From 313890530c53475f2b76c4cae0d69b9b73de648c Mon Sep 17 00:00:00 2001 From: Ian Lance Taylor Date: Tue, 22 Dec 2020 11:04:35 -0800 Subject: [PATCH] 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. Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/279735 --- gcc/go/gofrontend/MERGE | 2 +- gcc/go/gofrontend/runtime.def | 4 +- gcc/go/gofrontend/statements.cc | 131 ++++++++++++++++++++++---------- gcc/go/gofrontend/statements.h | 48 ++++++++---- gcc/go/gofrontend/types.cc | 7 +- libgo/go/runtime/select.go | 93 +++++++++++++---------- 6 files changed, 182 insertions(+), 103 deletions(-) diff --git a/gcc/go/gofrontend/MERGE b/gcc/go/gofrontend/MERGE index bb537f152b9..c70b60c657f 100644 --- a/gcc/go/gofrontend/MERGE +++ b/gcc/go/gofrontend/MERGE @@ -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. diff --git a/gcc/go/gofrontend/runtime.def b/gcc/go/gofrontend/runtime.def index 4b606a6c00c..7ab94a3ffbc 100644 --- a/gcc/go/gofrontend/runtime.def +++ b/gcc/go/gofrontend/runtime.def @@ -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. diff --git a/gcc/go/gofrontend/statements.cc b/gcc/go/gofrontend/statements.cc index 398b8fd82f2..da0e0843a73 100644 --- a/gcc/go/gofrontend/statements.cc +++ b/gcc/go/gofrontend/statements.cc @@ -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(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); diff --git a/gcc/go/gofrontend/statements.h b/gcc/go/gofrontend/statements.h index 47092b4912a..c08b493e6c9 100644 --- a/gcc/go/gofrontend/statements.h +++ b/gcc/go/gofrontend/statements.h @@ -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& diff --git a/gcc/go/gofrontend/types.cc b/gcc/go/gofrontend/types.cc index 12e783010db..16f0eb59a50 100644 --- a/gcc/go/gofrontend/types.cc +++ b/gcc/go/gofrontend/types.cc @@ -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; diff --git a/libgo/go/runtime/select.go b/libgo/go/runtime/select.go index c31aa344b55..45cc2847945 100644 --- a/libgo/go/runtime/select.go +++ b/libgo/go/runtime/select.go @@ -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) {