MIPS: Optimize AccessArgumentsAt.

Port r17923 (837f909)

Original commit message:
Optimize register constraints and code generated for AccessArgumentsAt Lithium instruction.

BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/79143007

Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@17977 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

diff --git a/src/mips/lithium-codegen-mips.cc b/src/mips/lithium-codegen-mips.cc
index e40021d..5a8249e 100644 (file)
--- a/src/mips/lithium-codegen-mips.cc
+++ b/src/mips/lithium-codegen-mips.cc
@@ -3037,22 +3037,44 @@ void LCodeGen::DoLoadExternalArrayPointer(
 void LCodeGen::DoAccessArgumentsAt(LAccessArgumentsAt* instr) {
   Register arguments = ToRegister(instr->arguments());
   Register result = ToRegister(instr->result());
-  if (instr->length()->IsConstantOperand() &&
-      instr->index()->IsConstantOperand()) {
-    int const_index = ToInteger32(LConstantOperand::cast(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.
+  if (instr->length()->IsConstantOperand()) {
     int const_length = ToInteger32(LConstantOperand::cast(instr->length()));
-    int index = (const_length - const_index) + 1;
-    __ lw(result, MemOperand(arguments, index * kPointerSize));
+    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 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));
   }
 }
 

diff --git a/src/mips/lithium-mips.cc b/src/mips/lithium-mips.cc
index fa653c6..34e5838 100644 (file)
--- a/src/mips/lithium-mips.cc
+++ b/src/mips/lithium-mips.cc
@@ -2459,15 +2459,8 @@ LInstruction* LChunkBuilder::DoCapturedObject(HCapturedObject* instr) {
 LInstruction* LChunkBuilder::DoAccessArgumentsAt(HAccessArgumentsAt* instr) {
   info()->MarkAsRequiresFrame();
   LOperand* args = UseRegister(instr->arguments());
-  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 = UseRegisterAtStart(instr->index());
-  }
+  LOperand* length = UseRegisterOrConstantAtStart(instr->length());
+  LOperand* index = UseRegisterOrConstantAtStart(instr->index());
   return DefineAsRegister(new(zone()) LAccessArgumentsAt(args, length, index));
 }