runtime: eliminate scase.kind field
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.
Change-Id: I39a0a83c25e15fbd3cdfac7f31e01df9f2cddd3f
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/279735
Trust: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
diff --git a/go/runtime.def b/go/runtime.def
index 4b606a6..7ab94a3 100644
--- a/go/runtime.def
+++ b/go/runtime.def
@@ -195,8 +195,8 @@
// 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.
diff --git a/go/statements.cc b/go/statements.cc
index 398b8fd..da0e084 100644
--- a/go/statements.cc
+++ b/go/statements.cc
@@ -5291,22 +5291,23 @@
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 @@
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 @@
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 @@
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 @@
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 @@
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 @@
// 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 @@
// 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 @@
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 @@
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 @@
// 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 @@
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 @@
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);
diff --git a/go/statements.h b/go/statements.h
index 47092b4..c08b493 100644
--- a/go/statements.h
+++ b/go/statements.h
@@ -1092,6 +1092,9 @@
size() const
{ return this->clauses_.size(); }
+ bool
+ has_default() const;
+
// Traverse the select clauses.
int
traverse(Traverse*);
@@ -1099,7 +1102,7 @@
// 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 @@
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 @@
// 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 @@
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 @@
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 @@
Temporary_statement*);
void
- set_case(Block*, Expression*, Expression*, Expression*, int);
+ set_case(Block*, Expression*, Expression*, Expression*);
// The channel.
Expression* channel_;
@@ -1259,6 +1269,10 @@
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 @@
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&
diff --git a/go/types.cc b/go/types.cc
index 12e7830..16f0eb5 100644
--- a/go/types.cc
+++ b/go/types.cc
@@ -8905,13 +8905,10 @@
{
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;
diff --git a/libgo/go/runtime/select.go b/libgo/go/runtime/select.go
index c31aa34..45cc284 100644
--- a/libgo/go/runtime/select.go
+++ b/libgo/go/runtime/select.go
@@ -18,23 +18,12 @@
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 @@
// 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 @@
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 @@
}
// 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 @@
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 @@
if c.closed != 0 {
goto rclose
}
-
- case caseSend:
+ } else {
if c.closed != 0 {
goto sclose
}
@@ -273,9 +257,9 @@
}
}
- if dfli >= 0 {
+ if !block {
selunlock(scases, lockorder)
- casi = dfli
+ casi = -1
goto retc
}
@@ -304,12 +288,10 @@
*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 @@
}
} 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 @@
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 @@
// 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 @@
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) {
