[PATCH] D84324: AMDGPU/GlobalISel: Lower G_FREM

Thu Jul 23 07:35:09 PDT 2020

arsenm added a comment.

In D84324#2169348 <https://reviews.llvm.org/D84324#2169348>, @foad wrote:

> In D84324#2169293 <https://reviews.llvm.org/D84324#2169293>, @arsenm wrote:
>
> > In D84324#2169289 <https://reviews.llvm.org/D84324#2169289>, @foad wrote:
> >
> > > > I'd still like to understand why this is failing conformance if I use frem for opencl fmod.
> > >
> > > What is the alternative to using frem, that passes conformance?
> >
> >
> > A huge expansion that involves loops:
> >  https://github.com/RadeonOpenCompute/ROCm-Device-Libs/blob/amd-stg-open/ocml/src/remainderF_base.h#L38
>
>
> Then it needs debugging. Perhaps there are cases where the simple expansion gives fmod(x,y)==y, even though the result is supposed to have magnitude strictly less than y. Or perhaps it doesn't handle nans or infinities correctly.

The errors aren't small, and aren't just edge cases:
ERROR: fmod: inf ulp error at {-0x1.7a1ba8p+111 (0xf73d0dd4), -0x1.5b9526p-97 (0x8f2dca93)}: *-0x1.c5f348p-98 vs. inf (0x7f800000) at index: 3

ERROR: fmod: -inf ulp error at {0x1.80bb0ep+70 (0x62c05d87), 0x1.08e51ap-82 (0x1684728d)}: *0x1.9d1d8cp-83 vs. -inf (0xff800000) at index: 0

ERROR: fmod: -134961856.000000 ulp error at {-0x1.f47464p-69 (0x9d7a3a32), -0x1.9bdef4p-97 (0x8f4def7a)}: *-0x1.682a78p-98 vs. -0x1.17eep-94 (0x908bf700) at index: 0

ERROR: fmod: inf ulp error at {-0x1.50c0b6p+67 (0xe128605b), 0x1.80b7ep-90 (0x12c05bf0)}: *-0x1.fa594p-91 vs. inf (0x7f800000) at index: 3

ERROR: fmod: -672311475662299076755456.000000 ulp error at {0x1.f8807ep+111 (0x777c403f), -0x1.7711aap+32 (0xcfbb88d5)}: *0x1.b2ab38p+30 vs. -0x1.1cbc28p+86 (0xea8e5e14) at index: 1

ERROR: fmod: 20258841443692227182914624580021649408.000000 ulp error at {-0x1.0107a4p+41 (0xd40083d2), -0x1.144c6ap-86 (0x948a2635)}: *-0x1.85d4acp-87 vs. 0x1.e7b6cp+13 (0x4673db60) at index: 2

ERROR: fmod: -29506071830531670016.000000 ulp error at {0x1.804b2cp+9 (0x44402596), -0x1.477f18p-57 (0xa323bf8c)}: *0x1.41dc88p-57 vs. -0x1.997aap-16 (0xb7ccbd50) at index: 4

ERROR: fmod: 211623838063271919251058575015936.000000 ulp error at {0x1.4d90a4p+41 (0x5426c852), 0x1.96784ap-65 (0x1f4b3c25)}: *0x1.61a4fp-68 vs. 0x1.4de23p+16 (0x47a6f118) at index: 3

ERROR: fmod: -inf ulp error at {0x1.9aedb8p+83 (0x694d76dc), 0x1.4c23f2p-119 (0x42611f9)}: *0x1.bba984p-120 vs. -inf (0xff800000) at index: 0

ERROR: fmod: 100959080964579999364158242467109404672.000000 ulp error at {0x1.aa412p+26 (0x4cd52090), -0x1.92be06p-101 (0x8d495f03)}: *0x1.59267p-101 vs. 0x1.2fd00cp+2 (0x4097e806) at index: 0

ERROR: fmod: inf ulp error at {-0x1.6ebdap+99 (0xf1375ed0), -0x1.fe72bp-36 (0xadff3958)}: *-0x1.39174p-38 vs. inf (0x7f800000) at index: 0

ERROR: fmod: -101767765295104.000000 ulp error at {-0x1.7f0c94p+21 (0xca3f864a), 0x1.8df2eap-29 (0x3146f975)}: *-0x1.191792p-29 vs. -0x1.723aap-6 (0xbcb91d50) at index: 4

ERROR: fmod: 5685162310369280.000000 ulp error at {-0x1.8ccd58p-14 (0xb8c666ac), 0x1.b15ed6p-71 (0x1c58af6b)}: *-0x1.b6d34p-74 vs. 0x1.432ap-45 (0x29219500) at index: 2

ERROR: fmod: inf ulp error at {-0x1.5e45dep+81 (0xe82f22ef), -0x1.4bae4cp-112 (0x87a5d726)}: *-0x1.56f99p-114 vs. inf (0x7f800000) at index: 1

ERROR: fmod: -inf ulp error at {0x1.cd2da6p+126 (0x7ee696d3), -0x1.647a26p-40 (0xabb23d13)}: *0x1.03ad2ap-40 vs. -inf (0xff800000) at index: 3

ERROR: fmod: -50753958115442425856.000000 ulp error at {-0x1.abb154p+118 (0xfad5d8aa), 0x1.8eb61ap+61 (0x5e475b0d)}: *-0x1.eeecp+52 vs. -0x1.602d24p+94 (0xeeb01692) at index: 0

ERROR: fmod: 65524330144892614344704.000000 ulp error at {0x1.ce604ap+11 (0x45673025), 0x1.0bbbaap-65 (0x1f05ddd5)}: *0x1.e25edp-66 vs. 0x1.bc0298p-14 (0x38de014c) at index: 1

ERROR: fmod: -inf ulp error at {0x1.c98fd6p+122 (0x7ce4c7eb), 0x1.fe4a44p-116 (0x5ff2522)}: *0x1.98780cp-116 vs. -inf (0xff800000) at index: 0

ERROR: fmod: inf ulp error at {-0x1.3132dep+84 (0xe998996f), -0x1.a91dcep-110 (0x88d48ee7)}: *-0x1.9270eap-110 vs. inf (0x7f800000) at index: 4

ERROR: fmod: -inf ulp error at {0x1.24c0e6p+36 (0x51926073), -0x1.a5528ap-122 (0x82d2a945)}: *0x1.86bd68p-122 vs. -inf (0xff800000) at index: 1

ERROR: fmod: 328137422309548672426878384939712118784.000000 ulp error at {-0x1.f16f6cp+68 (0xe1f8b7b6), 0x1.34d296p-58 (0x229a694b)}: *-0x1.5fa6ap-61 vs. 0x1.edb9fp+43 (0x5576dcf8) at index: 2

ERROR: fmod: -355087763374080.000000 ulp error at {0x1.b2ab98p+95 (0x6f5955cc), -0x1.ffc7fcp+45 (0xd67fe3fe)}: *0x1.fe7558p+45 vs. -0x1.42f35p+70 (0xe2a179a8) at index: 7

ERROR: fmod: -22169001879878959779282944.000000 ulp error at {-0x1.92d1bap-15 (0xb84968dd), -0x1.a4b14cp-100 (0x8dd258a6)}: *-0x1.38fb4p-103 vs. -0x1.25678p-42 (0xaa92b3c0) at index: 1

ERROR: fmod: inf ulp error at {-0x1.080adep+92 (0xed84056f), -0x1.c2f17cp-77 (0x996178be)}: *-0x1.cd9d5p-79 vs. inf (0x7f800000) at index: 0

ERROR: fmod: inf ulp error at {-0x1.17f76ap+95 (0xef0bfbb5), -0x1.4e0fe4p-108 (0x89a707f2)}: *-0x1.a2f8c8p-109 vs. inf (0x7f800000) at index: 2

ERROR: fmod: -6874084436590301837445300224.000000 ulp error at {0x1.697b38p+54 (0x5ab4bd9c), 0x1.f3988cp-39 (0x2c79cc46)}: *0x1.b4c1ap-40 vs. -0x1.6361cp+29 (0xce31b0e0) at index: 1

ERROR: fmod: -8738995383377592320.000000 ulp error at {0x1.496b64p+85 (0x6a24b5b2), 0x1.bae466p+24 (0x4bdd7233)}: *0x1.7a58cp+20 vs. -0x1.e51c98p+59 (0xdd728e4c) at index: 1

ERROR: fmod: 343065079314668060672.000000 ulp error at {-0x1.21b74ap-47 (0xa810dba5), 0x1.fdb82ep-117 (0x57edc17)}: *-0x1.606e5ap-117 vs. 0x1.298fcp-72 (0x1b94c7e0) at index: 4

ERROR: fmod: -inf ulp error at {0x1.8cdda2p+60 (0x5dc66ed1), 0x1.aeea96p-109 (0x957754b)}: *0x1.6ac0ep-112 vs. -inf (0xff800000) at index: 2

ERROR: fmod: -2991471016484578263040000.000000 ulp error at {-0x1.6a71bep+46 (0xd6b538df), -0x1.4091d2p-34 (0xaea048e9)}: *-0x1.7398e8p-36 vs. -0x1.3cbbfcp+22 (0xca9e5dfe) at index: 3

ERROR: fmod: -inf ulp error at {0x1.ec3bf8p+71 (0x63761dfc), -0x1.36870ep-68 (0x9d9b4387)}: *0x1.06b884p-68 vs. -inf (0xff800000) at index: 0

ERROR: fmod: -1561864113370783809536.000000 ulp error at {0x1.c99b3ap+127 (0x7f64cd9d), -0x1.8f9088p+58 (0xdcc7c844)}: *0x1.aed24p+55 vs. -0x1.52acep+102 (0xf2a95670) at index: 0

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https://reviews.llvm.org/D84324