Skip to content

translate-c: Don't discard variables unless necessary #9306

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
andrewrk merged 1 commit into from
Jul 5, 2021
Merged

translate-c: Don't discard variables unless necessary #9306

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
68 changes: 53 additions & 15 deletions src/translate_c.zig
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -67,6 +67,12 @@ const Scope = struct {
mangle_count: u32 = 0,
label: ?[]const u8 = null,

/// By default all variables are discarded, since we do not know in advance if they
/// will be used. This maps the variable's name to the Discard payload, so that if
/// the variable is subsequently referenced we can indicate that the discard should
/// be skipped during the intermediate AST -> Zig AST render step.
variable_discards: std.StringArrayHashMap(*ast.Payload.Discard),

/// When the block corresponds to a function, keep track of the return type
/// so that the return expression can be cast, if necessary
return_type: ?clang.QualType = null,
Expand All @@ -84,6 +90,7 @@ const Scope = struct {
},
.statements = std.ArrayList(Node).init(c.gpa),
.variables = AliasList.init(c.gpa),
.variable_discards = std.StringArrayHashMap(*ast.Payload.Discard).init(c.gpa),
};
if (labeled) {
blk.label = try blk.makeMangledName(c, "blk");
Expand All @@ -94,6 +101,7 @@ const Scope = struct {
fn deinit(self: *Block) void {
self.statements.deinit();
self.variables.deinit();
self.variable_discards.deinit();
self.* = undefined;
}

Expand Down Expand Up @@ -154,8 +162,9 @@ const Scope = struct {

fn discardVariable(scope: *Block, c: *Context, name: []const u8) Error!void {
const name_node = try Tag.identifier.create(c.arena, name);
const discard = try Tag.discard.create(c.arena, name_node);
const discard = try Tag.discard.create(c.arena, .{ .should_skip = false, .value = name_node });
try scope.statements.append(discard);
try scope.variable_discards.putNoClobber(name, discard.castTag(.discard).?);
}
};

Expand Down Expand Up @@ -271,6 +280,24 @@ const Scope = struct {
}
}
}

fn skipVariableDiscard(inner: *Scope, name: []const u8) void {
var scope = inner;
while (true) {
switch (scope.id) {
.root => return,
.block => {
const block = @fieldParentPtr(Block, "base", scope);
if (block.variable_discards.get(name)) |discard| {
discard.data.should_skip = true;
return;
}
},
else => {},
}
scope = scope.parent.?;
}
}
};

pub const Context = struct {
Expand Down Expand Up @@ -834,7 +861,9 @@ fn transTypeDef(c: *Context, scope: *Scope, typedef_decl: *const clang.TypedefNa
try addTopLevelDecl(c, name, node);
} else {
try scope.appendNode(node);
try bs.discardVariable(c, name);
if (node.tag() != .pub_var_simple) {
try bs.discardVariable(c, name);
}
}
}

Expand Down Expand Up @@ -1078,14 +1107,16 @@ fn transRecordDecl(c: *Context, scope: *Scope, record_decl: *const clang.RecordD
.init = init_node,
},
};

const node = Node.initPayload(&payload.base);
if (toplevel) {
try addTopLevelDecl(c, name, Node.initPayload(&payload.base));
try addTopLevelDecl(c, name, node);
if (!is_unnamed)
try c.alias_list.append(.{ .alias = bare_name, .name = name });
} else {
try scope.appendNode(Node.initPayload(&payload.base));
try bs.discardVariable(c, name);
try scope.appendNode(node);
if (node.tag() != .pub_var_simple) {
try bs.discardVariable(c, name);
}
}
}

Expand Down Expand Up @@ -1172,14 +1203,16 @@ fn transEnumDecl(c: *Context, scope: *Scope, enum_decl: *const clang.EnumDecl) E
.name = name,
},
};

const node = Node.initPayload(&payload.base);
if (toplevel) {
try addTopLevelDecl(c, name, Node.initPayload(&payload.base));
try addTopLevelDecl(c, name, node);
if (!is_unnamed)
try c.alias_list.append(.{ .alias = bare_name, .name = name });
} else {
try scope.appendNode(Node.initPayload(&payload.base));
try bs.discardVariable(c, name);
try scope.appendNode(node);
if (node.tag() != .pub_var_simple) {
try bs.discardVariable(c, name);
}
}
}

