X86 Debug Stack offsets are encoded divided by 4

[davidwrighton]

• Fix the encoding

Fixes #57951

[AndyAyersMS]

Seems like that should do the trick.

Can you verify the new R2R debug info for x86 Task.WaitAll looks right?

[trylek]

LGTM, thanks David for fixing this so quickly!

[trylek]

Nit - if at some point we considered expanding this behavior to other architectures, the name of the argument (assume4ByteAligned) would probably need to change to e.g. something like encodeUsingPointerSizeUnits or some such. If we believe this to be limited to X86 forever, it's probably OK.

[davidwrighton]

I just checked to see how valuable this really is, and we could save something like 0.08% of System.Private.CoreLib.dll size if we applied a similar size optimization on X64. I don't see that as worthwhile given the complexity it would impose on the reader in the runtime.

[davidwrighton]

@AndyAyersMS Yep. Verified the WaitAll behavior, and it looks good.

void System.Threading.Tasks.Task.WaitAll(System.Threading.Tasks.Task[])
Handle: 0x060032D8
Rid: 13016
EntryPointRuntimeFunctionId: 10598
Number of RuntimeFunctions: 1
Number of fixups: 1
    TableIndex 4, Offset 0380: System.Threading.CancellationToken (TYPE_HANDLE)

void System.Threading.Tasks.Task.WaitAll(System.Threading.Tasks.Task[])
Id: 10598
StartAddress: 0x002743C0
Size: 40 bytes
UnwindRVA: 0x000425B0

Debug Info
    Bounds:
    Native Offset: 0x0, Prolog, Source Types: StackEmpty
    Native Offset: 0xE, IL Offset: 0x0000, Source Types: StackEmpty
    Native Offset: 0x24, IL Offset: 0x0011, Source Types: StackEmpty
    Native Offset: 0x24, Epilog, Source Types: StackEmpty

    Variable Locations:
    Variable Number: 0
    Start Offset: 0x0
    End Offset: 0xE
    Loc Type: VLT_REG
    Register: ECX

    Variable Number: 0
    Start Offset: 0xE
    End Offset: 0x24
    Loc Type: VLT_STK
    Base Register: EBP
    Stack Offset: -4

    Variable Number: 1
    Start Offset: 0xE
    End Offset: 0x24
    Loc Type: VLT_STK
    Base Register: EBP
    Stack Offset: -8

[davidwrighton]

/backport to release/6.0-rc1

[github-actions]

Started backporting to release/6.0-rc1: https://github.com/dotnet/runtime/actions/runs/1165066676

[MichalStrehovsky]

TargetDetails are available in _method.Context.Target. The additional parameter caused an unnecessary NativeAOT build break.