Closed
Description
Description
Given:
struct Example
{
object? Value;
ulong Inner;
struct ExampleInner { int Offset; int Length }
public int Offset
{
get
{
var inner = Inner;
return Unsafe.As<ulong, ExampleInner>(ref inner).Offset;
}
}
public int Length
{
get
{
var inner = Inner;
return Unsafe.As<ulong, ExampleInner>(ref inner).Length;
}
}
}It appears that accessing ExampleInner fields stored as ulong produces invalid codegen on FullOpts but not on MinOpts or with Unsafe.BitCast: the produced assembly reads the Length field at the offset of 8 bytes instead of 12.
Reproduction Steps
- Create new console application
- Paste https://gist.github.com/neon-sunset/fed48339292c0cc1f153bf30ffb1ebca into
Program.cs dotnet run -c release
Expected behavior
Output:
--- MinOpts
Offset: 1234
Length: 5678
--- As
Offset: 1234
Length: 5678
--- Bitcast
Offset: 1234
Length: 5678
Actual behavior
Output:
--- MinOpts
Offset: 1234
Length: 5678
--- As
Offset: 1234
Length: 1234 <--- Unexpected
--- Bitcast
Offset: 1234
Length: 5678
Regression?
Yes, does not reproduce on .NET 7 and .NET 6.
Known Workarounds
None, bitcast produces worse codegen.
Configuration
Reproduced on:
.NET SDK:
Version: 8.0.100-preview.7.23364.31
Commit: 378e8abf4f
Runtime Environment:
OS Name: Mac OS X
OS Version: 14.0
OS Platform: Darwin
RID: osx-arm64
Base Path: /usr/local/share/dotnet/sdk/8.0.100-preview.7.23364.31/
.NET SDK:
Version: 8.0.100-preview.7.23363.19
Commit: bef7f10d1d
Runtime Environment:
OS Name: Windows
OS Version: 10.0.22621
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\8.0.100-preview.7.23363.19\
Other information
No response