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Incorrect codegen for Vector256.Create(0, 0, 0, 0, 1, 1, 1, 1) #47236

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#47385
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Incorrect codegen for Vector256.Create(0, 0, 0, 0, 1, 1, 1, 1)#47236
#47385
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EgorBo
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area-CodeGen-coreclrCLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMIbug
Milestone
6.0.0

Description

@Sergio0694
Sergio0694
opened on Jan 20, 2021

Description

Stumbled upon this issue while working on SixLabors/ImageSharp#1513.
Looks like that Vector256.Create(0, 0, 0, 0, 1, 1, 1, 1) results in just a vxorps, so it effectively just zeroes the register.
You can repro this by just creating a value into a local and calling ToString() on it: all values are just 0.

Configuration

  • .NET 5.0.101
  • Checked with both sharplab, and locally with disasmo on a recent CoreCLR build

Regression?

Yes, it seems to work fine on .NET Core 3.1.

Codegen (disasmo)

public static void Foo(ref Vector256<int> x)
{
    x = Vector256.Create(0, 0, 0, 0, 1, 1, 1, 1);
}
; Assembly listing for method Vector256CreateRepro.Program:Foo(byref)
; Emitting BLENDED_CODE for X64 CPU with AVX - Windows
; optimized code
; rsp based frame
; partially interruptible
; Final local variable assignments
;
;  V00 arg0         [V00,T00] (  3,  3   )   byref  ->  rcx        
;# V01 OutArgs      [V01    ] (  1,  1   )  lclBlk ( 0) [rsp+0x00]   "OutgoingArgSpace"
;
; Lcl frame size = 0

G_M21017_IG01:
       vzeroupper 
						;; bbWeight=1    PerfScore 1.00
G_M21017_IG02:
       vxorps   ymm0, ymm0, ymm0
       vmovupd  ymmword ptr[rcx], ymm0
						;; bbWeight=1    PerfScore 3.33
G_M21017_IG03:
       vzeroupper 
       ret      
						;; bbWeight=1    PerfScore 2.00

; Total bytes of code 15, prolog size 3, PerfScore 8.03, instruction count 5 (MethodHash=f2a3ade6) for method Vector256CreateRepro.Program:Foo(byref)
; ============================================================

Activity

  1. ghost added
    area-CodeGen-coreclrCLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI
    on Jan 20, 2021
  2. ghost added
    untriagedNew issue has not been triaged by the area owner
    on Jan 20, 2021

  3. tannergooding commented on Jan 20, 2021

    @tannergooding
    tannergooding
    on Jan 20, 2021
    Member

    I was able to repro, however, this no longer repros if you change any of the values in the Create constant.

  4. Sergio0694
    added a commit that references this issue on Jan 20, 2021

    Workaround for incorrect codegen on .NET 5

    a7ca1b0

  5. Sergio0694 commented on Jan 20, 2021

    @Sergio0694
    Sergio0694
    on Jan 20, 2021
    ContributorAuthor

    Yeah it seems like this only happens with exactly (0, 0, 0, 0, 1, 1, 1, 1) as arguments 🤔

  6. EgorBo commented on Jan 20, 2021

    @EgorBo
    EgorBo
    on Jan 20, 2021
    Member

    Bug-fix: EgorBo@1809af6

    The bug should also reproduce for e.g. (0, 0, 0, 0, 5, 5, 5, 5)

  7. JulieLeeMSFT commented on Jan 20, 2021

    @JulieLeeMSFT
    JulieLeeMSFT
    on Jan 20, 2021
    Member

    @EgorBo I will assign this to you.

  8. JulieLeeMSFT
    removed
    untriagedNew issue has not been triaged by the area owner
    on Jan 20, 2021
  9. JulieLeeMSFT
    assigned
    EgorBo
    on Jan 20, 2021
  10. JulieLeeMSFT
    added this to the 6.0.0 milestone on Jan 20, 2021
  11. JulieLeeMSFT
    added
    bug
    on Jan 20, 2021
  12. ghost added
    in-prThere is an active PR which will close this issue when it is merged
    on Jan 24, 2021
  13. EgorBo
    closed this as completedin #47385on Feb 16, 2021
  14. ghost removed
    in-prThere is an active PR which will close this issue when it is merged
    on Feb 16, 2021
  15. JimBobSquarePants
    added a commit that references this issue on Mar 13, 2021

    Workaround for incorrect codegen on .NET 5

    ed4cfaa
  16. ghost locked as resolved and limited conversation to collaborators on Mar 18, 2021
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