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8341293: Split field loads through Nested Phis #21270

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8341293: Split field loads through Nested Phis #21270

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7957937
Split load fields through nestead phi nodes
dhanalla Sep 30, 2024
a209800
Fix trailing whitespaces
dhanalla Sep 30, 2024
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101 changes: 70 additions & 31 deletions src/hotspot/share/opto/escape.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -463,8 +463,15 @@ bool ConnectionGraph::compute_escape() {
// if at least one scalar replaceable allocation participates in the merge.
bool ConnectionGraph::can_reduce_phi_check_inputs(PhiNode* ophi) const {
bool found_sr_allocate = false;

int nof_input_phi_nodes = 0;
for (uint i = 1; i < ophi->req(); i++) {
if (ophi->in(i)->is_Phi()) {
// ignore phi node with more than one input phi node
if (++nof_input_phi_nodes > 1) {
NOT_PRODUCT(if (TraceReduceAllocationMerges) tty->print_cr("Cannot reduce Phi %d. More than one input phi node.", ophi->_idx);)
return false;
}
}
JavaObjectNode* ptn = unique_java_object(ophi->in(i));
if (ptn != nullptr && ptn->scalar_replaceable()) {
AllocateNode* alloc = ptn->ideal_node()->as_Allocate();
Expand All @@ -484,7 +491,7 @@ bool ConnectionGraph::can_reduce_phi_check_inputs(PhiNode* ophi) const {
}
}

NOT_PRODUCT(if (TraceReduceAllocationMerges && !found_sr_allocate) tty->print_cr("Can NOT reduce Phi %d on invocation %d. No SR Allocate as input.", ophi->_idx, _invocation);)
NOT_PRODUCT(if (TraceReduceAllocationMerges && !found_sr_allocate) tty->print_cr("Cannot reduce Phi %d on invocation %d. No SR Allocate as input.", ophi->_idx, _invocation);)
return found_sr_allocate;
}

Expand Down Expand Up @@ -527,41 +534,50 @@ bool ConnectionGraph::has_been_reduced(PhiNode* n, SafePointNode* sfpt) const {
// - Phi -> AddP -> Load
// - Phi -> CastPP -> SafePoints
// - Phi -> CastPP -> AddP -> Load
bool ConnectionGraph::can_reduce_check_users(Node* n, uint nesting) const {
// - Phi -> Phi -> AddP -> Load
bool ConnectionGraph::can_reduce_check_users(Node* n, uint phi_nest_level) const {
for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax; i++) {
Node* use = n->fast_out(i);

if (use->is_SafePoint()) {
// Skip Phi -> Phi -> SafePoints and allow only Phi -> SafePoints and Phi -> CastPP -> SafePoints
if (use->is_SafePoint() && (!n->is_Phi() || phi_nest_level < 1)) {
if (use->is_Call() && use->as_Call()->has_non_debug_use(n)) {
NOT_PRODUCT(if (TraceReduceAllocationMerges) tty->print_cr("Can NOT reduce Phi %d on invocation %d. Call has non_debug_use().", n->_idx, _invocation);)
NOT_PRODUCT(if (TraceReduceAllocationMerges) tty->print_cr("Cannot reduce Phi %d on invocation %d. Call has non_debug_use().", n->_idx, _invocation);)
return false;
} else if (has_been_reduced(n->is_Phi() ? n->as_Phi() : n->as_CastPP()->in(1)->as_Phi(), use->as_SafePoint())) {
NOT_PRODUCT(if (TraceReduceAllocationMerges) tty->print_cr("Can NOT reduce Phi %d on invocation %d. It has already been reduced.", n->_idx, _invocation);)
NOT_PRODUCT(if (TraceReduceAllocationMerges) tty->print_cr("Cannot reduce Phi %d on invocation %d. It has already been reduced.", n->_idx, _invocation);)
return false;
}
} else if (use->is_AddP()) {
assert(phi_nest_level <= 1, "unexpected nesting level");
Node* addp = use;
for (DUIterator_Fast jmax, j = addp->fast_outs(jmax); j < jmax; j++) {
Node* use_use = addp->fast_out(j);
const Type* load_type = _igvn->type(use_use);

