MIPS: Fixed several bugs in SubStringStub::Generate.

src/mips/code-stubs-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 6043 matching lines @@
   static const int kStringOffset = 2 * kPointerSize;
 
   __ lw(a2, MemOperand(sp, kToOffset));
   __ lw(a3, MemOperand(sp, kFromOffset));
   STATIC_ASSERT(kFromOffset == kToOffset + 4);
   STATIC_ASSERT(kSmiTag == 0);
   STATIC_ASSERT(kSmiTagSize + kSmiShiftSize == 1);
 
   // Utilize delay slots. SmiUntag doesn't emit a jump, everything else is
   // safe in this case.
-  __ UntagAndJumpIfSmi(a2, a2, &runtime);
-  __ UntagAndJumpIfSmi(a3, a3, &runtime);
-
+  __ UntagAndJumpIfNotSmi(a2, a2, &runtime);
+  __ UntagAndJumpIfNotSmi(a3, a3, &runtime);
   // Both a2 and a3 are untagged integers.
 
   __ Branch(&runtime, lt, a3, Operand(zero_reg));  // From < 0.
 
-  __ subu(a2, t5, a3);
-  __ Branch(&runtime, gt, a3, Operand(t5));  // Fail if from > to.
+  __ Branch(&runtime, gt, a3, Operand(a2));  // Fail if from > to.
+  __ Subu(a2, a2, a3);
 
   // Make sure first argument is a string.
   __ lw(v0, MemOperand(sp, kStringOffset));
-  __ Branch(&runtime, eq, v0, Operand(kSmiTagMask));
-
+  __ JumpIfSmi(v0, &runtime);
   __ lw(a1, FieldMemOperand(v0, HeapObject::kMapOffset));
   __ lbu(a1, FieldMemOperand(a1, Map::kInstanceTypeOffset));
-  __ And(t4, v0, Operand(kIsNotStringMask));
+  __ And(t0, a1, Operand(kIsNotStringMask));
 
-  __ Branch(&runtime, ne, t4, Operand(zero_reg));
+  __ Branch(&runtime, ne, t0, Operand(zero_reg));
 
   // Short-cut for the case of trivial substring.
   Label return_v0;
   // v0: original string
   // a2: result string length
   __ lw(t0, FieldMemOperand(v0, String::kLengthOffset));
   __ sra(t0, t0, 1);
   __ Branch(&return_v0, eq, a2, Operand(t0));
 
 
@@ skipping 1546 matching lines @@
   __ Ret(USE_DELAY_SLOT);
   __ mov(v0, a0);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_MIPS