Re: [Patch] Add MIPS flag to avoid use of ldc1/sdc1/ldxc1/sdxc1

[Andrew Pinski <pinskia at gmail dot com>]

On Mon, Oct 27, 2014 at 3:35 PM, Moore, Catherine
<Catherine_Moore@mentor.com> wrote:
>
>
>> -----Original Message-----
>> From: Andrew Pinski [mailto:pinskia@gmail.com]
>> Sent: Monday, October 27, 2014 6:32 PM
>> To: Steve Ellcey
>> Cc: Moore, Catherine; Matthew Fortune; GCC Patches
>> Subject: Re: [Patch] Add MIPS flag to avoid use of ldc1/sdc1/ldxc1/sdxc1
>>
>> On Mon, Oct 27, 2014 at 3:23 PM, Steve Ellcey <sellcey@imgtec.com> wrote:
>> >
>> > There are some MIPS patches that have been applied to the Google
>> > Android GCC tree but not been submitted to FSF GCC.  I would like to get
>> those patches
>> > checked in if possible.   The first one is to add a new MIPS flag to turn
>> > off the use of ldc1/sdc1/ldxc1/sdxc1.  Google Earth has a custom
>> > allocator that does not guarantee 8 byte alignment of the allocated
>> > memory, therefore using these instructions (that require 8 byte
>> > alignment) could cause runtime failures.  By default, these
>> > instructions will continue to be used, the flag is there to allow their use to
>> be turned off if desired.
>>
>> That sounds like a bug in google earth's allocator if we follow either C or C++
>> standards when it comes to malloc/operator new.
>> Both have to be align enough for the type which is at least that size that is
>> being allocated.  So it needs to be 8byte aligned if allocating a 8 byte object.
>>
>
>   Andrew,
>
>   Do you have an objection to allowing an option to disable these instructions (despite the reason for wanting to do so)?

Yes this seems like a bad workaround for broken code.

Thanks,
Andrew Pinski


>
>   Thanks,
>   Catherine
>
>>
>> >
>> > Tested on mips-mti-linux-gnu.
>> >
>> > OK to checkin?
>> >
>> > Steve Ellcey
>> > sellcey@imgtec.com
>> >
>> >
>> >
>> > 2014-10-27  Steve Ellcey  <sellcey@imgtec.com>
>> >
>> >         * config/mips/mips.h (ISA_HAS_LDC1_SDC1): Check
>> TARGET_LDC1_SDC1.
>> >         * config/mips/mips.md (*<ANYF:loadx>_<P:mode): Ditto.
>> >         * config/mips/mips.md (*<ANYF:storex>_<P:mode): Ditto.
>> >         * config/mips/mips.opt (mldc1-sdc1): New.
>> >
>> >
>> > diff --git a/gcc/config/mips/mips.h b/gcc/config/mips/mips.h index
>> > c7b998b..b9caff7 100644
>> > --- a/gcc/config/mips/mips.h
>> > +++ b/gcc/config/mips/mips.h
>> > @@ -892,7 +892,8 @@ struct mips_cpu_info {
>> >  /* ISA has LDC1 and SDC1.  */
>> >  #define ISA_HAS_LDC1_SDC1      (!ISA_MIPS1                             \
>> >                                  && !TARGET_MIPS5900                    \
>> > -                                && !TARGET_MIPS16)
>> > +                                && !TARGET_MIPS16                      \
>> > +                                && TARGET_LDC1_SDC1)
>> >
>> >  /* ISA has the mips4 FP condition code instructions: FP-compare to CC,
>> >     branch on CC, and move (both FP and non-FP) on CC.  */ diff --git
>> > a/gcc/config/mips/mips.md b/gcc/config/mips/mips.md index
>> > d47bb78..77f3356 100644
>> > --- a/gcc/config/mips/mips.md
>> > +++ b/gcc/config/mips/mips.md
>> > @@ -4573,7 +4573,7 @@
>> >    [(set (match_operand:ANYF 0 "register_operand" "=f")
>> >         (mem:ANYF (plus:P (match_operand:P 1 "register_operand" "d")
>> >                           (match_operand:P 2 "register_operand"
>> > "d"))))]
>> > -  "ISA_HAS_LXC1_SXC1"
>> > +  "ISA_HAS_LXC1_SXC1 && (<MODE>mode == SFmode ||
>> TARGET_LDC1_SDC1)"
>> >    "<ANYF:loadx>\t%0,%1(%2)"
>> >    [(set_attr "type" "fpidxload")
>> >     (set_attr "mode" "<ANYF:UNITMODE>")]) @@ -4582,7 +4582,7 @@
>> >    [(set (mem:ANYF (plus:P (match_operand:P 1 "register_operand" "d")
>> >                           (match_operand:P 2 "register_operand" "d")))
>> >         (match_operand:ANYF 0 "register_operand" "f"))]
>> > -  "ISA_HAS_LXC1_SXC1"
>> > +  "ISA_HAS_LXC1_SXC1 && (<MODE>mode == SFmode ||
>> TARGET_LDC1_SDC1)"
>> >    "<ANYF:storex>\t%0,%1(%2)"
>> >    [(set_attr "type" "fpidxstore")
>> >     (set_attr "mode" "<ANYF:UNITMODE>")]) diff --git
>> > a/gcc/config/mips/mips.opt b/gcc/config/mips/mips.opt index
>> > dca4f80..7b75fc9 100644
>> > --- a/gcc/config/mips/mips.opt
>> > +++ b/gcc/config/mips/mips.opt
>> > @@ -267,6 +267,10 @@ mips3d
>> >  Target Report RejectNegative Var(TARGET_MIPS3D)  Use MIPS-3D
>> > instructions
>> >
>> > +mldc1-sdc1
>> > +Target Report Var(TARGET_LDC1_SDC1) Init(1) Use ldc1/ldxc1 and
>> > +sdc1/sdxc1 instruction
>> > +
>> >  mllsc
>> >  Target Report Mask(LLSC)
>> >  Use ll, sc and sync instructions