ART: Add div-zero check elimination to LVN/GVN
GVN has been updated to also consider div/rem zero check elimination.
This means that whenever a divisor is used in two sequential divisions,
the second division will surely not throw exception.
The algorithm has been updated to work on global level by considering
splits and merges. Obviously, if "div_zero" checked on one path but
not the other, at merge point consider that division has not been
eliminated.
One big deficiency of this algorithm is that it does not consider
literals in the divisor. Namely, in cases where the operand is a literal
or a constant (literal created by another bytecode), it does not mark as
divide by zero checked. However, in reality this is not an issue
because none of the backends generate the divide by zero check when
the constant value is known.
Issue: CAR-868
Category: device enablement
Domain: AOSP.ART-ME
Origin: internal
Upstream-Candidate: yes
Change-Id: I617569055c73a45e13e2a83392b99b48f4e33362
Signed-off-by: Razvan A Lupusoru <razvan.a.lupusoru@intel.com>
diff --git a/compiler/dex/local_value_numbering.cc b/compiler/dex/local_value_numbering.cc
index c1ce2ac..854759b 100644
--- a/compiler/dex/local_value_numbering.cc
+++ b/compiler/dex/local_value_numbering.cc
@@ -339,6 +339,7 @@
escaped_array_clobber_set_(EscapedArrayClobberKeyComparator(), allocator->Adapter()),
range_checked_(RangeCheckKeyComparator() , allocator->Adapter()),
null_checked_(std::less<uint16_t>(), allocator->Adapter()),
+ div_zero_checked_(std::less<uint16_t>(), allocator->Adapter()),
merge_names_(allocator->Adapter()),
merge_map_(std::less<ScopedArenaVector<BasicBlockId>>(), allocator->Adapter()),
merge_new_memory_version_(kNoValue) {
@@ -362,7 +363,8 @@
escaped_ifield_clobber_set_ == other.escaped_ifield_clobber_set_ &&
escaped_array_clobber_set_ == other.escaped_array_clobber_set_ &&
range_checked_ == other.range_checked_ &&
- null_checked_ == other.null_checked_;
+ null_checked_ == other.null_checked_ &&
+ div_zero_checked_ == other.div_zero_checked_;
}
void LocalValueNumbering::MergeOne(const LocalValueNumbering& other, MergeType merge_type) {
@@ -379,6 +381,7 @@
non_aliasing_refs_ = other.non_aliasing_refs_;
range_checked_ = other.range_checked_;
null_checked_ = other.null_checked_;
+ div_zero_checked_ = other.div_zero_checked_;
const BasicBlock* pred_bb = gvn_->GetBasicBlock(other.Id());
if (GlobalValueNumbering::HasNullCheckLastInsn(pred_bb, Id())) {
@@ -699,6 +702,28 @@
}
}
+void LocalValueNumbering::MergeDivZeroChecked() {
+ DCHECK_GE(gvn_->merge_lvns_.size(), 2u);
+
+ // Find the LVN with the least entries in the set.
+ const LocalValueNumbering* least_entries_lvn = gvn_->merge_lvns_[0];
+ for (const LocalValueNumbering* lvn : gvn_->merge_lvns_) {
+ if (lvn->div_zero_checked_.size() < least_entries_lvn->div_zero_checked_.size()) {
+ least_entries_lvn = lvn;
+ }
+ }
+
+ // For each div-zero value name check if it's div-zero checked in all the LVNs.
+ for (const auto& value_name : least_entries_lvn->div_zero_checked_) {
+ // Merge null_checked_ for this ref.
+ merge_names_.clear();
+ merge_names_.resize(gvn_->merge_lvns_.size(), value_name);
+ if (gvn_->DivZeroCheckedInAllPredecessors(merge_names_)) {
+ div_zero_checked_.insert(div_zero_checked_.end(), value_name);
+ }
+ }
+}
+
void LocalValueNumbering::MergeSFieldValues(const SFieldToValueMap::value_type& entry,
SFieldToValueMap::iterator hint) {
uint16_t field_id = entry.first;
@@ -931,6 +956,9 @@
// Merge null_checked_. We may later insert more, such as merged object field values.
