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Re: PING: PATCH [4/n]: Prepare x32: Permute the conversion and addition if one operand is a constant
On Sat, Jul 9, 2011 at 23:31, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Sat, Jul 9, 2011 at 2:18 PM, Paolo Bonzini <bonzini@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