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.h b/compiler/dex/local_value_numbering.h
index 979fd5a..8613f97 100644
--- a/compiler/dex/local_value_numbering.h
+++ b/compiler/dex/local_value_numbering.h
@@ -47,6 +47,10 @@
return null_checked_.find(value_name) != null_checked_.end();
}
+ bool IsValueDivZeroChecked(uint16_t value_name) const {
+ return div_zero_checked_.find(value_name) != div_zero_checked_.end();
+ }
+
bool IsSregValue(uint16_t s_reg, uint16_t value_name) const {
auto it = sreg_value_map_.find(s_reg);
if (it != sreg_value_map_.end()) {
@@ -286,6 +290,7 @@
bool IsNonAliasingArray(uint16_t reg, uint16_t type) const;
void HandleNullCheck(MIR* mir, uint16_t reg);
void HandleRangeCheck(MIR* mir, uint16_t array, uint16_t index);
+ void HandleDivZeroCheck(MIR* mir, uint16_t reg);
void HandlePutObject(MIR* mir);
void HandleEscapingRef(uint16_t base);
void HandleInvokeArgs(const MIR* mir, const LocalValueNumbering* mir_lvn);
@@ -337,6 +342,7 @@
void MergeNonAliasingIFieldValues(const IFieldLocToValueMap::value_type& entry,
IFieldLocToValueMap::iterator hint);
void MergeNullChecked();
+ void MergeDivZeroChecked();
template <typename Map, Map LocalValueNumbering::*map_ptr, typename Versions>
void MergeAliasingValues(const typename Map::value_type& entry, typename Map::iterator hint);
@@ -371,6 +377,7 @@
// Range check and null check elimination.
RangeCheckSet range_checked_;
ValueNameSet null_checked_;
+ ValueNameSet div_zero_checked_;
// Reuse one vector for all merges to avoid leaking too much memory on the ArenaStack.
ScopedArenaVector<BasicBlockId> merge_names_;