MIPS: Improvements in lithium code generation. Recognizing if some operands are constants, we can o…

src/mips/lithium-codegen-mips.cc

Index: src/mips/lithium-codegen-mips.cc
diff --git a/src/mips/lithium-codegen-mips.cc b/src/mips/lithium-codegen-mips.cc
index 9ae5132cf3bb8140c5b8108fb366298e2819e9cb..7a374d2de7cb5c73111221e7cecd3045cdfa7d59 100644
--- a/src/mips/lithium-codegen-mips.cc
+++ b/src/mips/lithium-codegen-mips.cc
@@ -2873,16 +2873,24 @@ void LCodeGen::DoLoadExternalArrayPointer(
 
 void LCodeGen::DoAccessArgumentsAt(LAccessArgumentsAt* instr) {
   Register arguments = ToRegister(instr->arguments());
-  Register length = ToRegister(instr->length());
-  Register index = ToRegister(instr->index());
   Register result = ToRegister(instr->result());
-  // 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));
+  if (instr->length()->IsConstantOperand() &&
+      instr->index()->IsConstantOperand()) {
+    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));
+  } 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.

[Paul Lind, 2013/04/22 21:49:22]

nit: comma after word 'them':
...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));
+  }
 }