Fix conditional jump over jmp (X86/X86-64/ARM32)
Optimize the code generation for 'if' statements to jump to the
'false' block if the next block to be generated is the 'true' block.
Add an X86-64 test for this case.
Note that ARM64 & MIPS64 have not been updated.
Change-Id: Iebb1352feb9d3bd0142d8b0621a2e3069a708ea7
Signed-off-by: Mark Mendell <mark.p.mendell@intel.com>
diff --git a/compiler/optimizing/code_generator_x86_64.cc b/compiler/optimizing/code_generator_x86_64.cc
index 5218d70..b5abec2 100644
--- a/compiler/optimizing/code_generator_x86_64.cc
+++ b/compiler/optimizing/code_generator_x86_64.cc
@@ -1183,16 +1183,20 @@
DCHECK_EQ(cond_value, 0);
}
} else {
- bool is_materialized =
- !cond->IsCondition() || cond->AsCondition()->NeedsMaterialization();
+ HCondition* condition = cond->AsCondition();
+ bool is_materialized = condition == nullptr || condition->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. We can't use the eflags on FP conditions if they are
// materialized due to the complex branching.
- Primitive::Type type = cond->IsCondition() ? cond->InputAt(0)->GetType() : Primitive::kPrimInt;
- bool eflags_set = cond->IsCondition()
- && cond->AsCondition()->IsBeforeWhenDisregardMoves(instruction)
+ Primitive::Type type = (condition != nullptr)
+ ? cond->InputAt(0)->GetType()
+ : Primitive::kPrimInt;
+ bool eflags_set = condition != nullptr
+ && condition->IsBeforeWhenDisregardMoves(instruction)
&& !Primitive::IsFloatingPointType(type);
+ // Can we optimize the jump if we know that the next block is the true case?
+ bool can_jump_to_false = CanReverseCondition(always_true_target, false_target, condition);
if (is_materialized) {
if (!eflags_set) {
@@ -1204,9 +1208,17 @@
__ cmpl(Address(CpuRegister(RSP), lhs.GetStackIndex()),
Immediate(0));
}
+ if (can_jump_to_false) {
+ __ j(kEqual, false_target);
+ return;
+ }
__ j(kNotEqual, true_target);
} else {
- __ j(X86_64IntegerCondition(cond->AsCondition()->GetCondition()), true_target);
+ if (can_jump_to_false) {
+ __ j(X86_64IntegerCondition(condition->GetOppositeCondition()), false_target);
+ return;
+ }
+ __ j(X86_64IntegerCondition(condition->GetCondition()), true_target);
}
} else {
// Condition has not been materialized, use its inputs as the
@@ -1215,7 +1227,7 @@
// Is this a long or FP comparison that has been folded into the HCondition?
if (type == Primitive::kPrimLong || Primitive::IsFloatingPointType(type)) {
// Generate the comparison directly.
- GenerateCompareTestAndBranch(instruction->AsIf(), cond->AsCondition(),
+ GenerateCompareTestAndBranch(instruction->AsIf(), condition,
true_target, false_target, always_true_target);
return;
}
@@ -1235,7 +1247,13 @@
__ cmpl(lhs.AsRegister<CpuRegister>(),
Address(CpuRegister(RSP), rhs.GetStackIndex()));
}
- __ j(X86_64IntegerCondition(cond->AsCondition()->GetCondition()), true_target);
+
+ if (can_jump_to_false) {
+ __ j(X86_64IntegerCondition(condition->GetOppositeCondition()), false_target);
+ return;
+ }
+
+ __ j(X86_64IntegerCondition(condition->GetCondition()), true_target);
}
}
if (false_target != nullptr) {