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

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

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/code-generator.h"
 #include "src/compilation-info.h"
 #include "src/compiler/code-generator-impl.h"
 #include "src/compiler/gap-resolver.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/osr.h"
@@ skipping 1698 matching lines @@
   Label false_value;
   DCHECK_NE(0u, instr->OutputCount());
   Register result = i.OutputRegister(instr->OutputCount() - 1);
   Condition cc = kNoCondition;
   // MIPS does not have condition code flags, so compare and branch are
   // implemented differently than on the other arch's. The compare operations
   // emit mips psuedo-instructions, which are checked and handled here.
 
   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);
     }
     return;
   } else if (instr->arch_opcode() == kMipsAddOvf ||
              instr->arch_opcode() == kMipsSubOvf ||
              instr->arch_opcode() == kMipsMulOvf) {
     Label flabel, tlabel;
     switch (instr->arch_opcode()) {
@@ skipping 537 matching lines @@
       padding_size -= v8::internal::Assembler::kInstrSize;
     }
   }
 }
 
 #undef __
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8