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runtime: eliminate scase.kind field

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This is the gofrontend version of https://golang.org/cl/245125.

Original CL description:

    Currently, we include a "kind" field on scase to distinguish the three
    kinds of cases in a select statement: sends, receives, and defaults.

    This commit removes by kind field by instead arranging for the
    compiler to always place sends before receives, and to provide their
    counts separately. It also passes an explicit "block bool" parameter
    to avoid needing to include a default case in the array.

    It's safe to shuffle cases like this because the runtime will
    randomize the order they're polled in anyway.

    For golang/go#40410.

This is being brought over to gofrontend as a step toward upgrading to
Go1.16beta1.

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/279735
This commit is contained in:
Ian Lance Taylor 2020-12-22 11:04:35 -08:00
parent 6aff491f7b
commit 313890530c
6 changed files with 182 additions and 103 deletions
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2
gcc/go/gofrontend/MERGE
View File

@ -1,4 +1,4 @@
eca96e39cb895805b617e0e1f184f893ed3e46bb
d091cd25a5894ac751fe1868197648fc486cf322
The first line of this file holds the git revision number of the last
merge done from the gofrontend repository.

4
gcc/go/gofrontend/runtime.def
View File

@ -195,8 +195,8 @@ DEF_GO_RUNTIME(CHANRECV2, "runtime.chanrecv2", P2(CHAN, POINTER), R1(BOOL))
// Run a select, returning the index of the selected clause and
// whether that channel received a value.
DEF_GO_RUNTIME(SELECTGO, "runtime.selectgo", P3(POINTER, POINTER, INT),
R2(INT, BOOL))
DEF_GO_RUNTIME(SELECTGO, "runtime.selectgo",
P5(POINTER, POINTER, INT, INT, BOOL), R2(INT, BOOL))
// Non-blocking send a value on a channel, used for two-case select
// statement with a default case.

