Improve integer division on ARM in favor of power of 2 constant divisor

src/arm/lithium-codegen-arm.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1314 matching lines @@
         // This sequence could be replaced with 'mls' when
         // it gets implemented.
         __ mul(scratch, result, ip);
         __ sub(remainder, dividend, scratch);
       }
   }
 }
 
 
 void LCodeGen::DoDivI(LDivI* instr) {
+  if (instr->hydrogen()->HasPowerOf2Divisor()) {
+    Register dividend = ToRegister(instr->left());
+    int32_t divisor =
+        HConstant::cast(instr->hydrogen()->right())->Integer32Value();
+    int32_t test_value = 0;
+    int32_t power = 0;
+
+    if (divisor > 0) {
+      test_value = divisor - 1;
+      power = WhichPowerOf2(divisor);
+    } else {
+      // Check for (0 / -x) that will produce negative zero.
+      if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
+        __ tst(dividend, Operand(dividend));
+        DeoptimizeIf(eq, instr->environment());
+      }
+      // Check for (kMinInt / -1).
+      if (divisor == -1 && instr->hydrogen()->CheckFlag(HValue::kCanOverflow)) {
+        __ cmp(dividend, Operand(kMinInt));
+        DeoptimizeIf(eq, instr->environment());
+      }
+      test_value = - divisor - 1;
+      power = WhichPowerOf2(-divisor);
+    }
+
+    if (test_value != 0) {
+      // Deoptimize if remainder is not 0.
+      __ tst(dividend, Operand(test_value));
+      DeoptimizeIf(ne, instr->environment());
+      __ mov(dividend, Operand(dividend, ASR, power));
+    }
+    if (divisor < 0) __ rsb(dividend, dividend, Operand(0));
+
+    return;
+  }
+
   class DeferredDivI: public LDeferredCode {

[ulan, 2013/02/27 14:12:32]

Please move this class up to the beginning of the function.

    public:
     DeferredDivI(LCodeGen* codegen, LDivI* instr)
         : LDeferredCode(codegen), instr_(instr) { }
     virtual void Generate() {
       codegen()->DoDeferredBinaryOpStub(instr_->pointer_map(),
                                         instr_->left(),
                                         instr_->right(),
                                         Token::DIV);
     }
     virtual LInstruction* instr() { return instr_; }
@@ skipping 4755 matching lines @@
   __ sub(scratch, result, Operand(index, LSL, kPointerSizeLog2 - kSmiTagSize));
   __ ldr(result, FieldMemOperand(scratch,
                                  FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal