HLoadKeyed for Smis optimized for x64

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
diff --git a/src/x64/lithium-codegen-x64.cc b/src/x64/lithium-codegen-x64.cc
index 7c9949a1fad8da5b441e7ecd79d96ab41dbea073..e8287e2aaec1fdf907b7d4fb670e5da30ac95c64 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -3053,6 +3053,7 @@ void LCodeGen::DoLoadKeyedFixedDoubleArray(LLoadKeyed* instr) {
 
 
 void LCodeGen::DoLoadKeyedFixedArray(LLoadKeyed* instr) {
+  HLoadKeyed* hinstr = instr->hydrogen();
   Register result = ToRegister(instr->result());
   LOperand* key = instr->key();
   if (!key->IsConstantOperand()) {
@@ -3062,24 +3063,34 @@ void LCodeGen::DoLoadKeyedFixedArray(LLoadKeyed* instr) {
     // gets replaced during bound check elimination with the index
     // argument to the bounds check, which can be tagged, so that
     // case must be handled here, too.
-    if (instr->hydrogen()->IsDehoisted()) {
+    if (hinstr->IsDehoisted()) {
       // Sign extend key because it could be a 32 bit negative value
       // and the dehoisted address computation happens in 64 bits
       __ movsxlq(key_reg, key_reg);
     }
   }
 
-  // Load the result.
-  __ movq(result,
+  bool requires_hole_check = hinstr->RequiresHoleCheck();
+  int offs = FixedArray::kHeaderSize - kHeapObjectTag;

[Toon Verwaest, 2013/12/09 13:47:23]

Please write out variable names: "offset".

[Igor Sheludko, 2013/12/09 17:27:06]

Done.

+  Representation representation = hinstr->representation();
+
+  if (hinstr->type().IsSmi() && representation.IsInteger32()) {

[Toon Verwaest, 2013/12/09 13:47:23]

Why check for hinstr->type().IsSmi()? You should only get to
representation.IsInteger32() if you converted a smi-load into an int32 load.

[Igor Sheludko, 2013/12/09 17:27:06]

We can't rely only on IsInteger32() case since we can get an int32
representation for external arrays. We dicussed this and decided that it is
better to check elements' kind against FAST_SMI_ELEMENTS.

+    ASSERT(!requires_hole_check);
+    // Read int value directly from upper half of the smi.
+    offs += kPointerSize / 2;

[Toon Verwaest, 2013/12/09 13:47:23]

Isn't there a kSmiTagSize you can use? You just want to jump over the smi-tag.

[Igor Sheludko, 2013/12/09 17:27:06]

kSmiTagSize is a number of bits, so we can't use it here, but I'll add an assert
instead:
STATIC_ASSERT(kSmiTagSize + kSmiShiftSize == 32);

+  }
+
+  __ Load(result,
           BuildFastArrayOperand(instr->elements(),
                                 key,
                                 FAST_ELEMENTS,
-                                FixedArray::kHeaderSize - kHeapObjectTag,
-                                instr->additional_index()));
+                                offs,
+                                instr->additional_index()),
+          representation);
 
   // Check for the hole value.
-  if (instr->hydrogen()->RequiresHoleCheck()) {
-    if (IsFastSmiElementsKind(instr->hydrogen()->elements_kind())) {
+  if (requires_hole_check) {
+    if (IsFastSmiElementsKind(hinstr->elements_kind())) {
       Condition smi = __ CheckSmi(result);
       DeoptimizeIf(NegateCondition(smi), instr->environment());
     } else {