RFR: 8270179: Rename Amalloc_4

[Thomas Stuefe]

On Sun, 11 Jul 2021 23:27:33 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

> This renames Amalloc_4 to AmallocWords.  While I had to fix internal_malloc_4, which is a copy of Amalloc_4 (except with UseMallocOnly handling), I also made the change for
> JDK-8270217 Fix Arena::Amalloc to check for overflow better
> Tested with tier1 - all Oracle platforms and tier1-3 on linux-x64.

I'm not sure the alignment handling is correct. Either that or I don't understand the contract of the Amalloc... functions. 

I thought:

- Amalloc(x) -> allocate x bytes, align returned pointer to 64bit
- AmallocWords(x) -> allocate x bytes, align returned pointer to pointer size

?

Because the functions just align the given byte size (well, `Amalloc()` aligns automatically, `AmallocWords()` asserts). But that has no effect on the returned pointer.

Consider this, on 32bit:

1) AmallocWords(4) -> _hwm = 4
2) Amalloc(8) -> will return a pointer to offset 4, so not 64bit aligned.

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PR: https://git.openjdk.java.net/jdk/pull/4750