Turn constant conditional jumps into unconditional jumps.
If a condition (input of an art::HIf instruction) is
constant (an art::HConstant object), evaluate it at
compile time and generate an unconditional branch
instruction if it is true (in lieu of a conditional jump).
Change-Id: I262e43ffe66d5c25dbbfa98092a41c8b3c4c75d6
diff --git a/compiler/optimizing/code_generator_x86.cc b/compiler/optimizing/code_generator_x86.cc
index 34fa46e..5fc3895 100644
--- a/compiler/optimizing/code_generator_x86.cc
+++ b/compiler/optimizing/code_generator_x86.cc
@@ -577,42 +577,60 @@
void InstructionCodeGeneratorX86::VisitIf(HIf* if_instr) {
HInstruction* cond = if_instr->InputAt(0);
- bool materialized = !cond->IsCondition() || cond->AsCondition()->NeedsMaterialization();
- // Moves do not affect the eflags register, so if the condition is evaluated
- // just before the if, we don't need to evaluate it again.
- bool eflags_set = cond->IsCondition()
- && cond->AsCondition()->IsBeforeWhenDisregardMoves(if_instr);
- if (materialized) {
- if (!eflags_set) {
- // Materialized condition, compare against 0.
- Location lhs = if_instr->GetLocations()->InAt(0);
- if (lhs.IsRegister()) {
- __ cmpl(lhs.As<Register>(), Immediate(0));
- } else {
- __ cmpl(Address(ESP, lhs.GetStackIndex()), Immediate(0));
+ if (cond->IsIntConstant()) {
+ // Constant condition, statically compared against 1.
+ int32_t cond_value = cond->AsIntConstant()->GetValue();
+ if (cond_value == 1) {
+ if (!codegen_->GoesToNextBlock(if_instr->GetBlock(),
+ if_instr->IfTrueSuccessor())) {
+ __ jmp(codegen_->GetLabelOf(if_instr->IfTrueSuccessor()));
}
- __ j(kNotEqual, codegen_->GetLabelOf(if_instr->IfTrueSuccessor()));
+ return;
} else {
+ DCHECK_EQ(cond_value, 0);
+ }
+ } else {
+ bool materialized =
+ !cond->IsCondition() || cond->AsCondition()->NeedsMaterialization();
+ // Moves do not affect the eflags register, so if the condition is
+ // evaluated just before the if, we don't need to evaluate it
+ // again.
+ bool eflags_set = cond->IsCondition()
+ && cond->AsCondition()->IsBeforeWhenDisregardMoves(if_instr);
+ if (materialized) {
+ if (!eflags_set) {
+ // Materialized condition, compare against 0.
+ Location lhs = if_instr->GetLocations()->InAt(0);
+ if (lhs.IsRegister()) {
+ __ cmpl(lhs.As<Register>(), Immediate(0));
+ } else {
+ __ cmpl(Address(ESP, lhs.GetStackIndex()), Immediate(0));
+ }
+ __ j(kNotEqual, codegen_->GetLabelOf(if_instr->IfTrueSuccessor()));
+ } else {
+ __ j(X86Condition(cond->AsCondition()->GetCondition()),
+ codegen_->GetLabelOf(if_instr->IfTrueSuccessor()));
+ }
+ } else {
+ Location lhs = cond->GetLocations()->InAt(0);
+ Location rhs = cond->GetLocations()->InAt(1);
+ // LHS is guaranteed to be in a register (see
+ // LocationsBuilderX86::VisitCondition).
+ if (rhs.IsRegister()) {
+ __ cmpl(lhs.As<Register>(), rhs.As<Register>());
+ } else if (rhs.IsConstant()) {
+ HIntConstant* instruction = rhs.GetConstant()->AsIntConstant();
+ Immediate imm(instruction->AsIntConstant()->GetValue());
+ __ cmpl(lhs.As<Register>(), imm);
+ } else {
+ __ cmpl(lhs.As<Register>(), Address(ESP, rhs.GetStackIndex()));
+ }
__ j(X86Condition(cond->AsCondition()->GetCondition()),
codegen_->GetLabelOf(if_instr->IfTrueSuccessor()));
}
- } else {
- Location lhs = cond->GetLocations()->InAt(0);
- Location rhs = cond->GetLocations()->InAt(1);
- // LHS is guaranteed to be in a register (see LocationsBuilderX86::VisitCondition).
- if (rhs.IsRegister()) {
- __ cmpl(lhs.As<Register>(), rhs.As<Register>());
- } else if (rhs.IsConstant()) {
- HIntConstant* instruction = rhs.GetConstant()->AsIntConstant();
- Immediate imm(instruction->AsIntConstant()->GetValue());
- __ cmpl(lhs.As<Register>(), imm);
- } else {
- __ cmpl(lhs.As<Register>(), Address(ESP, rhs.GetStackIndex()));
- }
- __ j(X86Condition(cond->AsCondition()->GetCondition()),
- codegen_->GetLabelOf(if_instr->IfTrueSuccessor()));
}
- if (!codegen_->GoesToNextBlock(if_instr->GetBlock(), if_instr->IfFalseSuccessor())) {
+ if (!codegen_->GoesToNextBlock(if_instr->GetBlock(),
+ if_instr->IfFalseSuccessor())) {
__ jmp(codegen_->GetLabelOf(if_instr->IfFalseSuccessor()));
}
}
@@ -747,6 +765,7 @@
}
void InstructionCodeGeneratorX86::VisitIntConstant(HIntConstant* constant) {
+ // Will be generated at use site.
}
void LocationsBuilderX86::VisitLongConstant(HLongConstant* constant) {