131
gcc/go/gofrontend/statements.cc
View File

@ -5291,22 +5291,23 @@ Select_clauses::Select_clause::traverse(Traverse* traverse)
void
Select_clauses::Select_clause::lower(Gogo* gogo, Named_object* function,
Block* b, Temporary_statement* scases,
size_t index, Temporary_statement* recvok)
int index, Temporary_statement* recvok)
{
Location loc = this->location_;
Expression* scase = Expression::make_temporary_reference(scases, loc);
Expression* index_expr = Expression::make_integer_ul(index, NULL, loc);
scase = Expression::make_array_index(scase, index_expr, NULL, NULL, loc);
this->set_case_index(index);
if (this->is_default_)
{
go_assert(this->channel_ == NULL && this->val_ == NULL);
this->lower_default(b, scase);
this->is_lowered_ = true;
return;
}
Expression* scase = Expression::make_temporary_reference(scases, loc);
Expression* index_expr = Expression::make_integer_sl(index, NULL, loc);
scase = Expression::make_array_index(scase, index_expr, NULL, NULL, loc);
// Evaluate the channel before the select statement.
Temporary_statement* channel_temp = Statement::make_temporary(NULL,
this->channel_,
@ -5326,15 +5327,6 @@ Select_clauses::Select_clause::lower(Gogo* gogo, Named_object* function,
this->val_ = NULL;
}
// Lower a default clause in a select statement.
void
Select_clauses::Select_clause::lower_default(Block* b, Expression* scase)
{
Location loc = this->location_;
this->set_case(b, scase, Expression::make_nil(loc), NULL, caseDefault);
}
// Lower a send clause in a select statement.
void
@ -5366,7 +5358,7 @@ Select_clauses::Select_clause::lower_send(Block* b, Expression* scase,
Type* unsafe_pointer_type = Type::make_pointer_type(Type::make_void_type());
valaddr = Expression::make_cast(unsafe_pointer_type, valaddr, loc);
this->set_case(b, scase, chanref, valaddr, caseSend);
this->set_case(b, scase, chanref, valaddr);
}
// Lower a receive clause in a select statement.
@ -5392,7 +5384,7 @@ Select_clauses::Select_clause::lower_recv(Gogo* gogo, Named_object* function,
Type* unsafe_pointer_type = Type::make_pointer_type(Type::make_void_type());
valaddr = Expression::make_cast(unsafe_pointer_type, valaddr, loc);
this->set_case(b, scase, chanref, valaddr, caseRecv);
this->set_case(b, scase, chanref, valaddr);
// If the block of statements is executed, arrange for the received
// value to move from VAL to the place where the statements expect
@ -5447,8 +5439,7 @@ void
Select_clauses::Select_clause::set_case(Block* b,
Expression* scase,
Expression* chanref,
Expression* elem,
int kind)
Expression* elem)
{
Location loc = this->location_;
Struct_type* scase_type = scase->type()->struct_type();
@ -5469,14 +5460,6 @@ Select_clauses::Select_clause::set_case(Block* b,
s = Statement::make_assignment(ref, elem, loc);
b->add_statement(s);
}
field_index = 2;
go_assert(scase_type->field(field_index)->is_field_name("kind"));
Type* uint16_type = Type::lookup_integer_type("uint16");
Expression* k = Expression::make_integer_ul(kind, uint16_type, loc);
ref = Expression::make_field_reference(scase->copy(), field_index, loc);
s = Statement::make_assignment(ref, k, loc);
b->add_statement(s);
}
// Determine types.
@ -5577,6 +5560,19 @@ Select_clauses::Select_clause::dump_clause(
// Class Select_clauses.
// Whether there is a default case.
bool
Select_clauses::has_default() const
{
for (Clauses::const_iterator p = this->clauses_.begin();
p != this->clauses_.end();
++p)
if (p->is_default())
return true;
return false;
}
// Traversal.
int
@ -5594,17 +5590,60 @@ Select_clauses::traverse(Traverse* traverse)
// Lowering. Here we pull out the channel and the send values, to
// enforce the order of evaluation. We also add explicit send and
// receive statements to the clauses.
