[foreign-memaccess+abi] RFR: 8305087: MemoryLayout API checks should be more eager [v2]

[Per Minborg]

On Tue, 28 Mar 2023 16:56:39 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> This patch adds eager check on construction of sequence and group layouts. More specifically:
>> 
>> * sequenceLayout(L) is well-formed iff L.bitAlignment() <= L.bitSize()
>> * groupLayout(L1, … Ln) is well-formed iff for-each 1..n, offset(Li) % Li.bitAlignment() == 0
>> 
>> Moreover, this patch also validates the alignment parameter to calls of `MemoryLayout::withBitAlignment` on sequence and group layouts:
>> 
>> * sequenceLayout(L).withBitAlignment(a) is well-formed iff L.bitAlignment() <= a
>> * groupLayout(L1, ..., Ln).withBitAlignment(a) is well-formed iff max(L1.bitAlignment(), ...,  Ln.bitAlignment()) <= a
>> 
>> These checks prevent bad layouts from being constructed (either with factories, or with bad calls to `withBitAlignment`), w/o restricting the expressiveness of the memory layout API.
>> Moreover, since all layouts are now well-formed by construction, we no longer need lazy checks when creating a deferefence var handle.
>
> Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Update src/java.base/share/classes/java/lang/foreign/GroupLayout.java
>   
>   Co-authored-by: Jorn Vernee <JornVernee at users.noreply.github.com>

src/java.base/share/classes/jdk/internal/foreign/layout/AbstractGroupLayout.java line 143:

> 141:             long size = 0;
> 142:             for (MemoryLayout elem : elems) {
> 143:                 if (this == STRUCT && (size % elem.bitAlignment() != 0)) {

We might drop `sizeOp` and instead have two different `sizeof` implementations in a more OO style.

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PR Review Comment: https://git.openjdk.org/panama-foreign/pull/824#discussion_r1151505440