Re: pg_verify_checksums and -fno-strict-aliasing

I wrote:
> Some of these places might be performance-critical enough that adding
> a palloc/pfree cycle would not be nice. What I was considering doing
> was inventing something like
>
> typedef union PGAlignedBuffer
> {
> char data[BLCKSZ];
> double force_align;
> } PGAlignedBuffer;

Here's a proposed patch using that approach.

Although some of the places that were using "char buf[BLCKSZ]" variables
weren't doing anything that really requires better alignment, I made
almost all of them use PGAlignedBuffer variables anyway, on the grounds
that you typically get better memcpy speed for aligned than unaligned
transfers.

I also fixed a few places that were using the palloc solution, and
one that was actually doing hand-alignment of the pointer (ugh).
I didn't try to be thorough about getting rid of such pallocs,
just fix places that seemed likely to be performance-critical.

This needs to be back-patched as relevant, of course.

regards, tom lane