if (!use_use->is_Load() || !use_use->as_Load()->can_split_through_phi_base(_igvn)) {
NOT_PRODUCT(if (TraceReduceAllocationMerges) tty->print_cr("Can NOT reduce Phi %d on invocation %d. AddP user isn't a [splittable] Load(): %s", n->_idx, _invocation, use_use->Name());)
if (!use_use->is_Load() || !use_use->as_Load()->can_split_through_phi_base(_igvn, (phi_nest_level > 0))) {
NOT_PRODUCT(if (TraceReduceAllocationMerges) tty->print_cr("Cannot reduce %s Phi %d on invocation %d. AddP user isn't a [splittable] Load(): %s", (phi_nest_level > 0)?"nested":"", n->_idx, _invocation, use_use->Name());)
return false;
} else if (load_type->isa_narrowklass() || load_type->isa_klassptr()) {
NOT_PRODUCT(if (TraceReduceAllocationMerges) tty->print_cr("Can NOT reduce Phi %d on invocation %d. [Narrow] Klass Load: %s", n->_idx, _invocation, use_use->Name());)
NOT_PRODUCT(if (TraceReduceAllocationMerges) tty->print_cr("Cannot reduce %s Phi %d on invocation %d. [Narrow] Klass Load: %s", (phi_nest_level > 0)?"nested":"", n->_idx, _invocation, use_use->Name());)
return false;
}
}
} else if (nesting > 0) {
NOT_PRODUCT(if (TraceReduceAllocationMerges) tty->print_cr("Can NOT reduce Phi %d on invocation %d. Unsupported user %s at nesting level %d.", n->_idx, _invocation, use->Name(), nesting);)
} else if (phi_nest_level > 0) {
NOT_PRODUCT(if (TraceReduceAllocationMerges) tty->print_cr("Cannot reduce Phi %d on invocation %d. Unsupported user %s at nesting level %d.", n->_idx, _invocation, use->Name(), phi_nest_level);)
return false;
} else if (use->is_Phi()) {
if (n->_idx == use->_idx) {
NOT_PRODUCT(if (TraceReduceAllocationMerges) tty->print_cr("Cannot reduce Self loop nested Phi");)
return false;
} else if (!can_reduce_phi_check_inputs(use->as_Phi()) || !can_reduce_check_users(use->as_Phi(), phi_nest_level+1)) {
return false;
}
} else if (use->is_CastPP()) {
const Type* cast_t = _igvn->type(use);
if (cast_t == nullptr || cast_t->make_ptr()->isa_instptr() == nullptr) {
#ifndef PRODUCT
if (TraceReduceAllocationMerges) {
tty->print_cr("Can NOT reduce Phi %d on invocation %d. CastPP is not to an instance.", n->_idx, _invocation);
tty->print_cr("Cannot reduce Phi %d on invocation %d. CastPP is not to an instance.", n->_idx, _invocation);
use->dump();
}
#endif
Expand All @@ -586,7 +602,7 @@ bool ConnectionGraph::can_reduce_check_users(Node* n, uint nesting) const {
if (!can_reduce) {
#ifndef PRODUCT
if (TraceReduceAllocationMerges) {
tty->print_cr("Can NOT reduce Phi %d on invocation %d. CastPP %d doesn't have simple control.", n->_idx, _invocation, use->_idx);
tty->print_cr("Cannot reduce Phi %d on invocation %d. CastPP %d doesn't have simple control.", n->_idx, _invocation, use->_idx);
n->dump(5);
}
#endif
Expand All @@ -595,16 +611,16 @@ bool ConnectionGraph::can_reduce_check_users(Node* n, uint nesting) const {
}
}

