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Constant pool should share values #35268

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Constant pool should share values#35268
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JitUntriagedCLR JIT issues needing additional triagearch-x64area-CodeGen-coreclrCLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMIoptimization
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Future

Description

@BruceForstall
BruceForstall
opened on Apr 22, 2020

Doubles added to constant pool are not shared: the same constant appearing multiple times appears multiple times in the constant pool.

Using the example from #35257:

private static double Process(double n)
{
  double res;
  res = 1;
  while (n > 0.0)
  {
    res *= n;
// User might not write such code, but here it is written merely to show that same constants are re-loaded in assembly code.
    n -= 1.0;
    n -= 2.0;
    n -= 1.0;
    n -= 2.0;
  }
  return res;
}

The generated x64 assembly is:

; Assembly listing for method BringUpTest:Process(double):double
; Emitting BLENDED_CODE for X64 CPU with AVX - Windows
; optimized code
; rsp based frame
; fully interruptible
; Final local variable assignments
;
;  V00 arg0         [V00,T00] ( 13, 43   )  double  ->  mm0
;  V01 loc0         [V01,T01] (  4, 10   )  double  ->  mm1
;# V02 OutArgs      [V02    ] (  1,  1   )  lclBlk ( 0) [rsp+0x00]   "OutgoingArgSpace"
;
; Lcl frame size = 0

G_M28499_IG01:
       C5F877               vzeroupper
                                                ;; bbWeight=1    PerfScore 1.00
G_M28499_IG02:
       C5FB100D4D000000     vmovsd   xmm1, qword ptr [reloc @RWD00]
       C5E857D2             vxorps   xmm2, xmm2
       C5F92EC2             vucomisd xmm0, xmm2
       7638                 jbe      SHORT G_M28499_IG04
                                                ;; bbWeight=1    PerfScore 4.33
G_M28499_IG03:
       C5F359C8             vmulsd   xmm1, xmm1, xmm0
       C5FB5C053F000000     vsubsd   xmm0, xmm0, qword ptr [reloc @RWD08]
       C5FB5C053F000000     vsubsd   xmm0, xmm0, qword ptr [reloc @RWD16]
       C5FB5C053F000000     vsubsd   xmm0, xmm0, qword ptr [reloc @RWD24]
       C5FB5C053F000000     vsubsd   xmm0, xmm0, qword ptr [reloc @RWD32]
       C5E857D2             vxorps   xmm2, xmm2
       C5F92EC2             vucomisd xmm0, xmm2
       77D2                 ja       SHORT G_M28499_IG03
                                                ;; bbWeight=4    PerfScore 101.33
G_M28499_IG04:
       C5F828C1             vmovaps  xmm0, xmm1
                                                ;; bbWeight=1    PerfScore 0.25
G_M28499_IG05:
       C3                   ret
                                                ;; bbWeight=1    PerfScore 1.00
RWD00  dq       3FF0000000000000h
RWD08  dq       3FF0000000000000h
RWD16  dq       4000000000000000h
RWD24  dq       3FF0000000000000h
RWD32  dq       4000000000000000h


; Total bytes of code 72, prolog size 3, PerfScore 116.22, (MethodHash=7c9e90ac) for method BringUpTest:Process(double):double
; ============================================================

In this case, RWD00, RWD08, and RWD24 are identical, and RWD16 and RWD32 are identical.

The constant pool is (conceptually) read-only (I believe), so we only need one of each unique value in the table.

category:cq
theme:constant-pool
skill-level:intermediate
cost:medium

Activity

  1. BruceForstall
    added
    arch-x64
    area-CodeGen-coreclrCLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI
    optimization
    on Apr 22, 2020
  2. BruceForstall
    added this to the Future milestone on Apr 22, 2020
  3. Dotnet-GitSync-Bot
    added
    untriagedNew issue has not been triaged by the area owner
    on Apr 22, 2020
  4. BruceForstall
    removed
    untriagedNew issue has not been triaged by the area owner
    on Apr 24, 2020
  5. BruceForstall
    added
    JitUntriagedCLR JIT issues needing additional triage
    on Oct 28, 2020

  6. anthonycanino commented on Nov 1, 2021

    @anthonycanino
    anthonycanino
    on Nov 1, 2021
    Contributor

    @BruceForstall

    I think this issue may have been resolved. On my machine, the sample above generates the following code:

    ; Assembly listing for method Program:Process(double):double
; Emitting BLENDED_CODE for X64 CPU with AVX - Windows
; optimized code
; rsp based frame
; fully interruptible
; No PGO data
; Final local variable assignments
;
;  V00 arg0         [V00,T00] ( 13, 43   )  double  ->  mm0        
;  V01 loc0         [V01,T01] (  4, 10   )  double  ->  mm1        
;# V02 OutArgs      [V02    ] (  1,  1   )  lclBlk ( 0) [rsp+00H]   "OutgoingArgSpace"
;  V03 cse0         [V03,T02] (  3,  9   )  double  ->  mm2         "CSE - aggressive"
;
; Lcl frame size = 0

G_M22436_IG01:              ;; offset=0000H
       C5F877               vzeroupper 
						;; bbWeight=1    PerfScore 1.00
G_M22436_IG02:              ;; offset=0003H
       C5FB100D4D000000     vmovsd   xmm1, qword ptr [reloc @RWD00]
       C5E857D2             vxorps   xmm2, xmm2
       C5F92EC2             vucomisd xmm0, xmm2
       7636                 jbe      SHORT G_M22436_IG04
       C5FB101543000000     vmovsd   xmm2, qword ptr [reloc @RWD08]
                            align    [0 bytes]
						;; bbWeight=1    PerfScore 9.33
G_M22436_IG03:              ;; offset=001DH
       C5F359C8             vmulsd   xmm1, xmm1, xmm0
       C5FB5C052F000000     vsubsd   xmm0, xmm0, qword ptr [reloc @RWD00]
       C5FB5CC2             vsubsd   xmm0, xmm0, xmm2
       C5FB5C0523000000     vsubsd   xmm0, xmm0, qword ptr [reloc @RWD00]
       C5FB5CC2             vsubsd   xmm0, xmm0, xmm2
       C5E057DB             vxorps   xmm3, xmm3
       C5F92EC3             vucomisd xmm0, xmm3
       77DA                 ja       SHORT G_M22436_IG03
						;; bbWeight=4    PerfScore 89.33
G_M22436_IG04:              ;; offset=0043H
       C5F828C1             vmovaps  xmm0, xmm1
						;; bbWeight=1    PerfScore 0.25
G_M22436_IG05:              ;; offset=0047H
       C3                   ret      
						;; bbWeight=1    PerfScore 1.00
RWD00  	dq	3FF0000000000000h	;            1
RWD08  	dq	4000000000000000h	;            2

    Looks like only two constants are created in the constant pool now. Perhaps this was solved with: #44419

  7. BruceForstall commented on Nov 1, 2021

    @BruceForstall
    BruceForstall
    on Nov 1, 2021
    ContributorAuthor

    Thanks for checking. I'll go ahead and close this issue.

  8. BruceForstall
    closed this as completedon Nov 1, 2021
  9. ghost locked as resolved and limited conversation to collaborators on Dec 2, 2021
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