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Re: IVOPT improvement patch
- From: Xinliang David Li <davidxl at google dot com>
- To: GCC Patches <gcc-patches at gcc dot gnu dot org>
- Cc: Richard Guenther <richard dot guenther at gmail dot com>, Pat Haugen <pthaugen at us dot ibm dot com>, Zdenek Dvorak <rakdver at kam dot mff dot cuni dot cz>, "H.J. Lu" <hjl dot tools at gmail dot com>
- Date: Mon, 2 Aug 2010 14:23:36 -0700
- Subject: Re: IVOPT improvement patch
- References: <20100525235926.GA3326@kam.mff.cuni.cz> <AANLkTikGZ-LQGCIlr4K1GIhILtRsTI2MNCPMP5cazPkG@mail.gmail.com> <20100527075632.GA12991@kam.mff.cuni.cz> <AANLkTimY4icwv57CMowcV7UtOXGU2Yqfmg5Z0nwsRSDe@mail.gmail.com> <20100528085052.GA3423@kam.mff.cuni.cz> <AANLkTikNxYZLO3egDnljShqbfFydKrZU70xw8aG6Mfbo@mail.gmail.com> <20100529152243.GA18706@kam.mff.cuni.cz> <AANLkTinXyF9GhrcZxjohiP3ypcfpqgicv4KnegvYWwYR@mail.gmail.com> <20100529191446.GA3996@kam.mff.cuni.cz> <AANLkTimJoc5EeFxvTo731fpE4rGYdLgbOI5l0q9GbG33@mail.gmail.com> <20100604105451.GB5105@kam.mff.cuni.cz> <AANLkTi=iM78LxLm=2R7QxObC0NE0ZkG3YatCnwXHaSpM@mail.gmail.com> <AANLkTinnMVXcAR0eo7LpBioGoC8dT8gR7hD-gfa1vCm2@mail.gmail.com> <AANLkTi=g2zTrKL_0A29WSn1BMn7Jb1X7UB1chVh8kvW4@mail.gmail.com> <OFECB409E6.A28EF58F-ON8625776D.006CCF7C-8625776D.006D9C3B@us.ibm.com> <AANLkTin0MqgK=ttCc2oprD=z2N-7beKoLvM-KhNxDwuB@mail.gmail.com> <AANLkTimYFxc51ZxwiT=rWkF9Do17BGkeEkw3Jf63e=3H@mail.gmail.com> <AANLkTinrNbZXtXiZYhyt0V_ijipZdPR=--KSbE4Ao5yy@mail.gmail.com> <AANLkTi=1c7NCg6Hmhh3BcGZqF9QK7iRkQ8AwMHpssQXi@mail.gmail.com> <AANLkTinwPP8fTrCdFg998ua3Gb-S++9TcenJZb7fWJGy@mail.gmail.com> <AANLkTi=a8ksz1=3dq6f0YYzW7gRqJsEuHbqLwMY8GseO@mail.gmail.com> <AANLkTimX7u+gxcXaqAvah=PJ02jS-7Qk40yjtG9hxMq4@mail.gmail.com> <AANLkTi=X=S-s+DrC7pB0Sm4LAcEXeGn_PruKNLnC3gVZ@mail.gmail.com> <AANLkTinguXaw6KR1xi2Tz3O+wpRxiwAqW28+g+yJC6Lf@mail.gmail.com> <AANLkTinNyB83vfkwZp0Lxu03H+DNpD-AvBt803pt=4qi@mail.gmail.com> <AANLkTikX01vs8_taOwuEnULBkXaRhr1rQHQR4KUMXuM7@mail.gmail.com> <AANLkTiktVKVmNnQRyp=OQfJ1+DAYkRQgTso3Qb-kV3nJ@mail.gmail.com> <AANLkTi=dFqKHoU=xkTuq6bKMvg9f2oGX4UaCot1XS-gP@mail.gmail.com> <AANLkTimEGjvDmFe1qjFvn5gfiNpnnt9ORM6RA6RCXpdY@mail.gmail.com> <AANLkTi=4HF2sKUPfhS5GRJTLW1g7rYRTn8iihkmYH6k2@mail.gmail.com> <AANLkTimk3b3tmDr3g8KKDGvJ6HczpPJXNdGoV9cE0a9A@mail.gmail.com> <AANLkTima5mV3OL=HuY_Sw54NtNU4-0RaY+z6jaNzA0Sc@mail.gmail.com>
Compiler bootstrapped and tested with Lu's patch (with one minor
change to initialize off variable) (x86-64/linux) -- also checked dump
file that offsets are properly computed.
Ok for trunk?
Thanks,
David
On Fri, Jul 30, 2010 at 1:43 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Fri, Jul 30, 2010 at 11:46 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> On Fri, Jul 30, 2010 at 10:54 AM, Xinliang David Li <davidxl@google.com> wrote:
>>> Why is start offset not 1 to begin with? Let's assume it is correct,
>>> there are a couple of problems in this patch:
>>>
>>> 1) when the precision of the HOST_WIDE_INT is the same as the bitsize
>>> of the address_mode, max_offset = (HOST_WIDE_INT) 1 << width will
>>> produce a negative number
>>> 2) last_off should be initialized to 0 to match the original behavior
>>> 3) The i&& guard will make sure the loop terminates, but the offset
>>> compuation will be wrong -- i<<1 will first overflows to a negative
>>> number, then gets truncated to zero, ?that means when this happens,
>>> the last_off will be negative when the loop terminates.
>>>
>>> David
>>
>> I don't know exactly what get_address_cost is supposed to do. Here is
>> a new patch which avoids overflow and speeds up finding max/min offsets.
>>
>
>
> The code is wrong for -m32 on 64bit host. We should start with
> the maximum and minimum offsets like:
>
> ? ? ?width = GET_MODE_BITSIZE (address_mode) - 1;
> ? ? ?if (width > (HOST_BITS_PER_WIDE_INT - 1))
> ? ? ? ?width = HOST_BITS_PER_WIDE_INT - 1;
> ? ? ?addr = gen_rtx_fmt_ee (PLUS, address_mode, reg1, NULL_RTX);
>
> ? ? ?for (i = width; i; i--)
> ? ? ? ?{
> ? ? ? ? ?off = -((HOST_WIDE_INT) 1 << i);
> ? ? ? ? ?XEXP (addr, 1) = gen_int_mode (off, address_mode);
> ? ? ? ? ?if (memory_address_addr_space_p (mem_mode, addr, as))
> ? ? ? ? ? ?break;
> ? ? ? ?}
> ? ? ?data->min_offset = off;
>
> ? ? ?for (i = width; i; i--)
> ? ? ? ?{
> ? ? ? ? ?off = ((HOST_WIDE_INT) 1 << i) - 1;
> ? ? ? ? ?XEXP (addr, 1) = gen_int_mode (off, address_mode);
> ? ? ? ? ?if (memory_address_addr_space_p (mem_mode, addr, as))
> ? ? ? ? ? ?break;
> ? ? ? ?}
> ? ? ?data->max_offset = off;
>
> Here is the updated patch.
>
>
> H.J.
> ---
>> H.J.
>> ---
>>>
>>> On Fri, Jul 30, 2010 at 10:27 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>> On Fri, Jul 30, 2010 at 9:58 AM, Xinliang David Li <davidxl@google.com> wrote:
>>>>> There is a problem in this patch -- when i wraps to zero and terminate
>>>>> the loop, the maxoffset computed will be zero which is wrong.
>>>>>
>>>>> My previous patch won't have this problem.
>>>>
>>>> Your patch changed the start offset. ?Here is the updated patch.
>>>>
>>>>
>>>> H.J.
>>>>>
>>>>> David
>>>>>
>>>>> On Fri, Jul 30, 2010 at 9:49 AM, Xinliang David Li <davidxl@google.com> wrote:
>>>>>> This looks fine to me -- Zdenek or other reviewers --- is this one ok?
>>>>>>
>>>>>> Thanks,
>>>>>>
>>>>>> David
>>>>>>
>>>>>> On Fri, Jul 30, 2010 at 8:45 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>>>>> On Thu, Jul 29, 2010 at 6:04 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>>>>>> It looks strange:
>>>>>>>>
>>>>>>>> + ? ? ?width = (GET_MODE_BITSIZE (address_mode) < ?HOST_BITS_PER_WIDE_INT - 1)
>>>>>>>> + ? ? ? ? ?? GET_MODE_BITSIZE (address_mode) : HOST_BITS_PER_WIDE_INT - 1;
>>>>>>>> ? ? ? addr = gen_rtx_fmt_ee (PLUS, address_mode, reg1, NULL_RTX);
>>>>>>>> - ? ? ?for (i = start; i <= 1 << 20; i <<= 1)
>>>>>>>> + ? ? ?for (i = 1; i < width; i++)
>>>>>>>> ? ? ? ?{
>>>>>>>> - ? ? ? ? XEXP (addr, 1) = gen_int_mode (i, address_mode);
>>>>>>>> + ? ? ? ? ?HOST_WIDE_INT offset = (1ll << i);
>>>>>>>> + ? ? ? ? XEXP (addr, 1) = gen_int_mode (offset, address_mode);
>>>>>>>> ? ? ? ? ?if (!memory_address_addr_space_p (mem_mode, addr, as))
>>>>>>>> ? ? ? ? ? ?break;
>>>>>>>> ? ? ? ?}
>>>>>>>>
>>>>>>>> HOST_WIDE_INT may be long or long long. "1ll" isn't always correct.
