LibJS/JIT: Use the x86_64 setcc instruction to remove a branch

lanmonster · Nov 14, 2023 · d3b3e49 · d3b3e49
1 parent 1d76738
commit d3b3e49
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Showing 3 changed files with 17 additions and 16 deletions.
diff --git a/Userland/Libraries/LibJIT/X86_64/Assembler.h b/Userland/Libraries/LibJIT/X86_64/Assembler.h
@@ -569,6 +569,14 @@ struct X86_64Assembler {
  jump_if(condition, label);
  }
 
+ void set_if(Condition condition, Operand dst)
+ {
+ emit_rex_for_slash(dst, REX_W::No);
+ emit8(0x0f);
+ emit8(0x90 | to_underlying(condition));
+ emit_modrm_slash(0, dst);
+ }
+
  void sign_extend_32_to_64_bits(Reg reg)
  {
  mov32(Operand::Register(reg), Operand::Register(reg), Extension::SignExtend);

diff --git a/Userland/Libraries/LibJS/JIT/Compiler.cpp b/Userland/Libraries/LibJS/JIT/Compiler.cpp
@@ -1098,27 +1098,19 @@ void Compiler::compile_mul(Bytecode::Op::Mul const& op)
  Assembler::Label end {}; \
  \
  branch_if_both_int32(ARG1, ARG2, [&] { \
- Assembler::Label true_case {}; \
- \
  m_assembler.sign_extend_32_to_64_bits(ARG1); \
  m_assembler.sign_extend_32_to_64_bits(ARG2); \
  \
- m_assembler.jump_if( \
- Assembler::Operand::Register(ARG1), \
- Assembler::Condition::AssemblerCondition, \
- Assembler::Operand::Register(ARG2), \
- true_case); \
- \
+ /* accumulator = SHIFTED_BOOLEAN_TAG | (arg1 condition arg2) */ \
  m_assembler.mov( \
  Assembler::Operand::Register(GPR0), \
- Assembler::Operand::Imm(Value(false).encoded())); \
- store_accumulator(GPR0); \
- m_assembler.jump(end); \
- \
- true_case.link(m_assembler); \
- m_assembler.mov( \
- Assembler::Operand::Register(GPR0), \
- Assembler::Operand::Imm(Value(true).encoded())); \
+ Assembler::Operand::Imm(SHIFTED_BOOLEAN_TAG)); \
+ m_assembler.cmp( \
+ Assembler::Operand::Register(ARG1), \
+ Assembler::Operand::Register(ARG2)); \
+ m_assembler.set_if( \
+ Assembler::Condition::AssemblerCondition, \
+ Assembler::Operand::Register(GPR0)); /* sets only first byte */ \
  store_accumulator(GPR0); \
  \
  m_assembler.jump(end); \

diff --git a/Userland/Libraries/LibJS/Runtime/Value.h b/Userland/Libraries/LibJS/Runtime/Value.h
@@ -104,6 +104,7 @@ static_assert((EMPTY_TAG & IS_NULLISH_EXTRACT_PATTERN) != IS_NULLISH_PATTERN);
 
 static constexpr u64 TAG_EXTRACTION = 0xFFFF000000000000;
 static constexpr u64 TAG_SHIFT = 48;
+static constexpr u64 SHIFTED_BOOLEAN_TAG = BOOLEAN_TAG << TAG_SHIFT;
 static constexpr u64 SHIFTED_INT32_TAG = INT32_TAG << TAG_SHIFT;
 static constexpr u64 SHIFTED_IS_CELL_PATTERN = IS_CELL_PATTERN << TAG_SHIFT;