Type memory maps with placeholders

[SingleAccretion]

Use TYP_UNDEF (as TYP_MEM) for "first field"-like maps and TYP_UNKNOWN (as TYP_HEAP) for the heaps themselves.

This will enable the type validation logic to be more precise. For now though, just assert that the heap is always updated with the properly typed VNs.

Sample from the new dump showcasing the now-more-apparent hierarchy of maps:

***** BB01, STMT00000(before)
N006 (  6,  6) [000010] -A-XG-------              *  ASG       long  
N004 (  4,  4) [000009] *--XG--N----              +--*  IND       long  
N003 (  2,  2) [000016] -------N----              |  \--*  ADD       byref 
N001 (  1,  1) [000000] ------------              |     +--*  LCL_VAR   ref    V00 arg0         u:1 (last use)
N002 (  1,  1) [000015] ------------              |     \--*  CNS_INT   long   56 field offset Fseq[LargeStruct, SmallerStruct1, MultiRegStruct2, FirstLngValue]
N005 (  1,  1) [000008] ------------              \--*  CNS_INT   long   2

N001 [000000]   LCL_VAR   V00 arg0         u:1 (last use) => $80 {InitVal($40)}
N002 [000015]   CNS_INT   56 field offset Fseq[LargeStruct, SmallerStruct1, MultiRegStruct2, FirstLngValue] => $100 {LngCns:  56}
N003 [000016]   ADD       => $140 {ADD($80, $100)}
N005 [000008]   CNS_INT   2 => $101 {LngCns:  2}
    VNForHandle(LargeStruct) is $180, fieldType is struct, size = 96
    VNForMapSelect($c0, $180):mem returns $1c0 {$c0[$180]}
    VNForMapSelect($1c0, $80):struct returns $200 {$1c0[$80]}
    VNForHandle(SmallerStruct1) is $181, fieldType is struct, size = 48
    VNForMapSelect($200, $181):struct returns $201 {$200[$181]}
    VNForHandle(MultiRegStruct2) is $182, fieldType is struct, size = 16
    VNForMapSelect($201, $182):struct returns $202 {$201[$182]}
  VNApplySelectorsAssign:
    VNForHandle(FirstLngValue) is $183, fieldType is long
    VNForMapStore($202, $183, $101):struct in BB01 returns $240 {$202[$183 := $101]}
    VNForMapStore($201, $182, $240):struct in BB01 returns $241 {$201[$182 := $240]}
    VNForMapStore($200, $181, $241):struct in BB01 returns $242 {$200[$181 := $241]}
    VNForMapStore($1c0, $80, $242):mem in BB01 returns $280 {$1c0[$80 := $242]}
    VNForMapStore($c0, $180, $280):heap in BB01 returns $2c0 {$c0[$180 := $280]}
  fgCurMemoryVN[GcHeap] assigned for StoreField at [000010] to VN: $2c0.
N006 [000010]   ASG       => $VN.Void

No diffs.

Part of #58312.

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Issue Details

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Use TYP_UNDEF (as TYP_MEM) for "first field"-like maps and TYP_UNKNOWN (as TYP_HEAP) for the heaps themselves.

This will enable the type validation logic to be more precise. For now though, just assert that the heap is always updated with the properly typed VNs.

No diffs are expected...

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

[SingleAccretion]

@dotnet/jit-contrib

[jakobbotsch]

Looks good.