>>>>>>>> I think width can be >= 31. Depending on HOST_WIDE_INT,
>>>>>>>>
>>>>>>>> HOST_WIDE_INT offset = -(1ll << i);
>>>>>>>>
>>>>>>>> may have different values. The whole function looks odd to me.
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>> Here is a different approach to check address overflow.
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>> H.J.
>>>>>>> --
>>>>>>> 2010-07-29 ?H.J. Lu ?<hongjiu.lu@intel.com>
>>>>>>>
>>>>>>> ? ? ? ?PR bootstrap/45119
>>>>>>> ? ? ? ?* tree-ssa-loop-ivopts.c (get_address_cost): Re-apply revision
>>>>>>> ? ? ? ?162652. ?Check address overflow.
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> H.J.
>>>>
>>>
>>
>>
>>
>> --
>> H.J.
>>
>
>
>
> --
> H.J.
>
Index: gcc/tree-ssa-loop-ivopts.c
===================================================================
--- gcc/tree-ssa-loop-ivopts.c (revision 162821)
+++ gcc/tree-ssa-loop-ivopts.c (working copy)
@@ -3241,9 +3241,8 @@ get_address_cost (bool symbol_present, b
if (!data)
{
HOST_WIDE_INT i;
- HOST_WIDE_INT start = BIGGEST_ALIGNMENT / BITS_PER_UNIT;
- HOST_WIDE_INT rat, off;
- int old_cse_not_expected;
+ HOST_WIDE_INT rat, off = 0;
+ int old_cse_not_expected, width;
unsigned sym_p, var_p, off_p, rat_p, add_c;
rtx seq, addr, base;
rtx reg0, reg1;
@@ -3252,33 +3251,38 @@ get_address_cost (bool symbol_present, b
reg1 = gen_raw_REG (address_mode, LAST_VIRTUAL_REGISTER + 1);
+ width = GET_MODE_BITSIZE (address_mode) - 1;
+ if (width > (HOST_BITS_PER_WIDE_INT - 1))
+ width = HOST_BITS_PER_WIDE_INT - 1;
addr = gen_rtx_fmt_ee (PLUS, address_mode, reg1, NULL_RTX);
- for (i = start; i <= 1 << 20; i <<= 1)
+
+ for (i = width; i; i--)
{
- XEXP (addr, 1) = gen_int_mode (i, address_mode);
- if (!memory_address_addr_space_p (mem_mode, addr, as))
+ off = -((HOST_WIDE_INT) 1 << i);
+ XEXP (addr, 1) = gen_int_mode (off, address_mode);
+ if (memory_address_addr_space_p (mem_mode, addr, as))
break;
}
- data->max_offset = i == start ? 0 : i >> 1;
- off = data->max_offset;
+ data->min_offset = off;
- for (i = start; i <= 1 << 20; i <<= 1)
+ for (i = width; i; i--)
{
- XEXP (addr, 1) = gen_int_mode (-i, address_mode);
- if (!memory_address_addr_space_p (mem_mode, addr, as))
+ off = ((HOST_WIDE_INT) 1 << i) - 1;
+ XEXP (addr, 1) = gen_int_mode (off, address_mode);
+ if (memory_address_addr_space_p (mem_mode, addr, as))
break;
}
- data->min_offset = i == start ? 0 : -(i >> 1);
+ data->max_offset = off;
if (dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file, "get_address_cost:\n");
- fprintf (dump_file, " min offset %s %d\n",
+ fprintf (dump_file, " min offset %s " HOST_WIDE_INT_PRINT_DEC "\n",
GET_MODE_NAME (mem_mode),
- (int) data->min_offset);
- fprintf (dump_file, " max offset %s %d\n",
+ data->min_offset);
+ fprintf (dump_file, " max offset %s " HOST_WIDE_INT_PRINT_DEC "\n",
GET_MODE_NAME (mem_mode),
- (int) data->max_offset);
+ data->max_offset);
}
rat = 1;