ARM: Fast path for compare against constant.

src/x64/lithium-codegen-x64.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 349 matching lines @@
 
 int LCodeGen::ToInteger32(LConstantOperand* op) const {
   Handle<Object> value = chunk_->LookupLiteral(op);
   ASSERT(chunk_->LookupLiteralRepresentation(op).IsInteger32());
   ASSERT(static_cast<double>(static_cast<int32_t>(value->Number())) ==
       value->Number());
   return static_cast<int32_t>(value->Number());
 }
 
 
+double LCodeGen::ToDouble(LConstantOperand* op) const {
+  Handle<Object> value = chunk_->LookupLiteral(op);
+  return value->Number();
+}
+
+
 Handle<Object> LCodeGen::ToHandle(LConstantOperand* op) const {
   Handle<Object> literal = chunk_->LookupLiteral(op);
   ASSERT(chunk_->LookupLiteralRepresentation(op).IsTagged());
   return literal;
 }
 
 
 Operand LCodeGen::ToOperand(LOperand* op) const {
   // Does not handle registers. In X64 assembler, plain registers are not
   // representable as an Operand.
@@ skipping 1132 matching lines @@
       break;
     case Token::IN:
     case Token::INSTANCEOF:
     default:
       UNREACHABLE();
   }
   return cond;
 }
 
 
-void LCodeGen::EmitCmpI(LOperand* left, LOperand* right) {
-  if (right->IsConstantOperand()) {
-    int32_t value = ToInteger32(LConstantOperand::cast(right));
-    if (left->IsRegister()) {
-      __ cmpl(ToRegister(left), Immediate(value));
-    } else {
-      __ cmpl(ToOperand(left), Immediate(value));
-    }
-  } else if (right->IsRegister()) {
-    __ cmpl(ToRegister(left), ToRegister(right));
-  } else {
-    __ cmpl(ToRegister(left), ToOperand(right));
-  }
-}
-
-
 void LCodeGen::DoCmpIDAndBranch(LCmpIDAndBranch* instr) {
   LOperand* left = instr->InputAt(0);
   LOperand* right = instr->InputAt(1);
   int false_block = chunk_->LookupDestination(instr->false_block_id());
   int true_block = chunk_->LookupDestination(instr->true_block_id());
+  Condition cc = TokenToCondition(instr->op(), instr->is_double());
 
-  if (instr->is_double()) {
-    // Don't base result on EFLAGS when a NaN is involved. Instead
-    // jump to the false block.
-    __ ucomisd(ToDoubleRegister(left), ToDoubleRegister(right));
-    __ j(parity_even, chunk_->GetAssemblyLabel(false_block));
+  if (left->IsConstantOperand() && right->IsConstantOperand()) {
+    // We can statically evaluate the comparison.
+    double left_val = ToDouble(LConstantOperand::cast(left));
+    double right_val = ToDouble(LConstantOperand::cast(right));
+    int next_block =
+      EvalComparison(instr->op(), left_val, right_val) ? true_block
+                                                       : false_block;
+    EmitGoto(next_block);
   } else {
-    EmitCmpI(left, right);
+    if (instr->is_double()) {
+      // Don't base result on EFLAGS when a NaN is involved. Instead
+      // jump to the false block.
+      __ ucomisd(ToDoubleRegister(left), ToDoubleRegister(right));
+      __ j(parity_even, chunk_->GetAssemblyLabel(false_block));
+    } else {
+      int32_t value;
+      if (right->IsConstantOperand()) {
+        value = ToInteger32(LConstantOperand::cast(right));
+        if (left->IsRegister()) {
+          __ cmpl(ToRegister(left), Immediate(value));
+        } else {
+          __ cmpl(ToOperand(left), Immediate(value));

[William Hesse, 2011/09/09 11:14:46]

This case is not needed, because left is created with "UseRegisterAtStart".
None of the new code is ever hit, because of how left and right are created in
lithium-x64.cc.
This needs to be changed - I would recommend
UseRegisterOrConstantAtStart for integer left
UseOrConstantAtStart for integer right

UseRegisterOrConstantAtStart for double left
UseRegisterOrConstantAtStart for double right.

Then the only one that could be a memory operand is right.

These changes should also be made to the ia32 platform.

[Alexandre, 2011/09/09 17:07:22]

I cleaned up this case. I hope ToRegister will work here.

Changed the integer register allocation in lithium.
For the double I added code to check that the two values are constant. Else we
use registers. Otherwise one double reg + one double constant fails.
I did the same on x64.

+        }
+      } else if (left->IsConstantOperand()) {
+        value = ToInteger32(LConstantOperand::cast(left));
+        if (right->IsRegister()) {
+          __ cmpl(ToRegister(right), Immediate(value));
+        } else {
+          __ cmpl(ToOperand(right), Immediate(value));
+        }
+        // We transposed the operands. Reverse the condition.
+        cc = ReverseCondition(cc);
+      } else {
+        __ cmp(ToRegister(left), ToOperand(right));

[William Hesse, 2011/09/09 11:14:46]

This must be a cmpl.

[Alexandre, 2011/09/09 17:07:22]

Done on x64.

+      }
+    }
+    EmitBranch(true_block, false_block, cc);
   }
-
-  Condition cc = TokenToCondition(instr->op(), instr->is_double());
-  EmitBranch(true_block, false_block, cc);
 }
 
 
 void LCodeGen::DoCmpObjectEqAndBranch(LCmpObjectEqAndBranch* instr) {
   Register left = ToRegister(instr->InputAt(0));
   Register right = ToRegister(instr->InputAt(1));
   int false_block = chunk_->LookupDestination(instr->false_block_id());
   int true_block = chunk_->LookupDestination(instr->true_block_id());
 
   __ cmpq(left, right);
@@ skipping 2598 matching lines @@
   RegisterEnvironmentForDeoptimization(environment);
   ASSERT(osr_pc_offset_ == -1);
   osr_pc_offset_ = masm()->pc_offset();
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64