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Add return value variable homes #128397

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10 changes: 8 additions & 2 deletions docs/design/datacontracts/DebugInfo.md
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Original file line number Diff line number Diff line change
Expand Up @@ -335,6 +335,7 @@
public uint StartOffset { get; init; }
public uint EndOffset { get; init; }
public uint VarNumber { get; init; }
public uint ReturnValueILOffset { get; init; }
public DebugVarLocKind Kind { get; init; }
public bool IsByRef { get; init; }
public uint Register { get; init; }
Expand All @@ -352,7 +353,8 @@
Additional constants (Version 2):
| Constant Name | Meaning | Value |
| --- | --- | --- |
| `MAX_ILNUM` | Bias for adjusted encoding of variable numbers | `0xfffffffc` (-4) |
| `MAX_ILNUM` | Bias for adjusted encoding of variable numbers | `0xfffffffb` (-5) |
| `CALL_RETURN_ILNUM` | A sentinel variable number indicating this variable home stores a call return value | `0xfffffffb` (-5) |
Comment on lines +356 to +357
| `VLT_REG` | Variable is in a register | `0` |
| `VLT_REG_BYREF` | Address of the variable is in a register | `1` |
| `VLT_REG_FP` | Variable is in an FP register | `2` |
Expand All @@ -372,7 +374,11 @@
Each variable entry in the Vars section is nibble-encoded as follows:

1. `startOffset` — encoded unsigned 32-bit integer
2. `endOffset` — encoded as delta from `startOffset` (unsigned)
2. `endOffset` or `returnValueILOffset` depending on the following `varNumber`

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MD009/no-trailing-spaces Trailing spaces [Expected: 0 or 2; Actual: 1]

If varNumber == CALL_RETURN_ILNUM: `returnValueILOffset` encoded as unsigned 32-bit integer. `EndOffset` is implicitly `StartOffset+1`. `ReturnValueILOffset` identifies the offset of the IL call instruction whose return value is stored in this home.
If varNumber != CALL_RETURN_ILNUM: `endOffset` encoded as delta from `startOffset` (unsigned). `ReturnValueILOffset` is implicitly zero though it is unused and meaningless in this case.

3. `varNumber` — encoded as adjusted unsigned (`value - MAX_ILNUM`)
Comment on lines 374 to 382
4. `VarLocType` — encoded unsigned 32-bit integer
5. Location fields depend on the `VarLocType`:
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