if (!can_reduce_check_users(use, nesting+1)) {
if (!can_reduce_check_users(use, phi_nest_level+1)) {
return false;
}
} else if (use->Opcode() == Op_CmpP || use->Opcode() == Op_CmpN) {
if (!can_reduce_cmp(n, use)) {
NOT_PRODUCT(if (TraceReduceAllocationMerges) tty->print_cr("Can NOT reduce Phi %d on invocation %d. CmpP/N %d isn't reducible.", n->_idx, _invocation, use->_idx);)
NOT_PRODUCT(if (TraceReduceAllocationMerges) tty->print_cr("Cannot reduce Phi %d on invocation %d. CmpP/N %d isn't reducible.", n->_idx, _invocation, use->_idx);)
return false;
}
} else {
NOT_PRODUCT(if (TraceReduceAllocationMerges) tty->print_cr("Can NOT reduce Phi %d on invocation %d. One of the uses is: %d %s", n->_idx, _invocation, use->_idx, use->Name());)
NOT_PRODUCT(if (TraceReduceAllocationMerges) tty->print_cr("Cannot reduce Phi %d on invocation %d. One of the uses is: %d %s", n->_idx, _invocation, use->_idx, use->Name());)
return false;
}
}
Expand All @@ -631,7 +647,7 @@ bool ConnectionGraph::can_reduce_phi(PhiNode* ophi) const {
return false;
}

if (!can_reduce_phi_check_inputs(ophi) || !can_reduce_check_users(ophi, /* nesting: */ 0)) {
if (!can_reduce_phi_check_inputs(ophi) || !can_reduce_check_users(ophi, /* phi_nest_level: */ 0)) {
return false;
}

Expand Down Expand Up @@ -738,7 +754,7 @@ Node* ConnectionGraph::specialize_castpp(Node* castpp, Node* base, Node* current
return _igvn->transform(ConstraintCastNode::make_cast_for_type(not_eq_control, base, _igvn->type(castpp), ConstraintCastNode::UnconditionalDependency, nullptr));
}

Node* ConnectionGraph::split_castpp_load_through_phi(Node* curr_addp, Node* curr_load, Node* region, GrowableArray<Node*>* bases_for_loads, GrowableArray<Node *> &alloc_worklist) {
Node* ConnectionGraph::split_castpp_load_through_phi(Node* curr_addp, Node* curr_load, Node* region, GrowableArray<Node*>* bases_for_loads, GrowableArray<Node *> &alloc_worklist, Unique_Node_List &reducible_merges) {
const Type* load_type = _igvn->type(curr_load);
Node* nsr_value = _igvn->zerocon(load_type->basic_type());
Node* memory = curr_load->in(MemNode::Memory);
Expand Down Expand Up @@ -788,7 +804,7 @@ Node* ConnectionGraph::split_castpp_load_through_phi(Node* curr_addp, Node* curr

// Takes care of updating CG and split_unique_types worklists due
// to cloned AddP->Load.
updates_after_load_split(data_phi, curr_load, alloc_worklist);
updates_after_load_split(data_phi, curr_load, alloc_worklist, reducible_merges);

return _igvn->transform(data_phi);
}
Expand Down Expand Up @@ -865,7 +881,7 @@ Node* ConnectionGraph::split_castpp_load_through_phi(Node* curr_addp, Node* curr
// \|/
// Phi # "Field" Phi
//
void ConnectionGraph::reduce_phi_on_castpp_field_load(Node* curr_castpp, GrowableArray<Node *> &alloc_worklist, GrowableArray<Node *> &memnode_worklist) {
void ConnectionGraph::reduce_phi_on_castpp_field_load(Node* curr_castpp, GrowableArray<Node *> &alloc_worklist, GrowableArray<Node *> &memnode_worklist, Unique_Node_List &reducible_merges) {
Node* ophi = curr_castpp->in(1);
assert(ophi->is_Phi(), "Expected this to be a Phi node.");

Expand Down Expand Up @@ -913,7 +929,7 @@ void ConnectionGraph::reduce_phi_on_castpp_field_load(Node* curr_castpp, Growabl
// 'split_castpp_load_through_phi` method will add an
// 'If-Then-Else-Region` around nullable bases and only load from them
// when the input is not null.
Node* phi = split_castpp_load_through_phi(use, use_use, ophi->in(0), &bases_for_loads, alloc_worklist);
Node* phi = split_castpp_load_through_phi(use, use_use, ophi->in(0), &bases_for_loads, alloc_worklist, reducible_merges);
_igvn->replace_node(use_use, phi);

