RFR: 8309502: RISC-V: String.indexOf intrinsic may produce misaligned memory loads

[Fei Yang]

On Wed, 7 Jun 2023 07:54:49 GMT, Vladimir Kempik <vkempik at openjdk.org> wrote:

> See, this part of algo is misaligned
> 
> ```
>  bind(CH1_LOOP);
>     add(tmp3, haystack, hlen_neg);
>     (this->*load_2chr)(ch2, Address(tmp3), noreg);
>     beq(ch1, ch2, MATCH);
>     add(hlen_neg, hlen_neg, haystack_chr_size);
>     blez(hlen_neg, CH1_LOOP);
> ```
> 
> this becomes:
> 
> ```
> CH1_LOOP: add t4, a1, a2
> lhu t1, 0(t4)
> beg t0, t1, 0xMATCH
> addi a2, a2, 1
> blez a2, CH1_LOOP
> ```
> 
> so we load halfword on each iteration from address (a1+a2), and while a1 is constant, a2 is incrementing by 1 each step, so every other load is misaligned.

I see it now. Thanks. Then I am expecting that we could also have similar issue for the `if (needle_con_cnt == 4)` case in the same function where we do `load_4chr` incrementally with 1 byte step when `isLL` variable is true, right?

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PR Comment: https://git.openjdk.org/jdk/pull/14320#issuecomment-1580190910