// receive statements to the clauses. This builds the entries in the
// local array of scase values. It sets *P_SEND_COUNT and
// *P_RECV_COUNT.
void
Select_clauses::lower(Gogo* gogo, Named_object* function, Block* b,
Temporary_statement* scases, Temporary_statement* recvok)
Temporary_statement* scases, Temporary_statement* recvok,
int *p_send_count, int *p_recv_count)
{
size_t i = 0;
int send_count = 0;
int recv_count = 0;
bool has_default = false;
for (Clauses::iterator p = this->clauses_.begin();
p != this->clauses_.end();
++p, ++i)
p->lower(gogo, function, b, scases, i, recvok);
++p)
{
if (p->is_default())
has_default = true;
else if (p->is_send())
++send_count;
else
++recv_count;
}
*p_send_count = send_count;
*p_recv_count = recv_count;
int send_index = 0;
int recv_index = send_count;
for (Clauses::iterator p = this->clauses_.begin();
p != this->clauses_.end();
++p)
{
int index;
if (p->is_default())
index = -1;
else if (p->is_send())
{
index = send_index;
++send_index;
}
else
{
index = recv_index;
++recv_index;
}
p->lower(gogo, function, b, scases, index, recvok);
}
go_assert(send_index == send_count);
go_assert(recv_index == send_count + recv_count);
go_assert(static_cast<size_t>(recv_index + (has_default ? 1 : 0))
== this->size());
}
// Determine types.
@ -5664,7 +5703,8 @@ Select_clauses::get_backend(Translate_context* context,
p != this->clauses_.end();
++p, ++i)
{
Expression* index_expr = Expression::make_integer_ul(i, int_type,
Expression* index_expr = Expression::make_integer_sl(p->case_index(),
int_type,
location);
cases[i].push_back(index_expr->get_backend(context));
@ -5749,6 +5789,7 @@ Select_statement::do_lower(Gogo* gogo, Named_object* function,
Block* b = new Block(enclosing, loc);
int ncases = this->clauses_->size();
bool has_default = this->clauses_->has_default();
// Zero-case select. Just block the execution.
if (ncases == 0)
@ -5766,11 +5807,13 @@ Select_statement::do_lower(Gogo* gogo, Named_object* function,
// Two-case select with one default case. It is a non-blocking
// send/receive.
if (ncases == 2
&& (this->clauses_->at(0).is_default()
|| this->clauses_->at(1).is_default()))
if (ncases == 2 && has_default)
return this->lower_two_case(b);
// We don't allocate an entry in scases for the default case.
if (has_default)
--ncases;
Type* scase_type = Channel_type::select_case_type();
Expression* ncases_expr =
Expression::make_integer_ul(ncases, NULL,
@ -5803,7 +5846,10 @@ Select_statement::do_lower(Gogo* gogo, Named_object* function,
b->add_statement(recvok);
// Initialize the scases array.
this->clauses_->lower(gogo, function, b, scases, recvok);
int send_count;
int recv_count;
this->clauses_->lower(gogo, function, b, scases, recvok, &send_count,
&recv_count);
// Build the call to selectgo. Later, in do_get_backend, we will
// build a switch on the result that branches to the various cases.
@ -5817,11 +5863,18 @@ Select_statement::do_lower(Gogo* gogo, Named_object* function,
order_ref = Expression::make_unary(OPERATOR_AND, order_ref, loc);
order_ref = Expression::make_cast(unsafe_pointer_type, order_ref, loc);
Expression* count_expr = Expression::make_integer_ul(ncases, int_type, loc);
Expression* send_count_expr = Expression::make_integer_sl(send_count,
int_type,
loc);
Expression* recv_count_expr = Expression::make_integer_sl(recv_count,
int_type,
loc);
Expression* block_expr = Expression::make_boolean(!has_default, loc);
Call_expression* call = Runtime::make_call(Runtime::SELECTGO, loc, 3,
Call_expression* call = Runtime::make_call(Runtime::SELECTGO, loc, 5,
scases_ref, order_ref,
count_expr);
send_count_expr, recv_count_expr,
block_expr);
Expression* result = Expression::make_call_result(call, 0);
Expression* ref = Expression::make_temporary_reference(this->index_, loc);