MergeNullChecked();
+ // Now merge the div_zero_checked_.
+ MergeDivZeroChecked();
+
if (merge_type == kCatchMerge) {
// Memory is clobbered. New memory version already created, don't merge aliasing locations.
return;
@@ -1054,6 +1082,20 @@
}
}
+void LocalValueNumbering::HandleDivZeroCheck(MIR* mir, uint16_t reg) {
+ auto lb = div_zero_checked_.lower_bound(reg);
+ if (lb != div_zero_checked_.end() && *lb == reg) {
+ if (LIKELY(gvn_->CanModify())) {
+ if (gvn_->GetCompilationUnit()->verbose) {
+ LOG(INFO) << "Removing div zero check for 0x" << std::hex << mir->offset;
+ }
+ mir->optimization_flags |= MIR_IGNORE_DIV_ZERO_CHECK;
+ }
+ } else {
+ div_zero_checked_.insert(lb, reg);
+ }
+}
+
void LocalValueNumbering::HandlePutObject(MIR* mir) {
// If we're storing a non-aliasing reference, stop tracking it as non-aliasing now.
uint16_t base = GetOperandValue(mir->ssa_rep->uses[0]);
@@ -1139,6 +1181,9 @@
if (!wide && gvn_->NullCheckedInAllPredecessors(merge_names_)) {
null_checked_.insert(value_name);
}
+ if (gvn_->DivZeroCheckedInAllPredecessors(merge_names_)) {
+ div_zero_checked_.insert(value_name);
+ }
}
}
if (wide) {
@@ -1696,6 +1741,13 @@
}
break;
+ case Instruction::DIV_INT:
+ case Instruction::DIV_INT_2ADDR:
+ case Instruction::REM_INT:
+ case Instruction::REM_INT_2ADDR:
+ HandleDivZeroCheck(mir, GetOperandValue(mir->ssa_rep->uses[1]));
+ FALLTHROUGH_INTENDED;
+
case Instruction::CMPG_FLOAT:
case Instruction::CMPL_FLOAT:
case Instruction::ADD_INT:
@@ -1710,10 +1762,6 @@
case Instruction::XOR_INT_2ADDR:
case Instruction::SUB_INT:
case Instruction::SUB_INT_2ADDR:
- case Instruction::DIV_INT:
- case Instruction::DIV_INT_2ADDR:
- case Instruction::REM_INT:
- case Instruction::REM_INT_2ADDR:
case Instruction::SHL_INT:
case Instruction::SHL_INT_2ADDR:
case Instruction::SHR_INT:
@@ -1728,19 +1776,22 @@
}
break;
+ case Instruction::DIV_LONG:
+ case Instruction::REM_LONG:
+ case Instruction::DIV_LONG_2ADDR:
+ case Instruction::REM_LONG_2ADDR:
+ HandleDivZeroCheck(mir, GetOperandValueWide(mir->ssa_rep->uses[2]));
+ FALLTHROUGH_INTENDED;
+
case Instruction::ADD_LONG:
case Instruction::SUB_LONG:
case Instruction::MUL_LONG:
- case Instruction::DIV_LONG:
- case Instruction::REM_LONG:
case Instruction::AND_LONG:
case Instruction::OR_LONG:
case Instruction::XOR_LONG:
case Instruction::ADD_LONG_2ADDR:
case Instruction::SUB_LONG_2ADDR:
case Instruction::MUL_LONG_2ADDR:
- case Instruction::DIV_LONG_2ADDR:
- case Instruction::REM_LONG_2ADDR:
case Instruction::AND_LONG_2ADDR:
case Instruction::OR_LONG_2ADDR:
case Instruction::XOR_LONG_2ADDR: