[Bug target/93808] [9 Regression] [SH] Ruby crashes with 'Illegal Instruction' with -fcrossjumping

[olegendo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93808

--- Comment #18 from Oleg Endo <olegendo at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #17)
> In the original code we have:
>  if ((uintptr_t)p % 4) {
>      int l = 4 - (uintptr_t)p % 4;
>      p += l;
>      switch (l) {
> 
> l range should be 0...3


Ha!  This code is an autostereogram.  You gotta stare at it until something
comes out of it (or falls in) ...

  if (0 || e - p >= 4)
  {
    if ((uintptr_t)p % 4)
    {
      // when here, p % 4 is never zero.

      // thus, l = 4 - {3|2|1}
      int l = 4 - (uintptr_t)p % 4;

However, that's not where it crashes.  It's in the second switch statement.  I
assume that's because it's never supposed to get there, but it does.

What the code does is trying to walk an array of bytes in 4-byte steps.  For
that it potentially steps 0...3 bytes to get a 4-byte aligned pointer 'p', then
does the 4-byte steps in the for loop, then does  the remaining 0...3 bytes
after the loop.

Perhaps this line

    p = (const char *)s;

somehow results in wrong code with p not being updated correctly, and then (e -
p) is not in the range {3|2|1|0} as the code expects.