48
gcc/go/gofrontend/statements.h
View File

@ -1092,6 +1092,9 @@ class Select_clauses
size() const
{ return this->clauses_.size(); }
bool
has_default() const;
// Traverse the select clauses.
int
traverse(Traverse*);
@ -1099,7 +1102,7 @@ class Select_clauses
// Lower statements.
void
lower(Gogo*, Named_object*, Block*, Temporary_statement*,
Temporary_statement*);
Temporary_statement*, int* send_count, int* recv_count);
// Determine types.
void
@ -1138,8 +1141,9 @@ class Select_clauses
Named_object* closedvar, bool is_default, Block* statements,
Location location)
: channel_(channel), val_(val), closed_(closed), var_(var),
closedvar_(closedvar), statements_(statements), location_(location),
is_send_(is_send), is_default_(is_default), is_lowered_(false)
closedvar_(closedvar), statements_(statements), case_index_(0),
location_(location), is_send_(is_send), is_default_(is_default),
is_lowered_(false), is_case_index_set_(false)
{ go_assert(is_default ? channel == NULL : channel != NULL); }
// Traverse the select clause.
@ -1148,7 +1152,7 @@ class Select_clauses
// Lower statements.
void
lower(Gogo*, Named_object*, Block*, Temporary_statement*, size_t,
lower(Gogo*, Named_object*, Block*, Temporary_statement*, int,
Temporary_statement*);
// Determine types.
@ -1210,6 +1214,23 @@ class Select_clauses
location() const
{ return this->location_; }
// Return the case index for this clause.
int
case_index() const
{
go_assert(this->is_case_index_set_);
return this->case_index_;
}
// Set the case index.
void
set_case_index(int i)
{
go_assert(!this->is_case_index_set_);
this->case_index_ = i;
this->is_case_index_set_ = true;
}
// Whether this clause may fall through to the statement which
// follows the overall select statement.
bool
@ -1224,17 +1245,6 @@ class Select_clauses
dump_clause(Ast_dump_context*) const;
private:
// These values must match the values in libgo/go/runtime/select.go.
enum
{
caseRecv = 1,
caseSend = 2,
caseDefault = 3,
};
void
lower_default(Block*, Expression*);
void
lower_send(Block*, Expression*, Expression*);
@ -1243,7 +1253,7 @@ class Select_clauses
Temporary_statement*);
void
set_case(Block*, Expression*, Expression*, Expression*, int);
set_case(Block*, Expression*, Expression*, Expression*);
// The channel.
Expression* channel_;
@ -1259,6 +1269,10 @@ class Select_clauses
Named_object* closedvar_;
// The statements to execute.
Block* statements_;
// The index of this clause in the switch statement. If
// runtime.selectgo returns this index, this clause has been
// chosen.
int case_index_;
// The location of this clause.
Location location_;
// Whether this is a send or a receive.
@ -1267,6 +1281,8 @@ class Select_clauses
bool is_default_;
// Whether this has been lowered.
bool is_lowered_;
// Whether the case index has been set.
bool is_case_index_set_;
};
Select_clause&

