Improve modulo operation in lithium on IA32.

src/ia32/lithium-codegen-ia32.cc

 // Copyright 2011 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 777 matching lines @@
     __ neg(dividend);
     if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
       __ j(not_zero, &done);
       DeoptimizeIf(no_condition, instr->environment());
     }
     __ bind(&positive_dividend);
     __ and_(dividend, divisor - 1);
     __ bind(&done);
   } else {
     LOperand* right = instr->InputAt(1);
+    NearLabel done, remainder_eq_dividend, slow, do_subtraction, both_positive;

[Søren Thygesen Gjesse, 2011/04/27 14:11:43]

Please set up Register variables for left as well:

Register left = ToRegister(instr->InputAt(0));

And use it below instead of eax it more readable.

     ASSERT(ToRegister(instr->InputAt(0)).is(eax));
     ASSERT(ToRegister(instr->result()).is(edx));
 
     Register right_reg = ToRegister(right);
     ASSERT(!right_reg.is(eax));
     ASSERT(!right_reg.is(edx));
 
     // Check for x % 0.
     if (instr->hydrogen()->CheckFlag(HValue::kCanBeDivByZero)) {
       __ test(right_reg, ToOperand(right));
       DeoptimizeIf(zero, instr->environment());
     }
 
+    __ test(eax, Operand(eax));
+    __ j(zero, &remainder_eq_dividend);
+    __ j(sign, &slow);
+
+    __ test(right_reg, Operand(right_reg));
+    __ j(not_sign, &both_positive);
+    // The sign of the divisor doesn't matter.
+    __ neg(right_reg);
+
+    __ bind(&both_positive);
+    // If the dividend is smaller than the nonnegative
+    // divisor, the dividend is the result.
+    __ cmp(eax, Operand(right_reg));
+    __ j(less, &remainder_eq_dividend);
+
+    // Check if the divisor is a PowerOfTwo integer.
+    Register scratch = ToRegister(instr->TempAt(0));
+    __ mov(scratch, right_reg);
+    __ sub(Operand(scratch), Immediate(1));
+    __ test(scratch, Operand(right_reg));
+    __ j(not_zero, &do_subtraction);
+    __ and_(eax, Operand(scratch));
+    __ jmp(&remainder_eq_dividend);
+
+    __ bind(&do_subtraction);
+    const int kUnfolds = 3;
+    // Try a few subtractions of the dividend.
+    __ mov(scratch, eax);
+    for (int i = 0; i < kUnfolds; i++) {
+      // Reduce the dividend by the divisor.
+      __ sub(eax, Operand(right_reg));
+      // Check if the dividend is less than the divisor.
+      __ cmp(eax, Operand(right_reg));
+      __ j(less, &remainder_eq_dividend);
+    }
+    __ mov(eax, scratch);
+
+    // Slow case, using idiv instruction.
+    __ bind(&slow);
     // Sign extend to edx.
     __ cdq();
 
     // Check for (0 % -x) that will produce negative zero.
     if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
       NearLabel positive_left;
       NearLabel done;
       __ test(eax, Operand(eax));
       __ j(not_sign, &positive_left);
       __ idiv(right_reg);
 
       // Test the remainder for 0, because then the result would be -0.
       __ test(edx, Operand(edx));
       __ j(not_zero, &done);
 
       DeoptimizeIf(no_condition, instr->environment());
       __ bind(&positive_left);
       __ idiv(right_reg);
       __ bind(&done);
     } else {
       __ idiv(right_reg);
     }
+    __ jmp(&done);
+
+    __ bind(&remainder_eq_dividend);
+    __ mov(edx, eax);
+
+    __ bind(&done);
   }
 }
 
 
 void LCodeGen::DoDivI(LDivI* instr) {
   LOperand* right = instr->InputAt(1);
   ASSERT(ToRegister(instr->result()).is(eax));
   ASSERT(ToRegister(instr->InputAt(0)).is(eax));
   ASSERT(!ToRegister(instr->InputAt(1)).is(eax));
   ASSERT(!ToRegister(instr->InputAt(1)).is(edx));
@@ skipping 3320 matching lines @@
   ASSERT(osr_pc_offset_ == -1);
   osr_pc_offset_ = masm()->pc_offset();
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32