---

This section details on the original issue you should resolve

<issue_title>No ReadOnlySpan static data optimization for new byte[N]</issue_title>
<issue_description>Version Used: dotnet 2.2.200-preview-009748

Steps to Reproduce:

Declare a static ReadOnlySpan<byte> property of the form:

public class C
{
 public static ReadOnlySpan<byte> StaticData => new byte[] { 0 };
 public static ReadOnlySpan<byte> DoesntWork => new byte[1];
} 

Expected Behavior:

Per the optimisation in #24621, I expected that both StaticData and DoesntWork would be compiled to a reference to static data, e.g., new ReadOnlySpan<byte>(&global::<PrivateImplementationDetails>.5BA93C9DB0CFF93F52B521D7420E43F6EDA2784F, 1);

Actual Behavior:

Only StaticData has the implementation optimisation; DoesntWork doesn't, even though it has the exact same data. The problem is more noticeable with an expression like new byte[1000], where you might not want to type out 1000 literal zero bytes in source code.

SharpLab: https://sharplab.io/#v2:D4AQDABCCMDcCwAoJIDMUBMEDCSDeSERU6MAbBAEoCmAhgCYDyAdgDYCeAygA63MA8AI3YAXagD4InEbREBLAMYARWbQgBeSc2oB3CMLEBtALoQ8ESAF8EiYiSjQKNBiw48+Q0RIhKA9tQBnZhEAdV8AJwBrDS1dfS9DaGMbSwggA===
</issue_description>

<agent_instructions>Copilot see if you can get this optimization working. Note that we already have the optimization somewhere in the compiler such that if you're initializing a static ReadOnlySpan<T> with an array with known values, that it will read that data out of the program data segment. What we want here is to make that work for when the user also uses the new T[size] form. This form is equivalent to new T[] { 0, 0, 0, ..., 0_size }, so it should get the same optimization.

</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@agocke I'm not really sure how this is an optimization. It's just trading binary size for allocations, isn't it? @agocke Yeah, I'm not sure the full consequences were appreciated when the issue was tagged. The original is definitely an optimization because the actual values in the initializer *must* be present in the binary, so that code just avoids an extra allocation.

This is more of a tradeoff and I think most people would much rather just allocate an empty block of memory, as opposed to making the binary bigger.

@gafter did you have a different opinion?</comment_new>
<comment_new>@VSadov
I think new T[constExpr] case was just overlooked.
The following means basically the same.

 public static ReadOnlySpan<byte> StaticData => new byte[] { 0, 0, 0 };
 public static ReadOnlySpan<byte> DoesntWork => new byte[3];

Readonly spans of zeroes are probably not very common and user can do new T[] {0,0,0}, if needed.
I think optimization could be extended to cover new T[] case just for consistency.

Assuming it is not common, it is probably not a big deal one way or another.</comment_new>
<comment_new>@agocke
Thanks @VSadov. I suppose the problem with making those the same thing is that you can't choose not to do the optimization. What would the suggestion be to defeat it? Store the array in a local first?</comment_new>
<comment_new>@agocke
I'll leave this one up to @gafter since I can see both an argument for consistency, but it also seems to be a trade-off that isn't directly in the "optimization" category.</comment_new>