Revert "Revert "ART: Reduce the instructions generated by packed switch.""
This reverts commit b4c137630fd2226ad07dfd178ab15725374220f1.
The underlying issue was fixed by https://android-review.googlesource.com/188271 .
Bug: 26121945
Change-Id: I58b08eb1a9f0a5c861f8cda93522af64bcf63920
diff --git a/compiler/optimizing/code_generator_arm.cc b/compiler/optimizing/code_generator_arm.cc
index ac6b5e8..0a26786 100644
--- a/compiler/optimizing/code_generator_arm.cc
+++ b/compiler/optimizing/code_generator_arm.cc
@@ -59,7 +59,7 @@
// S registers. Therefore there is no need to block it.
static constexpr DRegister DTMP = D31;
-static constexpr uint32_t kPackedSwitchJumpTableThreshold = 6;
+static constexpr uint32_t kPackedSwitchCompareJumpThreshold = 7;
#define __ down_cast<ArmAssembler*>(codegen->GetAssembler())->
#define QUICK_ENTRY_POINT(x) QUICK_ENTRYPOINT_OFFSET(kArmWordSize, x).Int32Value()
@@ -6106,7 +6106,7 @@
LocationSummary* locations =
new (GetGraph()->GetArena()) LocationSummary(switch_instr, LocationSummary::kNoCall);
locations->SetInAt(0, Location::RequiresRegister());
- if (switch_instr->GetNumEntries() >= kPackedSwitchJumpTableThreshold &&
+ if (switch_instr->GetNumEntries() > kPackedSwitchCompareJumpThreshold &&
codegen_->GetAssembler()->IsThumb()) {
locations->AddTemp(Location::RequiresRegister()); // We need a temp for the table base.
if (switch_instr->GetStartValue() != 0) {
@@ -6122,12 +6122,30 @@
Register value_reg = locations->InAt(0).AsRegister<Register>();
HBasicBlock* default_block = switch_instr->GetDefaultBlock();
- if (num_entries < kPackedSwitchJumpTableThreshold || !codegen_->GetAssembler()->IsThumb()) {
+ if (num_entries <= kPackedSwitchCompareJumpThreshold || !codegen_->GetAssembler()->IsThumb()) {
// Create a series of compare/jumps.
+ Register temp_reg = IP;
+ // Note: It is fine for the below AddConstantSetFlags() using IP register to temporarily store
+ // the immediate, because IP is used as the destination register. For the other
+ // AddConstantSetFlags() and GenerateCompareWithImmediate(), the immediate values are constant,
+ // and they can be encoded in the instruction without making use of IP register.
+ __ AddConstantSetFlags(temp_reg, value_reg, -lower_bound);
+
const ArenaVector<HBasicBlock*>& successors = switch_instr->GetBlock()->GetSuccessors();
- for (uint32_t i = 0; i < num_entries; i++) {
- GenerateCompareWithImmediate(value_reg, lower_bound + i);
- __ b(codegen_->GetLabelOf(successors[i]), EQ);
+ // Jump to successors[0] if value == lower_bound.
+ __ b(codegen_->GetLabelOf(successors[0]), EQ);
+ int32_t last_index = 0;
+ for (; num_entries - last_index > 2; last_index += 2) {
+ __ AddConstantSetFlags(temp_reg, temp_reg, -2);
+ // Jump to successors[last_index + 1] if value < case_value[last_index + 2].
+ __ b(codegen_->GetLabelOf(successors[last_index + 1]), LO);
+ // Jump to successors[last_index + 2] if value == case_value[last_index + 2].
+ __ b(codegen_->GetLabelOf(successors[last_index + 2]), EQ);
+ }
+ if (num_entries - last_index == 2) {
+ // The last missing case_value.
+ GenerateCompareWithImmediate(temp_reg, 1);
+ __ b(codegen_->GetLabelOf(successors[last_index + 1]), EQ);
}
// And the default for any other value.