MIPS: Optimize AccessArgumentsAt.

src/mips/lithium-codegen-mips.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 3019 matching lines @@
   Register to_reg = ToRegister(instr->result());
   Register from_reg  = ToRegister(instr->object());
   __ lw(to_reg, FieldMemOperand(from_reg,
                                 ExternalArray::kExternalPointerOffset));
 }
 
 
 void LCodeGen::DoAccessArgumentsAt(LAccessArgumentsAt* instr) {
   Register arguments = ToRegister(instr->arguments());
   Register result = ToRegister(instr->result());
-  if (instr->length()->IsConstantOperand() &&
-      instr->index()->IsConstantOperand()) {
+  // There are two words between the frame pointer and the last argument.
+  // Subtracting from length accounts for one of them add one more.
+  if (instr->length()->IsConstantOperand()) {
+    int const_length = ToInteger32(LConstantOperand::cast(instr->length()));
+    if (instr->index()->IsConstantOperand()) {
+      int const_index = ToInteger32(LConstantOperand::cast(instr->index()));
+      int index = (const_length - const_index) + 1;
+      __ lw(result, MemOperand(arguments, index * kPointerSize));
+    } else {
+      Register index = ToRegister(instr->index());
+      __ li(at, Operand(const_length + 1));
+      __ Subu(result, at, index);
+      __ sll(at, result, kPointerSizeLog2);
+      __ Addu(at, arguments, at);
+      __ lw(result, MemOperand(at));
+    }
+  } else if (instr->index()->IsConstantOperand()) {
+    Register length = ToRegister(instr->length());
     int const_index = ToInteger32(LConstantOperand::cast(instr->index()));
-    int const_length = ToInteger32(LConstantOperand::cast(instr->length()));
-    int index = (const_length - const_index) + 1;
-    __ lw(result, MemOperand(arguments, index * kPointerSize));
+    int loc = const_index - 1;
+    if (loc != 0) {
+      __ Subu(result, length, Operand(loc));
+      __ sll(at, result, kPointerSizeLog2);
+      __ Addu(at, arguments, at);
+      __ lw(result, MemOperand(at));
+    } else {
+      __ sll(at, length, kPointerSizeLog2);
+      __ Addu(at, arguments, at);
+      __ lw(result, MemOperand(at));
+    }
   } else {
     Register length = ToRegister(instr->length());
     Register index = ToRegister(instr->index());
-    // There are two words between the frame pointer and the last argument.
-    // Subtracting from length accounts for one of them, add one more.
-    __ subu(length, length, index);
-    __ Addu(length, length, Operand(1));
-    __ sll(length, length, kPointerSizeLog2);
-    __ Addu(at, arguments, Operand(length));
-    __ lw(result, MemOperand(at, 0));
+    __ Subu(result, length, index);
+    __ Addu(result, result, 1);
+    __ sll(at, result, kPointerSizeLog2);
+    __ Addu(at, arguments, at);
+    __ lw(result, MemOperand(at));
   }
 }
 
 
 void LCodeGen::DoLoadKeyedExternalArray(LLoadKeyed* instr) {
   Register external_pointer = ToRegister(instr->elements());
   Register key = no_reg;
   ElementsKind elements_kind = instr->elements_kind();
   bool key_is_constant = instr->key()->IsConstantOperand();
   int constant_key = 0;
@@ skipping 2757 matching lines @@
   __ Subu(scratch, result, scratch);
   __ lw(result, FieldMemOperand(scratch,
                                 FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal