Support check-cast elision in DEX-to-DEX compiler.
Bug: 9648428
Replaces safe check-cast by 2 consecutive nop instructions.
Change-Id: I2cd99c629a6a00a6e0effc853c3439bc92683d6d
diff --git a/compiler/dex/dex_to_dex_compiler.cc b/compiler/dex/dex_to_dex_compiler.cc
index ee68a5d..4419fed 100644
--- a/compiler/dex/dex_to_dex_compiler.cc
+++ b/compiler/dex/dex_to_dex_compiler.cc
@@ -30,8 +30,8 @@
// Controls quickening activation.
const bool kEnableQuickening = true;
-// Controls logging.
-const bool kEnableLogging = false;
+// Control check-cast elision.
+const bool kEnableCheckCastEllision = true;
class DexCompiler {
public:
@@ -59,6 +59,11 @@
// a barrier is required.
void CompileReturnVoid(Instruction* inst, uint32_t dex_pc);
+ // Compiles a CHECK-CAST into 2 NOP instructions if it is known to be safe. In
+ // this case, returns the second NOP instruction pointer. Otherwise, returns
+ // the given "inst".
+ Instruction* CompileCheckCast(Instruction* inst, uint32_t dex_pc);
+
// Compiles a field access into a quick field access.
// The field index is replaced by an offset within an Object where we can read
// from / write to this field. Therefore, this does not involve any resolution
@@ -145,6 +150,10 @@
CompileReturnVoid(inst, dex_pc);
break;
+ case Instruction::CHECK_CAST:
+ inst = CompileCheckCast(inst, dex_pc);
+ break;
+
case Instruction::IGET:
CompileInstanceFieldAccess(inst, dex_pc, Instruction::IGET_QUICK, false);
break;
@@ -202,16 +211,44 @@
return;
}
// Replace RETURN_VOID by RETURN_VOID_BARRIER.
- if (kEnableLogging) {
- LOG(INFO) << "Replacing " << Instruction::Name(inst->Opcode())
- << " by " << Instruction::Name(Instruction::RETURN_VOID_BARRIER)
- << " at dex pc " << StringPrintf("0x%x", dex_pc) << " in method "
- << PrettyMethod(unit_.GetDexMethodIndex(), GetDexFile(), true);
- }
+ VLOG(compiler) << "Replacing " << Instruction::Name(inst->Opcode())
+ << " by " << Instruction::Name(Instruction::RETURN_VOID_BARRIER)
+ << " at dex pc " << StringPrintf("0x%x", dex_pc) << " in method "
+ << PrettyMethod(unit_.GetDexMethodIndex(), GetDexFile(), true);
ScopedDexWriteAccess sdwa(GetModifiableDexFile(), inst, 2u);
inst->SetOpcode(Instruction::RETURN_VOID_BARRIER);
}
+Instruction* DexCompiler::CompileCheckCast(Instruction* inst, uint32_t dex_pc) {
+ if (!kEnableCheckCastEllision) {
+ return inst;
+ }
+ MethodReference referrer(&GetDexFile(), unit_.GetDexMethodIndex());
+ if (!driver_.IsSafeCast(referrer, dex_pc)) {
+ return inst;
+ }
+ // Ok, this is a safe cast. Since the "check-cast" instruction size is 2 code
+ // units and a "nop" instruction size is 1 code unit, we need to replace it by
+ // 2 consecutive NOP instructions.
+ // Because the caller loops over instructions by calling Instruction::Next onto
+ // the current instruction, we need to return the 2nd NOP instruction. Indeed,
+ // its next instruction is the former check-cast's next instruction.
+ VLOG(compiler) << "Removing " << Instruction::Name(inst->Opcode())
+ << " by replacing it with 2 NOPs at dex pc "
+ << StringPrintf("0x%x", dex_pc) << " in method "
+ << PrettyMethod(unit_.GetDexMethodIndex(), GetDexFile(), true);
+ // We are modifying 4 consecutive bytes.
+ ScopedDexWriteAccess sdwa(GetModifiableDexFile(), inst, 4u);
+ inst->SetOpcode(Instruction::NOP);
+ inst->SetVRegA_10x(0u); // keep compliant with verifier.
