Simple type tracking in the fast code generator.

src/fast-codegen.h

 // Copyright 2010 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 79 matching lines @@
   Register scratch0();
   Register scratch1();
   Register receiver_reg();
   Register context_reg();
 
   Register other_accumulator(Register reg) {
     ASSERT(reg.is(accumulator0()) || reg.is(accumulator1()));
     return (reg.is(accumulator0())) ? accumulator1() : accumulator0();
   }
 
+  // Flags are true if the respective register is statically known to hold a
+  // smi.  We do not track every register, only the accumulator registers.
+  bool is_smi(Register reg) { return (smi_bits_ & reg.bit()) != 0; }

[fschneider, 2010/02/10 15:14:33]

What happens if reg == no_reg? Maybe we should 
ASSERT(reg != noreg) here, since reg.bit() of no_reg is -1.

[Kevin Millikin (Chromium), 2010/02/11 08:30:09]

Done.

+  void set_as_smi(Register reg) { smi_bits_ = smi_bits_ | reg.bit(); }
+  void clear_as_smi(Register reg) { smi_bits_ = smi_bits_ & ~reg.bit(); }
+
   // AST node visit functions.
 #define DECLARE_VISIT(type) virtual void Visit##type(type* node);
   AST_NODE_LIST(DECLARE_VISIT)
 #undef DECLARE_VISIT
 
   // Emit code to load the receiver from the stack into receiver_reg.
   void EmitLoadReceiver();
 
   // Emit code to load a global variable directly from a global property
   // cell into the destination register.
@@ skipping 12 matching lines @@
 
   // Emit a bitwise or operation.  The left operand is in accumulator1 and
   // the right is in accumulator0.  The result should be left in the
   // destination register.
   void EmitBitOr();
 
   MacroAssembler* masm_;
   CompilationInfo* info_;
   Label bailout_;
   Register destination_;
+  uint32_t smi_bits_;

[fschneider, 2010/02/10 15:14:33]

smi_bits_ should be initialized to 0?

[Kevin Millikin (Chromium), 2010/02/11 08:30:09]

Done.

 
   DISALLOW_COPY_AND_ASSIGN(FastCodeGenerator);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_FAST_CODEGEN_H_