<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/78278>78278</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [SPIRV] Global unnamed variables cause SPIR-V Backend code generation to crash
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          VyacheslavLevytskyy
      </td>
    </tr>
</table>

<pre>
    Unnamed global variables (represented as an unsigned numeric value with @ prefix, e.g., @0) cause code generation to crash (assert in Debug, undefined behaviour in Release builds). An example of such a behaviour presents the following ll code:

```
@0 = addrspace(1) global i8 123
; Function Attrs: nounwind
define spir_kernel void @foo() #0 {
  ret void
}
attributes #0 = { nounwind }
```

Further investigation and debug show the culprit as Instruction Select pass (after legalizer). The reason for the crash is that `GlobalValue`'s `getGlobalIdentifier()` would fail for unnamed globals when trying to access the first character of the name.

There are two possible approaches for a local fix of the issue:
- add a special case of empty name in global variables (pass empty string, check for it when generating linkage decoration, etc.),
- generate a name of a global variable, as in case of other Target implementation (see: lib/IR/Mangler.cpp:131 and code generation for `llc -o` generates `.globl __unnamed_1`  and `__unnamed_1:` for `@0`).

Complexity of two fixes is similar, both are local fixes, and the latter seems a better solution due to the intricacy of expected linkage attributes for unnamed global variables (see, for example, https://discourse.llvm.org/t/naming-and-linkage-for-llvm-ir-anonymous-globals/61595). It's expected that by default a global variable is an external linkage symbol, and both left its name empty and don't generate external linkage attribute would cause to a disputable resolution. Probably, a better fix is to generate a name for an unnamed global in a style of lib/IR/Mangler.cpp:131
</pre>
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