+ // Get to next instruction which is the second half of check-cast and replace
+ // it by a NOP.
+ inst = const_cast<Instruction*>(inst->Next());
+ inst->SetOpcode(Instruction::NOP);
+ inst->SetVRegA_10x(0u); // keep compliant with verifier.
+ return inst;
+}
+
void DexCompiler::CompileInstanceFieldAccess(Instruction* inst,
uint32_t dex_pc,
Instruction::Code new_opcode,
@@ -225,15 +262,12 @@
bool fast_path = driver_.ComputeInstanceFieldInfo(field_idx, &unit_, field_offset,
is_volatile, is_put);
if (fast_path && !is_volatile && IsUint(16, field_offset)) {
- // TODO: use VLOG ?
- if (kEnableLogging) {
- LOG(INFO) << "Quickening " << Instruction::Name(inst->Opcode())
- << " to " << Instruction::Name(new_opcode)
- << " by replacing field index " << field_idx
- << " by field offset " << field_offset
- << " at dex pc " << StringPrintf("0x%x", dex_pc) << " in method "
- << PrettyMethod(unit_.GetDexMethodIndex(), GetDexFile(), true);
- }
+ VLOG(compiler) << "Quickening " << Instruction::Name(inst->Opcode())
+ << " to " << Instruction::Name(new_opcode)
+ << " by replacing field index " << field_idx
+ << " by field offset " << field_offset
+ << " at dex pc " << StringPrintf("0x%x", dex_pc) << " in method "
+ << PrettyMethod(unit_.GetDexMethodIndex(), GetDexFile(), true);
// We are modifying 4 consecutive bytes.
ScopedDexWriteAccess sdwa(GetModifiableDexFile(), inst, 4u);
inst->SetOpcode(new_opcode);
@@ -263,16 +297,13 @@
// TODO: support devirtualization.
if (fast_path && original_invoke_type == invoke_type) {
if (vtable_idx >= 0 && IsUint(16, vtable_idx)) {
- // TODO: use VLOG ?
- if (kEnableLogging) {
- LOG(INFO) << "Quickening " << Instruction::Name(inst->Opcode())
- << "(" << PrettyMethod(method_idx, GetDexFile(), true) << ")"
- << " to " << Instruction::Name(new_opcode)
- << " by replacing method index " << method_idx
- << " by vtable index " << vtable_idx
- << " at dex pc " << StringPrintf("0x%x", dex_pc) << " in method "
- << PrettyMethod(unit_.GetDexMethodIndex(), GetDexFile(), true);
- }
+ VLOG(compiler) << "Quickening " << Instruction::Name(inst->Opcode())
+ << "(" << PrettyMethod(method_idx, GetDexFile(), true) << ")"
+ << " to " << Instruction::Name(new_opcode)
+ << " by replacing method index " << method_idx
+ << " by vtable index " << vtable_idx
+ << " at dex pc " << StringPrintf("0x%x", dex_pc) << " in method "
+ << PrettyMethod(unit_.GetDexMethodIndex(), GetDexFile(), true);
// We are modifying 4 consecutive bytes.
ScopedDexWriteAccess sdwa(GetModifiableDexFile(), inst, 4u);
inst->SetOpcode(new_opcode);
diff --git a/runtime/dex_instruction.h b/runtime/dex_instruction.h
index 7d078f9..ff81659 100644
--- a/runtime/dex_instruction.h
+++ b/runtime/dex_instruction.h
@@ -292,6 +292,12 @@
insns[0] = (insns[0] & 0xff00) | static_cast<uint16_t>(opcode);
}
+ void SetVRegA_10x(uint8_t val) {
+ DCHECK(FormatOf(Opcode()) == k10x);
+ uint16_t* insns = reinterpret_cast<uint16_t*>(this);
+ insns[0] = (val << 8) | (insns[0] & 0x00ff);
+ }
+
void SetVRegB_3rc(uint16_t val) {
DCHECK(FormatOf(Opcode()) == k3rc);
uint16_t* insns = reinterpret_cast<uint16_t*>(this);
