[PATCH][tree-ssa-address] Use simplify_gen_binary in gen_addr_rtx

[Kyrill Tkachov]

On 20/12/16 17:30, Richard Biener wrote:
> On December 20, 2016 5:01:19 PM GMT+01:00, Kyrill Tkachov <kyrylo.tkachov@foss.arm.com> wrote:
>> Hi all,
>>
>> The testcase in this patch generates bogus assembly for arm with -O1
>> -mfloat-abi=soft:
>>         strd    r4, [#0, r3]
>>
>> This is due to non-canonical RTL being generated during expansion:
>> (set (mem:DI (plus:SI (const_int 0 [0])
>>    (reg/f:SI 153)) [0 MEM[symbol: a, index: _26, offset: 0B]+0 S8 A64])
>>          (reg:DI 154))
>>
>> Note the (plus (const_int 0) (reg)). This is being generated in
>> gen_addr_rtx in tree-ssa-address.c
>> where it creates an explicit PLUS rtx through gen_rtx_PLUS, which
>> doesn't try to canonicalise its arguments
>> or simplify. The correct thing to do is to use simplify_gen_binary that
>> will handle all this properly.
> But it has to match up the validity check which passes down exactly the same RTL(?)  Or does this stem from propagation simplifying a MEM after IVOPTs?

You mean TARGET_LEGITIMATE_ADDRESS_P? Yes, it gets passed on to that, but the arm implementation of that
doesn't try to handle non-canonical RTL (plus (const0_rtx) (reg) is not canonical).
Or do you mean some other check?

Thanks,
Kyrill

>> I didn't change the other gen_rtx_PLUS calls in this function as their
>> results is later used in XEXP operations
>> that seem to rely on a PLUS expression being explicitly produced, but
>> this particular call doesn't, so it's okay
>> to change it. With this patch the sane assembly is generated:
>>          strd    r4, [r3]
>>
>> Bootstrapped and tested on arm-none-linux-gnueabihf, x86_64,
>> aarch64-none-linux-gnu.
>>
>> Ok for trunk?
>>
>> Thanks,
>> Kyrill
>>
>> 2016-12-20  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
>>
>>     * tree-ssa-address.c (gen_addr_rtx): Use simplify_gen_binary to add
>>      *addr to act_elem.
>>
>> 2016-12-20  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
>>
>>      * gcc.dg/20161219.c: New test.
>