Some improvements in register usage in lithium compilation of LoadKeyed/StoreKeyed operations.

src/arm/lithium-arm.cc

Index: src/arm/lithium-arm.cc
diff --git a/src/arm/lithium-arm.cc b/src/arm/lithium-arm.cc
index bcd43a5e6a8adeb9c75b1ea95412b239879da038..fa17e6ad15f8ad8f7890e6cc649bcd01972dae10 100644
--- a/src/arm/lithium-arm.cc
+++ b/src/arm/lithium-arm.cc
@@ -1875,7 +1875,15 @@ LInstruction* LChunkBuilder::DoLoadKeyed(HLoadKeyed* instr) {
         (instr->representation().IsDouble() &&
          ((elements_kind == EXTERNAL_FLOAT_ELEMENTS) ||
           (elements_kind == EXTERNAL_DOUBLE_ELEMENTS))));
-    LOperand* external_pointer = UseRegister(instr->elements());
+
+    LOperand* external_pointer;
+    // We only need a long-lived register for constant keys with an offset
+    if (instr->key()->IsConstant() && instr->index_offset() != 0) {
+      external_pointer = UseRegister(instr->elements());
+    } else {
+      external_pointer = UseRegisterAtStart(instr->elements());

[danno, 2012/11/07 22:34:38]

I don't see the difference in these two case in the codegen file, and in
practice since there are no temp registers, it probably doesn't make a
difference (I am not 100% sure whether UseRegister overlaps with the return
register. If it really doesn't make a difference, UseRegister all the time
probably will simplify the code.

[mvstanton, 2012/11/09 09:43:13]

Done.

+    }
+
     result = new(zone()) LLoadKeyed(external_pointer, key);
   }
 
@@ -1899,32 +1907,22 @@ LInstruction* LChunkBuilder::DoLoadKeyedGeneric(HLoadKeyedGeneric* instr) {
 
 
 LInstruction* LChunkBuilder::DoStoreKeyed(HStoreKeyed* instr) {
-  ElementsKind elements_kind = instr->elements_kind();
-  bool needs_write_barrier = instr->NeedsWriteBarrier();
-  LOperand* key = needs_write_barrier
-      ? UseTempRegister(instr->key())
-      : UseRegisterOrConstantAtStart(instr->key());
-  bool val_is_temp_register =
-      elements_kind == EXTERNAL_PIXEL_ELEMENTS ||
-      elements_kind == EXTERNAL_FLOAT_ELEMENTS;
-  LOperand* val = val_is_temp_register || needs_write_barrier
-      ? UseTempRegister(instr->value())
-      : UseRegister(instr->value());
+  LOperand* elements = UseRegisterAtStart(instr->elements());
+  LOperand* key;
+  LOperand* val;
+  if (instr->NeedsWriteBarrier()) {
+    key = UseTempRegister(instr->key());
+    val = UseTempRegister(instr->value());
+  } else {
+    key = UseRegisterOrConstantAtStart(instr->key());
+    val = UseRegisterAtStart(instr->value());
+  }
 
-  LStoreKeyed* result = NULL;
+#ifdef DEBUG
   if (!instr->is_external()) {
     ASSERT(instr->elements()->representation().IsTagged());
-
-    LOperand* object = NULL;
-    if (instr->value()->representation().IsDouble()) {
-      object = UseRegisterAtStart(instr->elements());
-    } else {
-      ASSERT(instr->value()->representation().IsTagged());
-      object = UseTempRegister(instr->elements());
-    }
-
-    result = new(zone()) LStoreKeyed(object, key, val);
   } else {
+    ElementsKind elements_kind = instr->elements_kind();
     ASSERT(
         (instr->value()->representation().IsInteger32() &&
          (elements_kind != EXTERNAL_FLOAT_ELEMENTS) &&
@@ -1933,11 +1931,10 @@ LInstruction* LChunkBuilder::DoStoreKeyed(HStoreKeyed* instr) {
          ((elements_kind == EXTERNAL_FLOAT_ELEMENTS) ||
           (elements_kind == EXTERNAL_DOUBLE_ELEMENTS))));
     ASSERT(instr->elements()->representation().IsExternal());
-
-    LOperand* external_pointer = UseRegister(instr->elements());
-    result = new(zone()) LStoreKeyed(external_pointer, key, val);
   }
+#endif
 
+  LStoreKeyed* result = new(zone()) LStoreKeyed(elements, key, val);
   ASSERT(result != NULL);
   return result;
 }