--j;
Expand Down Expand Up @@ -1014,7 +1030,7 @@ void ConnectionGraph::reduce_phi_on_cmp(Node* cmp) {
// the connection graph. Note that the changes in the CG below
// won't affect the ES of objects since the new nodes have the
// same status as the old ones.
void ConnectionGraph::updates_after_load_split(Node* data_phi, Node* previous_load, GrowableArray<Node *> &alloc_worklist) {
void ConnectionGraph::updates_after_load_split(Node* data_phi, Node* previous_load, GrowableArray<Node *> &alloc_worklist, Unique_Node_List &reducible_merges) {
assert(data_phi != nullptr, "Output of split_through_phi is null.");
assert(data_phi != previous_load, "Output of split_through_phi is same as input.");
assert(data_phi->is_Phi(), "Output of split_through_phi isn't a Phi.");
Expand Down Expand Up @@ -1043,8 +1059,14 @@ void ConnectionGraph::updates_after_load_split(Node* data_phi, Node* previous_lo
// The base might not be something that we can create an unique
// type for. If that's the case we are done with that input.
PointsToNode* jobj_ptn = unique_java_object(base);
if (jobj_ptn == nullptr || !jobj_ptn->scalar_replaceable()) {
continue;
if (base->is_Phi()) {
if (!reducible_merges.member(base)) {
continue;
}
} else {
if (jobj_ptn == nullptr || !jobj_ptn->scalar_replaceable()) {
continue;
}
}

// Push to alloc_worklist since the base has an unique_type
Expand All @@ -1067,7 +1089,7 @@ void ConnectionGraph::updates_after_load_split(Node* data_phi, Node* previous_lo
}
}

void ConnectionGraph::reduce_phi_on_field_access(Node* previous_addp, GrowableArray<Node *> &alloc_worklist) {
void ConnectionGraph::reduce_phi_on_field_access(Node* previous_addp, GrowableArray<Node *> &alloc_worklist, Unique_Node_List &reducible_merges) {
// We'll pass this to 'split_through_phi' so that it'll do the split even
// though the load doesn't have an unique instance type.
bool ignore_missing_instance_id = true;
Expand All @@ -1083,7 +1105,7 @@ void ConnectionGraph::reduce_phi_on_field_access(Node* previous_addp, GrowableAr

// Takes care of updating CG and split_unique_types worklists due to cloned
// AddP->Load.
updates_after_load_split(data_phi, previous_load, alloc_worklist);
updates_after_load_split(data_phi, previous_load, alloc_worklist, reducible_merges);

_igvn->replace_node(previous_load, data_phi);
}
Expand Down Expand Up @@ -1274,7 +1296,24 @@ bool ConnectionGraph::reduce_phi_on_safepoints_helper(Node* ophi, Node* cast, No
return true;
}

void ConnectionGraph::reduce_phi(PhiNode* ophi, GrowableArray<Node *> &alloc_worklist, GrowableArray<Node *> &memnode_worklist) {
void ConnectionGraph::reduce_phi(PhiNode* ophi, GrowableArray<Node *> &alloc_worklist, GrowableArray<Node *> &memnode_worklist, Unique_Node_List &reducible_merges) {
Unique_Node_List nested_phis;
// Collect nested phi nodes first because the graph will change while splitting the child/nested phi node.
for (DUIterator_Fast imax, i = ophi->fast_outs(imax); i < imax; i++) {
Node* use = ophi->fast_out(i);
if (use->is_Phi()) {
assert(use->_idx != ophi->_idx, "Unexpected selfloop Phi.");
nested_phis.push(use);
}
}

// Splitting through the child phi nodes ahead of parent phi nodes in nested scenarios is crucial.
// Ensure that the splits are applied to the load fields of child phi nodes before the parent phi nodes take place.
for (uint i = 0; i < nested_phis.size(); i++) {
Node *nested_phi = nested_phis.at(i);
reduce_phi(nested_phi->as_Phi(), alloc_worklist, memnode_worklist, reducible_merges);
}

bool delay = _igvn->delay_transform();
_igvn->set_delay_transform(true);
_igvn->hash_delete(ophi);
Expand Down Expand Up @@ -1302,14 +1341,14 @@ void ConnectionGraph::reduce_phi(PhiNode* ophi, GrowableArray<Node *> &alloc_wo
// splitting CastPPs we make reference to the inputs of the Cmp that is used
// by the If controlling the CastPP.
for (uint i = 0; i < castpps.size(); i++) {
reduce_phi_on_castpp_field_load(castpps.at(i), alloc_worklist, memnode_worklist);
reduce_phi_on_castpp_field_load(castpps.at(i), alloc_worklist, memnode_worklist, reducible_merges);
}

