MIPS: Reduce Baker read barrier code size overhead

Test: booted MIPS64 (with 2nd arch MIPS32R6) in QEMU
Test: test-art-target-gtest
Test: testrunner.py --target --optimizing
Test: same tests as above on CI20
Test: booted MIPS32 and MIPS64 in QEMU with poisoning
      in configurations:
      - with Baker read barrier thunks
      - without Baker read barrier thunks
      - ART_READ_BARRIER_TYPE=TABLELOOKUP

Change-Id: I79f320bf8862a04215c76cfeff3118ebc87f7ef2
diff --git a/compiler/utils/mips64/assembler_mips64.cc b/compiler/utils/mips64/assembler_mips64.cc
index 24900a7..9039854 100644
--- a/compiler/utils/mips64/assembler_mips64.cc
+++ b/compiler/utils/mips64/assembler_mips64.cc
@@ -795,6 +795,10 @@
   EmitFI(0x11, 0xD, ft, imm16);
 }
 
+void Mips64Assembler::Beqz(GpuRegister rt, uint16_t imm16) {
+  EmitI(0x4, ZERO, rt, imm16);
+}
+
 void Mips64Assembler::EmitBcondc(BranchCondition cond,
                                  GpuRegister rs,
                                  GpuRegister rt,
diff --git a/compiler/utils/mips64/assembler_mips64.h b/compiler/utils/mips64/assembler_mips64.h
index 773db9b..5e88033 100644
--- a/compiler/utils/mips64/assembler_mips64.h
+++ b/compiler/utils/mips64/assembler_mips64.h
@@ -563,6 +563,7 @@
   void Bnezc(GpuRegister rs, uint32_t imm21);
   void Bc1eqz(FpuRegister ft, uint16_t imm16);
   void Bc1nez(FpuRegister ft, uint16_t imm16);
+  void Beqz(GpuRegister rt, uint16_t imm16);
 
   void AddS(FpuRegister fd, FpuRegister fs, FpuRegister ft);
   void SubS(FpuRegister fd, FpuRegister fs, FpuRegister ft);