On Sat, Jul 9, 2011 at 23:31, H.J. Lu <hjl.to...@gmail.com> wrote: > On Sat, Jul 9, 2011 at 2:18 PM, Paolo Bonzini <bonz...@gnu.org> wrote: >> On 07/05/2011 04:27 PM, H.J. Lu wrote: >>>> >>>> diff --git a/gcc/explow.c b/gcc/explow.c >>>> index 7387dad..b343bf8 100644 >>>> --- a/gcc/explow.c >>>> +++ b/gcc/explow.c >>>> @@ -383,18 +383,13 @@ convert_memory_address_addr_space (enum >>>> machine_mode to_mode ATTRIBUTE_UNUSED, >>>> >>>> case PLUS: >>>> case MULT: >>>> - /* For addition we can safely permute the conversion and addition >>>> - operation if one operand is a constant and converting the >>>> constant >>>> - does not change it or if one operand is a constant and we are >>>> - using a ptr_extend instruction (POINTERS_EXTEND_UNSIGNED< 0). >>>> - We can always safely permute them if we are making the address >>>> - narrower. */ >>>> + /* For addition we safely permute the conversion and addition >>>> + operation if one operand is a constant since we can't generate >>>> + new instructions. We can always safely permute them if we are >>>> + making the address narrower. */ >>>> if (GET_MODE_SIZE (to_mode)< GET_MODE_SIZE (from_mode) >>>> || (GET_CODE (x) == PLUS >>>> -&& CONST_INT_P (XEXP (x, 1)) >>>> -&& (XEXP (x, 1) == convert_memory_address_addr_space >>>> - (to_mode, XEXP (x, 1), as) >>>> - || POINTERS_EXTEND_UNSIGNED< 0))) >>>> +&& CONST_INT_P (XEXP (x, 1)))) >>>> return gen_rtx_fmt_ee (GET_CODE (x), to_mode, >>>> convert_memory_address_addr_space >>>> (to_mode, XEXP (x, 0), as), >> >> This does not seem safe to me. > > The current code is broken for x32. See: > > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47727 > > We can't generate any new instructions. Do you have any suggestions.
By "safe" I mean that the new condition might be too wide and generate wrong code. Richard is definitely right in comment 6, generating new code in simplify-rtx is a no-no (see its usage of gen_lowpart_no_emit). Paolo
