https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63156
--- Comment #4 from Carrot <carrot at google dot com> ---
In function df_uses_record, we have:
...
case PRE_DEC:
case POST_DEC:
case PRE_INC:
case POST_INC:
case PRE_MODIFY:
case POST_MODIFY:
gcc_assert (!DEBUG_INSN_P (insn_info->insn));
/* Catch the def of the register being modified. */
df_ref_record (DF_REF_REGULAR, collection_rec, XEXP (x, 0), &XEXP (x, 0),
bb, insn_info,
DF_REF_REG_DEF,
flags | DF_REF_READ_WRITE | DF_REF_PRE_POST_MODIFY);
/* ... Fall through to handle uses ... */
default:
break;
}
/* Recursively scan the operands of this expression. */
{
const char *fmt = GET_RTX_FORMAT (code);
int i;
for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
{
if (fmt[i] == 'e')
{
/* Tail recursive case: save a function call level. */
if (i == 0)
{
loc = &XEXP (x, 0);
goto retry;
}
df_uses_record (collection_rec, &XEXP (x, i), ref_type,
bb, insn_info, flags);
}
...
For a AUTOINC rtl expression, we create two refs, one def and one use, but only
the def gets the flag DF_REF_READ_WRITE, the use doesn't have this flag.
While in web_main, it checks only use refs, but the use ref doesn't have the
flag DF_REF_READ_WRITE, so it can't actually catch the AUTOINC cases, and does
wrong renaming.
