Quick: Eliminate check-cast guaranteed by instance-of.
Eliminate check-cast if the result of an instance-of with
the very same type on the same value is used to branch to
the check-cast's block or a dominator of it.
Note that there already exists a verifier-based elimination
of check-cast but it excludes check-cast on interfaces. This
new optimization works for interface types and, since it's
GVN-based, it can better recognize when the same reference
is used for instance-of and check-cast.
Change-Id: Ib315199805099d1cb0534bb4a90dc51baa409685
diff --git a/compiler/dex/local_value_numbering.cc b/compiler/dex/local_value_numbering.cc
index 99b6683..dc222b5 100644
--- a/compiler/dex/local_value_numbering.cc
+++ b/compiler/dex/local_value_numbering.cc
@@ -1520,7 +1520,6 @@
case Instruction::GOTO:
case Instruction::GOTO_16:
case Instruction::GOTO_32:
- case Instruction::CHECK_CAST:
case Instruction::THROW:
case Instruction::FILL_ARRAY_DATA:
case Instruction::PACKED_SWITCH:
@@ -1612,9 +1611,32 @@
HandleInvokeOrClInitOrAcquireOp(mir);
break;
+ case Instruction::INSTANCE_OF: {
+ uint16_t operand = GetOperandValue(mir->ssa_rep->uses[0]);
+ uint16_t type = mir->dalvikInsn.vC;
+ res = gvn_->LookupValue(Instruction::INSTANCE_OF, operand, type, kNoValue);
+ SetOperandValue(mir->ssa_rep->defs[0], res);
+ }
+ break;
+ case Instruction::CHECK_CAST:
+ if (gvn_->CanModify()) {
+ // Check if there was an instance-of operation on the same value and if we are
+ // in a block where its result is true. If so, we can eliminate the check-cast.
+ uint16_t operand = GetOperandValue(mir->ssa_rep->uses[0]);
+ uint16_t type = mir->dalvikInsn.vB;
+ uint16_t cond = gvn_->FindValue(Instruction::INSTANCE_OF, operand, type, kNoValue);
+ if (cond != kNoValue && gvn_->IsTrueInBlock(cond, Id())) {
+ if (gvn_->GetCompilationUnit()->verbose) {
+ LOG(INFO) << "Removing check-cast at 0x" << std::hex << mir->offset;
+ }
+ // Don't use kMirOpNop. Keep the check-cast as it defines the type of the register.
+ mir->optimization_flags |= MIR_IGNORE_CHECK_CAST;
+ }
+ }
+ break;
+
case Instruction::MOVE_RESULT:
case Instruction::MOVE_RESULT_OBJECT:
- case Instruction::INSTANCE_OF:
// 1 result, treat as unique each time, use result s_reg - will be unique.
res = GetOperandValue(mir->ssa_rep->defs[0]);
SetOperandValue(mir->ssa_rep->defs[0], res);