[turbofan] Add proper conversion operators for int32<->int64.

src/compiler/machine-operator.h

Index: src/compiler/machine-operator.h
diff --git a/src/compiler/machine-operator.h b/src/compiler/machine-operator.h
index 219831c0cfedd92986ed4c4d8dd84cf4f3ee5b17..4b2d3417613555748201384ae10cdfdec09db21f 100644
--- a/src/compiler/machine-operator.h
+++ b/src/compiler/machine-operator.h
@@ -121,19 +121,22 @@ class MachineOperatorBuilder {
   Operator* Int64LessThan() { BINOP(Int64LessThan); }
   Operator* Int64LessThanOrEqual() { BINOP(Int64LessThanOrEqual); }
 
-  Operator* ConvertInt32ToInt64() { UNOP(ConvertInt32ToInt64); }
-  Operator* ConvertInt64ToInt32() { UNOP(ConvertInt64ToInt32); }
-
   // Convert representation of integers between float64 and int32/uint32.
   // The precise rounding mode and handling of out of range inputs are *not*
   // defined for these operators, since they are intended only for use with
   // integers.
-  // TODO(titzer): rename ConvertXXX to ChangeXXX in machine operators.
   Operator* ChangeInt32ToFloat64() { UNOP(ChangeInt32ToFloat64); }
   Operator* ChangeUint32ToFloat64() { UNOP(ChangeUint32ToFloat64); }
   Operator* ChangeFloat64ToInt32() { UNOP(ChangeFloat64ToInt32); }
   Operator* ChangeFloat64ToUint32() { UNOP(ChangeFloat64ToUint32); }
 
+  // Sign/zero extend int32/uint32 to int64/uint64.
+  Operator* ChangeInt32ToInt64() { UNOP(ChangeInt32ToInt64); }
+  Operator* ChangeUint32ToUint64() { UNOP(ChangeUint32ToUint64); }
+
+  // Truncate the high order bits and convert the remaining bits to int32.
+  Operator* TruncateInt64ToInt32() { UNOP(TruncateInt64ToInt32); }
+
   // Floating point operators always operate with IEEE 754 round-to-nearest.
   Operator* Float64Add() { BINOP_C(Float64Add); }
   Operator* Float64Sub() { BINOP(Float64Sub); }