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Commit 83f2c196 authored by kmillikin@chromium.org's avatar kmillikin@chromium.org
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Streamline JumpTarget::ComputeEntryFrame by removing the separate loop 

that sets the static type on elements in the entry frame.  Instead set
the static type as early as possible when computing elements.

Because the elements are shared with the reaching frames, this has the
side effect of sometimes changing the static type of reaching frame
elements.  They will be changed anyway in VirtualFrame::PrepareMergeTo
immediately after, so this is safe.

Review URL: http://codereview.chromium.org/113258

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1928 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
parent 87ebf987
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Showing with 66 additions and 50 deletions
src/jump-target.cc
View file @ 83f2c196
......@@ -101,16 +101,27 @@ FrameElement* JumpTarget::Combine(FrameElement* left, FrameElement* right) {
if (!left->is_valid()) return left;
if (!right->is_valid()) return right;
// If they have the same value, the result is the same. If either
// is unsynced, the result is.
if (left->is_memory() && right->is_memory()) return left;
// If they have the exact same location, the result is in that
// location, otherwise we reallocate. If either is unsynced, the
// result is. The result static type is the merge of the static
// types. It's safe to set it on one of the frame elements, and
// harmless too (because we are only going to merge the reaching
// frames and will ensure that the types are coherent, and changing
// the static type does not emit code).
StaticType type = left->static_type().merge(right->static_type());
if (left->is_memory() && right->is_memory()) {
left->set_static_type(type);
return left;
}
if (left->is_register() && right->is_register() &&
left->reg().is(right->reg())) {
if (!left->is_synced()) {
left->set_static_type(type);
return left;
} else {
right->set_static_type(type);
return right;
}
}
......@@ -119,8 +130,10 @@ FrameElement* JumpTarget::Combine(FrameElement* left, FrameElement* right) {
right->is_constant() &&
left->handle().is_identical_to(right->handle())) {
if (!left->is_synced()) {
left->set_static_type(type);
return left;
} else {
right->set_static_type(type);
return right;
}
}
......@@ -129,8 +142,10 @@ FrameElement* JumpTarget::Combine(FrameElement* left, FrameElement* right) {
right->is_copy() &&
left->index() == right->index()) {
if (!left->is_synced()) {
left->set_static_type(type);
return left;
} else {
right->set_static_type(type);
return right;
}
}
......@@ -165,13 +180,19 @@ void JumpTarget::ComputeEntryFrame(int mergable_elements) {
// frame.
for (int i = 0; i < length; i++) {
FrameElement element = initial_frame->elements_[i];
// We do not allow copies or constants in bidirectional frames.
if (direction_ == BIDIRECTIONAL && i > high_water_mark &&
(element.is_constant() || element.is_copy())) {
elements.Add(NULL);
} else {
elements.Add(&initial_frame->elements_[i]);
// We do not allow copies or constants in bidirectional frames. All
// elements above the water mark on bidirectional frames have
// unknown static types.
if (direction_ == BIDIRECTIONAL && i > high_water_mark) {
if (element.is_constant() || element.is_copy()) {
elements.Add(NULL);
continue;
}
// It's safe to change the static type on the initial frame
// element, see comment in JumpTarget::Combine.
initial_frame->elements_[i].set_static_type(StaticType::unknown());
}
elements.Add(&initial_frame->elements_[i]);
}
// Compute elements based on the other reaching frames.
......@@ -229,36 +250,45 @@ void JumpTarget::ComputeEntryFrame(int mergable_elements) {
// memory, from the top down.
for (int i = length - 1; i >= 0; i--) {
if (elements[i] == NULL) {
// If the value is synced on all frames, put it in memory. This
// costs nothing at the merge code but will incur a
// memory-to-register move when the value is needed later.
// Loop over all the reaching frames to check whether the element
// is synced on all frames, to count the registers it occupies,
// and to compute a merged static type.
bool is_synced = true;
for (int j = 0; is_synced && j < reaching_frames_.length(); j++) {
is_synced = reaching_frames_[j]->elements_[i].is_synced();
}
// There is nothing to be done if the elements are all synced.
// It is already recorded as a memory element.
if (is_synced) continue;
// Choose an available register. Prefer ones that the element
// is already occupying on some reaching frame.
RegisterFile candidate_registers;
int max_count = kMinInt;
int best_count = kMinInt;
int best_reg_code = no_reg.code_;
StaticType type; // Initially invalid.
if (direction_ != BIDIRECTIONAL || i < high_water_mark) {
type = reaching_frames_[0]->elements_[i].static_type();
}
for (int j = 0; j < reaching_frames_.length(); j++) {
FrameElement element = reaching_frames_[j]->elements_[i];
if (element.is_register() &&
!entry_frame_->is_used(element.reg())) {
is_synced = is_synced && element.is_synced();
if (element.is_register() && !entry_frame_->is_used(element.reg())) {
// Count the register occurrence and remember it if better
// than the previous best.
candidate_registers.Use(element.reg());
if (candidate_registers.count(element.reg()) > max_count) {
max_count = candidate_registers.count(element.reg());
if (candidate_registers.count(element.reg()) > best_count) {
best_count = candidate_registers.count(element.reg());
best_reg_code = element.reg().code();
}
}
type = type.merge(element.static_type());
}
// If there was no preferred choice consider any free register.
// If the value is synced on all frames, put it in memory. This
// costs nothing at the merge code but will incur a
// memory-to-register move when the value is needed later.
if (is_synced) {
// Already recorded as a memory element.
entry_frame_->elements_[i].set_static_type(type);
continue;
}
// Try to put it in a register. If there was no best choice
// consider any free register.
if (best_reg_code == no_reg.code_) {
for (int j = 0; j < kNumRegisters; j++) {
if (!entry_frame_->is_used(j) && !RegisterAllocator::IsReserved(j)) {
......@@ -268,36 +298,22 @@ void JumpTarget::ComputeEntryFrame(int mergable_elements) {
}
}
if (best_reg_code != no_reg.code_) {
if (best_reg_code == no_reg.code_) {
// If there was no register found, the element is already
// recorded as in memory.
entry_frame_->elements_[i].set_static_type(type);
} else {
// If there was a register choice, use it. Preserve the copied
// flag on the element.
// flag on the element. Set the static type as computed.
bool is_copied = entry_frame_->elements_[i].is_copied();
Register reg = { best_reg_code };
entry_frame_->elements_[i] =
FrameElement::RegisterElement(reg,
FrameElement::NOT_SYNCED);
if (is_copied) entry_frame_->elements_[i].set_copied();
entry_frame_->elements_[i].set_static_type(type);
entry_frame_->register_locations_[best_reg_code] = i;
}
// If there was no register found, the element is already
// recorded as in memory.
}
}
// Set the static type of frame elements.
for (int i = 0; i < length; i++) {
FrameElement* current = &entry_frame_->elements_[i];
if (direction_ == BIDIRECTIONAL && i >= high_water_mark) {
current->set_static_type(StaticType::unknown());
} else {
StaticType merged_type = reaching_frames_[0]->elements_[i].static_type();
for (int j = 1, n = reaching_frames_.length();
!merged_type.is_unknown() && j < n;
j++) {
merged_type =
merged_type.merge(reaching_frames_[j]->elements_[i].static_type());
}
current->set_static_type(merged_type);
}
}
......
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