) / 4;

// input is linked to a clobber, skip
if (clobbered_inputs[input_i] != null) continue;

if (constraint.len < 1 or mem.indexOfScalar(u8, "=+&%", constraint[0]) != null or
(constraint[0] == '{' and constraint[constraint.len - 1] != '}'))
(brace_start != null and constraint[constraint.len - 1] != '}'))
{
return f.fail("CBE: constraint not supported: '{s}'", .{constraint});
}

const is_reg = constraint[0] == '{';
const is_reg = brace_start != null;
const input_val = try f.resolveInst(input);
if (asmInputNeedsLocal(f, constraint, input_val)) {
const input_ty = f.typeOf(input);
Expand All @@ -5405,23 +5500,20 @@ fn airAsm(f: *Function, inst: Air.Inst.Index) !CValue {
.alignas = CType.AlignAs.fromAbiAlignment(input_ty.abiAlignment(zcu)),
});
try f.allocs.put(gpa, input_local.new_local, false);
try f.object.dg.renderTypeAndName(writer, input_ty, input_local, Const, .none, .complete);
// gcc's docs indicates to not use the const qualifier as the compiler may optimize away the declaration
try f.object.dg.renderTypeAndName(writer, input_ty, input_local, .{}, .none, .complete);
if (is_reg) {
try writer.writeAll(" __asm(\"");
try writer.writeAll(constraint["{".len .. constraint.len - "}".len]);
try writer.writeAll(constraint[brace_start.? + "{".len .. constraint.len - "}".len]);
try writer.writeAll("\")");
}
try writer.writeAll(" = ");
try f.writeCValue(writer, input_val, .Other);
try writer.writeAll(";\n");
}
}
for (0..clobbers_len) |_| {
const clobber = mem.sliceTo(mem.sliceAsBytes(f.air.extra[extra_i..]), 0);
// This equation accounts for the fact that even if we have exactly 4 bytes
// for the string, we still use the next u32 for the null terminator.
extra_i += clobber.len / 4 + 1;
}

extra_i = end_of_clobbers;

{
const asm_source = mem.sliceAsBytes(f.air.extra[extra_i..])[0..extra.data.source_len];
Expand Down Expand Up @@ -5450,7 +5542,7 @@ fn airAsm(f: *Function, inst: Air.Inst.Index) !CValue {
dst_i += 1;

if (asm_source[src_i] != '[') {
// This also handles %%
// This also handles %% and %=
fixed_asm_source[dst_i] = asm_source[src_i];
src_i += 1;
dst_i += 1;
Expand Down Expand Up @@ -5481,19 +5573,40 @@ fn airAsm(f: *Function, inst: Air.Inst.Index) !CValue {
extra_i = constraints_extra_begin;
var locals_index = locals_begin;
try writer.writeByte(':');
for (outputs, 0..) |output, index| {
var output_index: usize = 0;
for (clobbered_inputs[0..inputs.len]) |in_extra_i| {
if (in_extra_i == null) continue;

const extra_bytes = mem.sliceAsBytes(f.air.extra[in_extra_i.?..]);
const constraint = mem.sliceTo(extra_bytes, 0);
const name = mem.sliceTo(extra_bytes[constraint.len + 1 ..], 0);

if (output_index > 0) try writer.writeByte(',');
try writer.writeByte(' ');
if (!mem.eql(u8, name, "_")) try writer.print("[{s}]", .{name});
try writer.writeAll("\"+r\"(");

try f.writeCValue(writer, .{ .local = locals_index }, .Other);
locals_index += 1;
try writer.writeByte(')');

output_index += 1;
}

for (outputs) |output| {
const extra_bytes = mem.sliceAsBytes(f.air.extra[extra_i..]);
const constraint = mem.sliceTo(extra_bytes, 0);
const name = mem.sliceTo(extra_bytes[constraint.len + 1 ..], 0);
const brace_start = mem.indexOfScalar(u8, constraint, '{');
// This equation accounts for the fact that even if we have exactly 4 bytes
// for the string, we still use the next u32 for the null terminator.
extra_i += (constraint.len + name.len + (2 + 3)) / 4;

if (index > 0) try writer.writeByte(',');
if (output_index > 0) try writer.writeByte(',');
try writer.writeByte(' ');
if (!mem.eql(u8, name, "_")) try writer.print("[{s}]", .{name});
const is_reg = constraint[1] == '{';
try writer.print("{s}(", .{fmtStringLiteral(if (is_reg) "=r" else constraint, null)});
const is_reg = brace_start != null;
try writer.print("{s}(", .{fmtStringLiteral(if (is_reg) constraint[0..brace_start.?] else constraint, if (is_reg) 'r' else null)});
if (is_reg) {
try f.writeCValue(writer, .{ .local = locals_index }, .Other);
locals_index += 1;
Expand All @@ -5503,6 +5616,7 @@ fn airAsm(f: *Function, inst: Air.Inst.Index) !CValue {
try f.writeCValueDeref(writer, try f.resolveInst(output));
}
try writer.writeByte(')');
output_index += 1;
}
try writer.writeByte(':');
for (inputs, 0..) |input, index| {
Expand All @@ -5513,11 +5627,14 @@ fn airAsm(f: *Function, inst: Air.Inst.Index) !CValue {
// for the string, we still use the next u32 for the null terminator.
extra_i += (constraint.len + name.len + (2 + 3)) / 4;

// if input is linked to a clobber, skip
if (clobbered_inputs[index] != null) continue;

if (index > 0) try writer.writeByte(',');
try writer.writeByte(' ');
if (!mem.eql(u8, name, "_")) try writer.print("[{s}]", .{name});

const is_reg = constraint[0] == '{';
const is_reg = mem.indexOfScalar(u8, constraint, '{') != null;
const input_val = try f.resolveInst(input);
try writer.print("{s}(", .{fmtStringLiteral(if (is_reg) "r" else constraint, null)});
try f.writeCValue(writer, if (asmInputNeedsLocal(f, constraint, input_val)) local: {
Expand All @@ -5534,6 +5651,8 @@ fn airAsm(f: *Function, inst: Air.Inst.Index) !CValue {
// for the string, we still use the next u32 for the null terminator.
extra_i += clobber.len / 4 + 1;

// if a clobber is linked to an input, clobbers[clobber_i] is null
if (clobbers[clobber_i] == null) continue;
if (clobber.len == 0) continue;

if (clobber_i > 0) try writer.writeByte(',');
Expand All @@ -5551,7 +5670,7 @@ fn airAsm(f: *Function, inst: Air.Inst.Index) !CValue {
// for the string, we still use the next u32 for the null terminator.
extra_i += (constraint.len + name.len + (2 + 3)) / 4;

const is_reg = constraint[1] == '{';
const is_reg = mem.indexOfScalar(u8, constraint, '{') != null;
if (is_reg) {
try f.writeCValueDeref(writer, if (output == .none)
.{ .local_ref = inst_local.new_local }
Expand Down
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