> This patch fixes `Utils::checkElementAlignment` to do the right thing for > _all_ layouts. > > The current implementation is broken, as it only works correctly when the > input layout is a value layout. > Since value layouts have a size that is a power of two (and size all layouts > have alignment that is also a power of two), then verifying that `size > > alignment` works well. > > But if the input layout is some other layout (e.g. a `StructLayout`), this > "power of two" assumption no longer holds. E.g. we can have a layout whose > size is 48, and whose alignment is 32. While 48 is clearly bigger than 32, > such a layout is still not suitable to be used as an element layout in a > sequence. > > The fix is to provide two overloads for `Utils::checkElementAlignment` - one > which works on `ValueLayout` and another which works on any `MemoryLayout`. > The `ValueLayout` version works as before (so performance is not affected). > The `MemoryLayout` variant would perform a full check using the `%` operator. > Currently we only use this when creating a new sequence layout and when > creating a stream out of a memory segment, so I'm not worried about potential > performance regressions. > > I've fixed the javadoc so that the various `@throws` clauses in the affected > methods reflect the correct behavior. > > Finally, I've made the existing alignment/layout tests a bit more robust, by > also adding pair-wise combinations of layouts, wrapped in a struct/union. > This does generate illegal layout cases which would not have been detected > w/o this patch.
Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision: Address review comments (add assert for power of two) ------------- Changes: - all: https://git.openjdk.org/jdk/pull/13784/files - new: https://git.openjdk.org/jdk/pull/13784/files/1f2fd4b0..682bfaf1 Webrevs: - full: https://webrevs.openjdk.org/?repo=jdk&pr=13784&range=01 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13784&range=00-01 Stats: 9 lines in 2 files changed: 7 ins; 0 del; 2 mod Patch: https://git.openjdk.org/jdk/pull/13784.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/13784/head:pull/13784 PR: https://git.openjdk.org/jdk/pull/13784
