[Bug rtl-optimization/83565] New: RTL combine pass breaks shift result (at least on ia64)

[slyfox at inbox dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83565

            Bug ID: 83565
           Summary: RTL combine pass breaks shift result (at least on
                    ia64)
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: slyfox at inbox dot ru
  Target Milestone: ---

Created attachment 42959
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42959&action=edit
a.c

Original but was seen as an openssl DES testsuite failure.

Below is a distilled example that yields differetn results
when built as -O0 vs. -O1 built:

#include <stdio.h>

/*
$ gcc -O0 a.c -o a-O0 && ./a-O0 > o0
$ gcc -O1 a.c -o a-O1 && ./a-O1 > o1
$ diff -U0 o0 o1

-off>>: 7fffffff
+off>>: ffffffff
*/

typedef unsigned int u32;

u32 bug (u32 * result) __attribute__((noinline));
u32 bug (u32 * result)
{
    // non-static and non-volatile to inhibit constant propagation
    volatile u32 ss = 0xFFFFffff;
    volatile u32 d  = 0xEEEEeeee;
    u32 tt = d & 0x00800000;
    u32 r  = tt << 8;

    // rotate
    r = (r >> 31)
      | (r <<  1);

    u32 u = r^ss;
    u32 off = u >> 1;

    // seemingly unrelated but bug-triggering side-effect
    *result = tt;
    return off;
}

int main() {
    u32 l;
    u32 off = bug(&l);
    printf ("off>>: %08x\n", off);
    return 0;
}