我们如何知道要设置多少堆？

Question

I'm trying to convert Java to an intermediate language and am in the process of figuring out how the intermediate language works.

I have the original Java code: http://cs.ucla.edu/classes/spring11/cs132/cs132/mj/Factorial.java

And I have the Intermediate Code representation (VAPOR): http://cs.ucla.edu/classes/spring11/cs132/kannan/vapor-examples/Factorial.vapor

Here's another set: in Java: http://cs.ucla.edu/classes/spring11/cs132/cs132/mj/BubbleSort.java

In VAPOR: http://cs.ucla.edu/classes/spring11/cs132/kannan/vapor-examples/BubbleSort.vapor

My question is, all of the VAPOR code has t.0 = HeapAllocZ(x) (where x is an int ). I'm wondering how the converter determines the heap size needs to be size x . In Factorial.vapor , it's set to 4 . In BubbleSort.vapor , it's set to 12 .

Thanks!

Answer 1

It looks like the HeapAlloc is based on the size of the structure you are creating (assuming 4 and 12 are byte values). I would think that looking at the variables your data structure uses, and counting the number of bytes those variables sum to would give you the number being allocated.

Answer 2

If you notice, the Java version of Factorial has no data members. The Java version of BubbleSort has two 4-byte ints (8 bytes total).

Presumably the "overhead" of an object is 4 bytes (the size of a pointer to the class object).

So Factorial has an object size of 4 and BubbleSort has an object size of 12.