ART: Reduce the instructions generated by packed switch.
Implement Vladimir Marko's suggestion. The new compare/jump series
reduce the number of instructions from (2*n+1) to (1.5*n+3).
Generate normal compare/jump series when numEntries <= 3.
Generate optimal compare/jump series when numEntries <= threshold.
Generate jump tables otherwise.
Change-Id: I425547b6787057c7fa84e71f17c145b63b208633
diff --git a/compiler/optimizing/code_generator_x86.h b/compiler/optimizing/code_generator_x86.h
index 064051c..f9403a6 100644
--- a/compiler/optimizing/code_generator_x86.h
+++ b/compiler/optimizing/code_generator_x86.h
@@ -195,6 +195,11 @@
X86Assembler* GetAssembler() const { return assembler_; }
+ // The compare/jump sequence will generate about (1.5 * num_entries) instructions. A jump
+ // table version generates 7 instructions and num_entries literals. Compare/jump sequence will
+ // generates less code/data with a small num_entries.
+ static constexpr uint32_t kPackedSwitchJumpTableThreshold = 5;
+
private:
// Generate code for the given suspend check. If not null, `successor`
// is the block to branch to if the suspend check is not needed, and after
@@ -236,6 +241,11 @@
void GenerateFPJumps(HCondition* cond, Label* true_label, Label* false_label);
void GenerateLongComparesAndJumps(HCondition* cond, Label* true_label, Label* false_label);
void HandleGoto(HInstruction* got, HBasicBlock* successor);
+ void GenPackedSwitchWithCompares(Register value_reg,
+ int32_t lower_bound,
+ uint32_t num_entries,
+ HBasicBlock* switch_block,
+ HBasicBlock* default_block);
X86Assembler* const assembler_;
CodeGeneratorX86* const codegen_;