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Ecma edit for conv.ovf.<to type>.un. #56450

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Aug 4, 2021
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Ecma edit for conv.ovf.<to type>.un. #56450

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ec43add
Add a conv conformance test.
Jul 28, 2021
4c33ff7
Fix Ecma description.
Jul 28, 2021
da5491a
Fix the test.
Jul 28, 2021
03cbaca
Update docs/design/specs/Ecma-335-Augments.md
Jul 28, 2021
bc184e9
Disable VN optimizations on arm64 because of the bug.
Jul 29, 2021
8277151
add a new chapter.
Jul 29, 2021
53a92e4
fix space
Jul 30, 2021
b53ff87
Fix format.
Aug 2, 2021
3c28df2
exclude the test on mono
Aug 3, 2021
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29 changes: 28 additions & 1 deletion docs/design/specs/Ecma-335-Augments.md
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Expand Up @@ -11,6 +11,7 @@ This is a list of additions and edits to be made in ECMA-335 specifications. It
- [Default Interface Methods](#default-interface-methods)
- [Static Interface Methods](#static-interface-methods)
- [Covariant Return Types](#covariant-return-types)
- [Unsigned data conversion with overflow detection](#unsigned-data-conversion-with-overflow-detection)

## Signatures

Expand Down Expand Up @@ -907,4 +908,30 @@ For this example, the behavior of calls on objects of various types is presented
| D | B::VirtualFunction() | ERROR | A program containing type D is not valid, as B::VirtualFunction would be implemented by D::VirtualFunction which is not *covariant-return-compatible-with* (§I.8.7.1) B::VirtualFunction |
"
### II.22.27
Edit rule 12 to specify that "The method signature defined by *MethodBody* shall match those defined by *MethodDeclaration* exactly if *MethodDeclaration* defines a method on an interface or be *covariant-return-compatible-with* (§I.8.7.1) if *MethodDeclaration* represents a method on a class."
Edit rule 12 to specify that "The method signature defined by *MethodBody* shall match those defined by *MethodDeclaration* exactly if *MethodDeclaration* defines a method on an interface or be *covariant-return-compatible-with* (§I.8.7.1) if *MethodDeclaration* represents a method on a class."

## Unsigned data conversion with overflow detection

conv.ovf.<to type>.un opcode is purposed for converting a value on the stack to an integral value while treating the stack source as unsigned. Ecma does not distinguish signed and unsigned values on the stack so such opcode is needed as a complement for conv.ovf.<to type>.
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So if the value on the stack is 4-byte size integral created by `Ldc_I4 0xFFFFFFFF` the results of different conversion opcodes will be:
conv.ovf.i4 -> -1 (0xFFFFFFFF)
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conv.ovf.u4 -> overflow
conv.ovf.i4.un -> overflow
conv.ovf.u4.un -> uint.MaxValue (0xFFFFFFFF)

However, the source of these opcodes can be a float value and it was not clear how in such case .un should be treated. The ECMA was saying: ""The item on the top of the stack is treated as an unsigned value before the conversion." but there was no definition of "treated" so the result of:
ldc.r4 -1
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conv.ovf.i4.un
was ambiguous, it could treat -1 as 0xFFFFFFFF and return 0xFFFFFFFF or it could throw an overflow exception.

### III.3.19, conv.ovf.to type.un (page 354)
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This should be put into a new section describing feature area. Effectively, each set of changes to the Ecma standard describes what the general impact is, and then there is the modification to the actual standardese. As it is this work is appended onto the covariant return types work, but really should be in its own chunk.

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I see, I have added a new chapter and tried to add a justification for the change. I have not found a template for this, looks like different chapters are organized differently, please tell me if you want me to add issue numbers, link to the current standard, or something else.

(Edit 1st Description paragraph:)
Convert the value on top of the stack to the type specified in the opcode, and leave that converted
value on the top of the stack. If the value cannot be represented, an exception is thrown.

(Edit 2nd Description paragraph:)

Conversions from floating-point numbers to integral values truncate the number toward zero and used as-is ignoring .un suffix. The integral item
on the top of the stack is reinterpreted as an unsigned value before the conversion.
Note that integer values of less than 4 bytes are extended to int32 (not native int) on the
evaluation stack.
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