X64: Abstract indexing by a smi to the macro assembler.

src/x64/macro-assembler-x64.cc

Index: src/x64/macro-assembler-x64.cc
diff --git a/src/x64/macro-assembler-x64.cc b/src/x64/macro-assembler-x64.cc
index c3a723f89f4192ce86db88090883d7a09bc8e5eb..bd9d20a7d456a2fe9009c2e7dce0ddc23c1c8209 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -1092,6 +1092,51 @@ void MacroAssembler::SelectNonSmi(Register dst,
 }
 
 
+SmiIndex MacroAssembler::SmiToIndex(Register dst, Register src, int shift) {
+  ASSERT(is_uint6(shift));
+  if (shift == 0) {  // times_1.
+    SmiToInteger32(dst, src);
+    return SmiIndex(dst, times_1);
+  }
+  if (shift <= 4) {  // 2 - 16 times multiplier.
+    return SmiIndex(src, static_cast<ScaleFactor>(shift - kSmiTagSize));

[William Hesse, 2009/09/15 10:12:09]

How are we making sure that src is zero-extended here?  Won't this cause errors?
Also, shouldn't we check 0 <= shift-kSmiTagSize < 4 ?

[Lasse Reichstein, 2009/09/15 10:39:08]

We should make sure. I'll add a movel(dst, src).

This code assumes the value of kSmiTagSize is 1. If that changes, all the
abstraced smi operations must be checked.

+  }
+  // Shift by shift-kSmiTagSize.
+  if (!dst.is(src)) {
+    movl(dst, src);
+  }
+  shl(dst, Immediate(shift - kSmiTagSize));
+  return SmiIndex(dst, times_1);
+}
+
+
+SmiIndex MacroAssembler::SmiToNegativeIndex(Register dst,
+                                            Register src,
+                                            int shift) {
+  // Register src holds a positive smi.
+  ASSERT(is_uint6(shift));
+  if (shift == 0) {  // times_1.
+    SmiToInteger32(dst, src);
+    neg(dst);
+    return SmiIndex(dst, times_1);
+  }
+  if (shift <= 4) {  // 2 - 16 times multiplier is handled using ScaleFactor.
+    if (!dst.is(src)) {
+      movl(dst, src);
+    }
+    neg(dst);
+    return SmiIndex(dst, static_cast<ScaleFactor>(shift - kSmiTagSize));
+  }
+  // Shift by shift-kSmiTagSize.
+  if (!dst.is(src)) {
+    movl(dst, src);
+  }
+  neg(dst);
+  shl(dst, Immediate(shift - kSmiTagSize));
+  return SmiIndex(dst, times_1);
+}
+
+
 
 bool MacroAssembler::IsUnsafeSmi(Smi* value) {
   return false;