7
gcc/go/gofrontend/types.cc
View File

@ -8905,13 +8905,10 @@ Channel_type::select_case_type()
{
Type* unsafe_pointer_type =
Type::make_pointer_type(Type::make_void_type());
Type* uint16_type = Type::lookup_integer_type("uint16");
Type* int64_type = Type::lookup_integer_type("int64");
scase_type =
Type::make_builtin_struct_type(3,
Type::make_builtin_struct_type(2,
"c", unsafe_pointer_type,
"elem", unsafe_pointer_type,
"kind", uint16_type);
"elem", unsafe_pointer_type);
scase_type->set_is_struct_incomparable();
}
return scase_type;

93
libgo/go/runtime/select.go
View File

@ -18,23 +18,12 @@ import (
const debugSelect = false
// scase.kind values.
// Known to compiler.
// Changes here must also be made in src/cmd/compile/internal/gc/select.go's walkselectcases.
const (
caseNil = iota
caseRecv
caseSend
caseDefault
)
// Select case descriptor.
// Known to compiler.
// Changes here must also be made in src/cmd/internal/gc/select.go's scasetype.
type scase struct {
c *hchan // chan
elem unsafe.Pointer // data element
kind uint16
}
func sellock(scases []scase, lockorder []uint16) {
@ -121,7 +110,7 @@ func block() {
// ordinal position of its respective select{recv,send,default} call.
// Also, if the chosen scase was a receive operation, it reports whether
// a value was received.
func selectgo(cas0 *scase, order0 *uint16, ncases int) (int, bool) {
func selectgo(cas0 *scase, order0 *uint16, nsends, nrecvs int, block bool) (int, bool) {
if debugSelect {
print("select: cas0=", cas0, "\n")
}
@ -131,6 +120,7 @@ func selectgo(cas0 *scase, order0 *uint16, ncases int) (int, bool) {
cas1 := (*[1 << 16]scase)(unsafe.Pointer(cas0))
order1 := (*[1 << 17]uint16)(unsafe.Pointer(order0))
ncases := nsends + nrecvs
scases := cas1[:ncases:ncases]
pollorder := order1[:ncases:ncases]
lockorder := order1[ncases:][:ncases:ncases]
@ -154,16 +144,12 @@ func selectgo(cas0 *scase, order0 *uint16, ncases int) (int, bool) {
}
// generate permuted order
dfli := -1
norder := 0
for i := range scases {
cas := &scases[i]
// Omit cases without channels from the poll and lock orders.
if cas.c == nil {
if cas.kind == caseDefault {
dfli = i
}
cas.elem = nil // allow GC
continue
}
@ -246,8 +232,7 @@ func selectgo(cas0 *scase, order0 *uint16, ncases int) (int, bool) {
cas = &scases[casi]
c = cas.c
switch cas.kind {
case caseRecv:
if casi >= nsends {
sg = c.sendq.dequeue()
if sg != nil {
goto recv
@ -258,8 +243,7 @@ func selectgo(cas0 *scase, order0 *uint16, ncases int) (int, bool) {
if c.closed != 0 {
goto rclose
}
case caseSend:
} else {
if c.closed != 0 {
goto sclose
}
@ -273,9 +257,9 @@ func selectgo(cas0 *scase, order0 *uint16, ncases int) (int, bool) {
}
}
if dfli >= 0 {
if !block {
selunlock(scases, lockorder)
casi = dfli
casi = -1
goto retc
}
@ -304,12 +288,10 @@ func selectgo(cas0 *scase, order0 *uint16, ncases int) (int, bool) {
*nextp = sg
nextp = &sg.waitlink
switch cas.kind {
case caseRecv:
c.recvq.enqueue(sg)
case caseSend:
if casi < nsends {
c.sendq.enqueue(sg)
} else {
c.recvq.enqueue(sg)
}
}
@ -357,7 +339,7 @@ func selectgo(cas0 *scase, order0 *uint16, ncases int) (int, bool) {
}
} else {
c = k.c
if k.kind == caseSend {
if int(casei) < nsends {
c.sendq.dequeueSudoG(sglist)
} else {
c.recvq.dequeueSudoG(sglist)
@ -376,13 +358,15 @@ func selectgo(cas0 *scase, order0 *uint16, ncases int) (int, bool) {
c = cas.c
if debugSelect {
print("wait-return: cas0=", cas0, " c=", c, " cas=", cas, " kind=", cas.kind, "\n")
print("wait-return: cas0=", cas0, " c=", c, " cas=", cas, " send=", casi < nsends, "\n")
}
if cas.kind == caseRecv {
if casi < nsends {
if !caseSuccess {
goto sclose
}
} else {
recvOK = caseSuccess
} else if cas.kind == caseSend && !caseSuccess {
goto sclose
}
selunlock(scases, lockorder)
@ -451,7 +435,7 @@ retc:
// Check preemption, since unlike gc we don't check on every call.
// A test case for this one is BenchmarkPingPongHog in proc_test.go.
if dfli >= 0 && getg().preempt {
if block && getg().preempt {
checkPreempt()
}
@ -492,20 +476,49 @@ func reflect_rselect(cases []runtimeSelect) (int, bool) {
block()
}
sel := make([]scase, len(cases))
order := make([]uint16, 2*len(cases))
for i := range cases {
rc := &cases[i]
orig := make([]int, len(cases))
nsends, nrecvs := 0, 0
dflt := -1
for i, rc := range cases {
var j int
switch rc.dir {
case selectDefault:
sel[i] = scase{kind: caseDefault}
dflt = i
continue
case selectSend:
sel[i] = scase{kind: caseSend, c: rc.ch, elem: rc.val}
j = nsends
nsends++
case selectRecv:
sel[i] = scase{kind: caseRecv, c: rc.ch, elem: rc.val}
nrecvs++
j = len(cases) - nrecvs
}
sel[j] = scase{c: rc.ch, elem: rc.val}
orig[j] = i
}
return selectgo(&sel[0], &order[0], len(cases))
// Only a default case.
if nsends+nrecvs == 0 {
return dflt, false
}
// Compact sel and orig if necessary.
if nsends+nrecvs < len(cases) {
copy(sel[nsends:], sel[len(cases)-nrecvs:])
copy(orig[nsends:], orig[len(cases)-nrecvs:])
}
order := make([]uint16, 2*(nsends+nrecvs))
chosen, recvOK := selectgo(&sel[0], &order[0], nsends, nrecvs, dflt == -1)
// Translate chosen back to caller's ordering.
if chosen < 0 {
chosen = dflt
} else {
chosen = orig[chosen]
}
return chosen, recvOK
}
func (q *waitq) dequeueSudoG(sgp *sudog) {