JIT: Allow forward substituting small-typed nodes

[jakobbotsch]

#79408 (comment)

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Issue Details

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Author:	jakobbotsch
Assignees:	jakobbotsch
Labels:	area-CodeGen-coreclr
Milestone:	-

[jakobbotsch]

/azp run Fuzzlyn

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[jakobbotsch]

Fuzzlyn failure looks unrelated, will open a separate issue for that.

Going to bounce this... looks like it got caught up in the GitHub outage, the CI runs are actually finished but the check statuses haven't updated.

[jakobbotsch]

/azp run runtime-coreclr jitstress, runtime-coreclr libraries-jitstress

[azure-pipelines]

Azure Pipelines successfully started running 2 pipeline(s).

[jakobbotsch]

The failure is #80857.

Diffs. Some of the regressions are due to some casts we no longer omit without local copy prop, before:

fgMorphTree BB01, STMT00004 (before)
               [000016] -A---------                         ▌  ASG       bool  
               [000015] D------N---                         ├──▌  LCL_VAR   bool   V04 tmp2         
               [000014] -----------                         └──▌  LCL_VAR   int    V03 tmp1          (last use)
GenTreeNode creates assertion:
               [000016] -A---+-----                         ▌  ASG       bool  
In BB01 New Local Copy     Assertion: V04 == V03, index = #03

fgMorphTree BB01, STMT00003 (before)
               [000010] -----------                         ▌  RETURN    struct
               [000009] -----------                         └──▌  LCL_VAR   struct<System.Text.Json.Nodes.JsonNodeOptions, 1>(P) V01 loc0         
                                                            └──▌    bool   V01.<unknown class>:<PropertyNameCaseInsensitive>k__BackingField (offs=0x00) -> V04 tmp2          (last use)
Replacing an independently promoted local var V01 with its only field  V04 for the return [000009]

Assertion prop in BB01:
Copy     Assertion: V04 == V03, index = #03
               [000009] -----------                         ▌  LCL_VAR   bool   V03 tmp1         

fgMorphTree BB01, STMT00003 (after)
               [000010] -----+-----                         ▌  RETURN    struct
               [000009] -----+-----                         └──▌  LCL_VAR   bool   V03 tmp1         

After:

fgMorphTree BB01, STMT00004 (after)
               [000016] -A-XG+-----                         ▌  ASG       bool  
               [000015] D----+-N---                         ├──▌  LCL_VAR   bool   V04 tmp2         
               [000011] ---XG+-----                         └──▌  IND       bool  
               [000021] -----+-----                            └──▌  ADD       byref 
               [000005] -----+-----                               ├──▌  LCL_VAR   ref    V00 this          (last use)
               [000020] -----+-----                               └──▌  CNS_INT   long   134 Fseq[<unknown field>]

fgMorphTree BB01, STMT00003 (before)
               [000010] -----------                         ▌  RETURN    struct
               [000009] -----------                         └──▌  LCL_VAR   struct<System.Text.Json.Nodes.JsonNodeOptions, 1>(P) V01 loc0         
                                                            └──▌    bool   V01.<unknown class>:<PropertyNameCaseInsensitive>k__BackingField (offs=0x00) -> V04 tmp2          (last use)
Replacing an independently promoted local var V01 with its only field  V04 for the return [000009]

fgMorphTree BB01, STMT00003 (after)
               [000010] -----+-----                         ▌  RETURN    struct
               [000022] -----+-----                         └──▌  CAST      int <- bool <- int
               [000009] -----+-----                            └──▌  LCL_VAR   int    V04 tmp2          (last use)

cc @dotnet/jit-contrib PTAL @AndyAyersMS