If a local variable is a constant, the subsequent code will be constant folded, but the local variable is not eliminated after constant folding.

It seems in Gen.visitVarDef, there is this line:
```
if (v.getConstValue() == null || varDebugInfo) {
```
to eliminate such local variables. Clearly, this apparently does not work.

For example, the following hashCode Java code

```java
package jdk.vm.ci.meta;

class AbstractProfiledItem {
    public int hashCode() {
        int prime = 31;
        int result = prime + Double.hashCode(probability);
        return prime * result + item.hashCode();
    }
}
```


The generated bytecode is

```
  public int hashCode();
    Code:
       0: bipush 31
       2: istore_1
       3: bipush 31
       5: aload_0
       6: getfield #20 // Field probability:D
       9: invokestatic #34 // Method java/lang/Double.hashCode:(D)I
      12: iadd
      13: istore_2
      14: bipush 31
      16: iload_2
      17: imul
      18: aload_0
      19: getfield #16 // Field item:Ljava/lang/Object;
      22: invokevirtual #38 // Method java/lang/Object.hashCode:()I
      25: iadd
      26: ireturn
```

The bytecodes 0 to 2 are not needed.