https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62262
amker at gcc dot gnu.org changed:
What |Removed |Added
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CC| |amker at gcc dot gnu.org
--- Comment #2 from amker at gcc dot gnu.org ---
(In reply to Andrew Pinski from comment #1)
> (insn 27 26 40 5 (set (reg:SI 73 [ D.2590 ])
> (and:SI (ashift:SI (reg/v:SI 74 [ value ])
> (const_int 32 [0x20]))
> (const_int 8388607 [0x7fffff]))) t7.c:13 611
> {*andim_ashiftsi_bfiz}
> (expr_list:REG_DEAD (reg/v:SI 74 [ value ])
> (nil)))
>
> Confirmed.
>
> "exact_log2 ((INTVAL (operands[3]) >> INTVAL (operands[2])) + 1) >= 0
> && (INTVAL (operands[3]) & ((1 << INTVAL (operands[2])) - 1)) == 0"
>
>
> In fact we invoke undefined behavior inside the compiler too due to the
> shift there.
Since it's undefined code, how should we handle it in GCC? Should we give
warning messages as accurate as possible? But that sounds impractical either,
since "value << 1" and "value <<= zeros" could be undefined too.
