MIPS[64]: Optimize kMips[64]Tst in code-generator-mips[64].cc

src/compiler/mips/code-generator-mips.cc

Index: src/compiler/mips/code-generator-mips.cc
diff --git a/src/compiler/mips/code-generator-mips.cc b/src/compiler/mips/code-generator-mips.cc
index ee374798b1e309df37be2e6ee4ae767ed6e69a4d..17b27972861145451ebdd8b7c90ff3863f3d0b48 100644
--- a/src/compiler/mips/code-generator-mips.cc
+++ b/src/compiler/mips/code-generator-mips.cc
@@ -1716,8 +1716,13 @@ void CodeGenerator::AssembleArchBoolean(Instruction* instr,
 
   if (instr->arch_opcode() == kMipsTst) {
     cc = FlagsConditionToConditionTst(condition);
-    __ And(kScratchReg, i.InputRegister(0), i.InputOperand(1));
-    __ Sltu(result, zero_reg, kScratchReg);
+    if (instr->InputAt(1)->IsImmediate() &&

[dusan.simicic, 2016/11/09 12:40:49]

I think this can be generalised for all 2^n constants, where n=0..31, not only
for n=0 (imm value 1). Not sure how often we are checking for all of this
constant values (2,4,8,16,...), but maybe this could bring some benefit.

+        i.InputOperand(1).immediate() == 1) {
+      __ Ext(result, i.InputRegister(0), 0, 1);
+    } else {
+      __ And(kScratchReg, i.InputRegister(0), i.InputOperand(1));
+      __ Sltu(result, zero_reg, kScratchReg);
+    }
     if (cc == eq) {
       // Sltu produces 0 for equality, invert the result.
       __ xori(result, result, 1);