for (uint i = 0; i < others.size(); i++) {
Node* use = others.at(i);

if (use->is_AddP()) {
reduce_phi_on_field_access(use, alloc_worklist);
reduce_phi_on_field_access(use, alloc_worklist, reducible_merges);
} else if(use->is_Cmp()) {
reduce_phi_on_cmp(use);
}
Expand Down Expand Up @@ -4461,7 +4500,7 @@ void ConnectionGraph::split_unique_types(GrowableArray<Node *> &alloc_worklist,
// finishes. For now we just try to split out the SR inputs of the merge.
Node* parent = n->in(1);
if (reducible_merges.member(n)) {
reduce_phi(n->as_Phi(), alloc_worklist, memnode_worklist);
reduce_phi(n->as_Phi(), alloc_worklist, memnode_worklist, reducible_merges);
#ifdef ASSERT
if (VerifyReduceAllocationMerges) {
reduced_merges.push(n);
Expand Down
12 changes: 6 additions & 6 deletions src/hotspot/share/opto/escape.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -592,8 +592,8 @@ class ConnectionGraph: public ArenaObj {
// Methods related to Reduce Allocation Merges
bool has_non_reducible_merge(FieldNode* field, Unique_Node_List& reducible_merges);
PhiNode* create_selector(PhiNode* ophi) const;
void updates_after_load_split(Node* data_phi, Node* previous_load, GrowableArray<Node *> &alloc_worklist);
Node* split_castpp_load_through_phi(Node* curr_addp, Node* curr_load, Node* region, GrowableArray<Node*>* bases_for_loads, GrowableArray<Node *> &alloc_worklist);
void updates_after_load_split(Node* data_phi, Node* previous_load, GrowableArray<Node *> &alloc_worklist, Unique_Node_List &reducible_merges);
Node* split_castpp_load_through_phi(Node* curr_addp, Node* curr_load, Node* region, GrowableArray<Node*>* bases_for_loads, GrowableArray<Node *> &alloc_worklist, Unique_Node_List &reducible_merges);
void reset_scalar_replaceable_entries(PhiNode* ophi);
bool has_reducible_merge_base(AddPNode* n, Unique_Node_List &reducible_merges);
Node* specialize_cmp(Node* base, Node* curr_ctrl);
Expand All @@ -602,15 +602,15 @@ class ConnectionGraph: public ArenaObj {
bool can_reduce_cmp(Node* n, Node* cmp) const;
bool has_been_reduced(PhiNode* n, SafePointNode* sfpt) const;
bool can_reduce_phi(PhiNode* ophi) const;
bool can_reduce_check_users(Node* n, uint nesting) const;
bool can_reduce_check_users(Node* n, uint phi_nest_level) const;
bool can_reduce_phi_check_inputs(PhiNode* ophi) const;

void reduce_phi_on_field_access(Node* previous_addp, GrowableArray<Node *> &alloc_worklist);
void reduce_phi_on_castpp_field_load(Node* castpp, GrowableArray<Node *> &alloc_worklist, GrowableArray<Node *> &memnode_worklist);
void reduce_phi_on_field_access(Node* previous_addp, GrowableArray<Node *> &alloc_worklist, Unique_Node_List &reducible_merges);
void reduce_phi_on_castpp_field_load(Node* castpp, GrowableArray<Node *> &alloc_worklist, GrowableArray<Node *> &memnode_worklist, Unique_Node_List &reducible_merges);
void reduce_phi_on_cmp(Node* cmp);
bool reduce_phi_on_safepoints(PhiNode* ophi);
bool reduce_phi_on_safepoints_helper(Node* ophi, Node* cast, Node* selector, Unique_Node_List& safepoints);
void reduce_phi(PhiNode* ophi, GrowableArray<Node *> &alloc_worklist, GrowableArray<Node *> &memnode_worklist);
void reduce_phi(PhiNode* ophi, GrowableArray<Node *> &alloc_worklist, GrowableArray<Node *> &memnode_worklist, Unique_Node_List &reducible_merges);

void set_not_scalar_replaceable(PointsToNode* ptn NOT_PRODUCT(COMMA const char* reason)) const {
#ifndef PRODUCT
Expand Down
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