From 5d7e335afd451c2c9980738a9610fdf2c7fe9943 Mon Sep 17 00:00:00 2001
From: "palfia@homejinni.com"
 <palfia@homejinni.com@ce2b1a6d-e550-0410-aec6-3dcde31c8c00>
Date: Mon, 22 Apr 2013 22:45:34 +0000
Subject: [PATCH] MIPS: Improvements in lithium code generation. Recognizing if
 some operands are constants, we can often save on registers and instructions.

Port r14364 (2819e5ee)

BUG=

Review URL: https://codereview.chromium.org/14159015

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14383 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
---
 src/mips/lithium-codegen-mips.cc | 26 +++++++++++++++++---------
 src/mips/lithium-mips.cc         | 11 +++++++++--
 2 files changed, 26 insertions(+), 11 deletions(-)

diff --git a/src/mips/lithium-codegen-mips.cc b/src/mips/lithium-codegen-mips.cc
index 9ae5132cf..ca74800ff 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.
+    __ subu(length, length, index);
+    __ Addu(length, length, Operand(1));
+    __ sll(length, length, kPointerSizeLog2);
+    __ Addu(at, arguments, Operand(length));
+    __ lw(result, MemOperand(at, 0));
+  }
 }
 
 
diff --git a/src/mips/lithium-mips.cc b/src/mips/lithium-mips.cc
index fb8826b7f..41487f6d7 100644
--- a/src/mips/lithium-mips.cc
+++ b/src/mips/lithium-mips.cc
@@ -2340,8 +2340,15 @@ LInstruction* LChunkBuilder::DoArgumentsObject(HArgumentsObject* instr) {
 LInstruction* LChunkBuilder::DoAccessArgumentsAt(HAccessArgumentsAt* instr) {
   info()->MarkAsRequiresFrame();
   LOperand* args = UseRegister(instr->arguments());
-  LOperand* length = UseTempRegister(instr->length());
-  LOperand* index = UseRegister(instr->index());
+  LOperand* length;
+  LOperand* index;
+  if (instr->length()->IsConstant() && instr->index()->IsConstant()) {
+    length = UseRegisterOrConstant(instr->length());
+    index = UseOrConstant(instr->index());
+  } else {
+    length = UseTempRegister(instr->length());
+    index = Use(instr->index());
+  }
   return DefineAsRegister(new(zone()) LAccessArgumentsAt(args, length, index));
 }
 
-- 
2.34.1