X64: Make the ToBoolean inline code do even less if the value is known to be a smi.

src/x64/codegen-x64.cc

Index: src/x64/codegen-x64.cc
diff --git a/src/x64/codegen-x64.cc b/src/x64/codegen-x64.cc
index 0c4cd16ceed6d70646659ffda142dddf57ab8078..09deda8eb88d9e7c3ea5d601e7489204e8863c0b 100644
--- a/src/x64/codegen-x64.cc
+++ b/src/x64/codegen-x64.cc
@@ -5342,13 +5342,18 @@ void CodeGenerator::ToBoolean(ControlDestination* dest) {
     }
     // Smi => false iff zero.
     __ SmiCompare(value.reg(), Smi::FromInt(0));
-    dest->false_target()->Branch(equal);
-    Condition is_smi = masm_->CheckSmi(value.reg());
-    dest->true_target()->Branch(is_smi);
-    __ xorpd(xmm0, xmm0);
-    __ ucomisd(xmm0, FieldOperand(value.reg(), HeapNumber::kValueOffset));
-    value.Unuse();
-    dest->Split(not_zero);
+    if (value.is_smi()) {
+      value.Unuse();
+      dest->Split(not_zero);
+    } else {
+      dest->false_target()->Branch(equal);

[William Hesse, 2010/06/29 10:50:10]

Why not also have a case for if value.is_double()?

[Lasse Reichstein, 2010/06/29 14:13:30]

I doubt it will happen in practice that we convert a value to boolean that we
*know* is a double.

I don't know whether we would want to do something for the known string case.
Again, I don't expect known string operation results to be used as booleans
much.

Maybe we should add a counter for the other special cases and see if they are
hit.

+      Condition is_smi = masm_->CheckSmi(value.reg());
+      dest->true_target()->Branch(is_smi);
+      __ xorpd(xmm0, xmm0);
+      __ ucomisd(xmm0, FieldOperand(value.reg(), HeapNumber::kValueOffset));
+      value.Unuse();
+      dest->Split(not_zero);
+    }
   } else {
     // Fast case checks.
     // 'false' => false.