Expand Down Expand Up @@ -1789,7 +1822,7 @@ fn transDeclStmtOne(
args[0] = try Tag.address_of.create(c.arena, varname);

const cleanup_call = try Tag.call.create(c.arena, .{ .lhs = fn_id, .args = args });
const discard = try Tag.discard.create(c.arena, cleanup_call);
const discard = try Tag.discard.create(c.arena, .{ .should_skip = false, .value = cleanup_call });
const deferred_cleanup = try Tag.@"defer".create(c.arena, discard);

try block_scope.statements.append(deferred_cleanup);
Expand Down Expand Up @@ -1844,6 +1877,7 @@ fn transDeclRefExpr(
});
}
}
scope.skipVariableDiscard(mangled_name);
return ref_expr;
}

Expand Down Expand Up @@ -2478,7 +2512,9 @@ fn transInitListExprRecord(
.value = try transExpr(c, scope, elem_expr, .used),
});
}

if (ty_node.castTag(.identifier)) |ident_node| {
scope.skipVariableDiscard(ident_node.data);
}
return Tag.container_init.create(c.arena, .{
.lhs = ty_node,
.inits = try c.arena.dupe(ast.Payload.ContainerInit.Initializer, field_inits.items),
Expand Down Expand Up @@ -3870,7 +3906,7 @@ fn maybeSuppressResult(
) TransError!Node {
_ = scope;
if (used == .used) return result;
return Tag.discard.create(c.arena, result);
return Tag.discard.create(c.arena, .{ .should_skip = false, .value = result });
}

fn addTopLevelDecl(c: *Context, name: []const u8, decl_node: Node) !void {
Expand Down Expand Up @@ -5004,7 +5040,7 @@ fn parseCExpr(c: *Context, m: *MacroCtx, scope: *Scope) ParseError!Node {
var last = node;
while (true) {
// suppress result
const ignore = try Tag.discard.create(c.arena, last);
const ignore = try Tag.discard.create(c.arena, .{ .should_skip = false, .value = last });
try block_scope.statements.append(ignore);

last = try parseCCondExpr(c, m, scope);
Expand Down Expand Up @@ -5303,7 +5339,9 @@ fn parseCPrimaryExprInner(c: *Context, m: *MacroCtx, scope: *Scope) ParseError!N
try m.fail(c, "TODO implement function '{s}' in std.c.builtins", .{mangled_name});
return error.ParseError;
}
return Tag.identifier.create(c.arena, builtin_typedef_map.get(mangled_name) orelse mangled_name);
const identifier = try Tag.identifier.create(c.arena, builtin_typedef_map.get(mangled_name) orelse mangled_name);
scope.skipVariableDiscard(identifier.castTag(.identifier).?.data);
return identifier;
},
.LParen => {
const inner_node = try parseCExpr(c, m, scope);
Expand Down
14 changes: 12 additions & 2 deletions src/translate_c/ast.zig
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -248,7 +248,6 @@ pub const Node = extern union {
.@"comptime",
.@"defer",
.asm_simple,
.discard,
.std_math_Log2Int,
.negate,
.negate_wrap,
Expand Down Expand Up @@ -341,6 +340,7 @@ pub const Node = extern union {
.warning,
.type,
=> Payload.Value,
.discard => Payload.Discard,
.@"if" => Payload.If,
.@"while" => Payload.While,
.@"switch", .array_init, .switch_prong => Payload.Switch,
Expand Down Expand Up @@ -463,6 +463,14 @@ pub const Payload = struct {
},
};

pub const Discard = struct {
base: Payload,
data: struct {
should_skip: bool,
value: Node,
},
};

pub const If = struct {
base: Payload,
data: struct {
Expand Down Expand Up @@ -1491,6 +1499,8 @@ fn renderNode(c: *Context, node: Node) Allocator.Error!NodeIndex {
.pub_inline_fn => return renderMacroFunc(c, node),
.discard => {
const payload = node.castTag(.discard).?.data;
if (payload.should_skip) return @as(NodeIndex, 0);

const lhs = try c.addNode(.{
.tag = .identifier,
.main_token = try c.addToken(.identifier, "_"),
Expand All @@ -1501,7 +1511,7 @@ fn renderNode(c: *Context, node: Node) Allocator.Error!NodeIndex {
.main_token = try c.addToken(.equal, "="),
.data = .{
.lhs = lhs,
.rhs = try renderNode(c, payload),
.rhs = try renderNode(c, payload.value),
},
});
},
Expand Down
Loading