[compiler-rt] [llvm] [JITLink][Mips] Add ELF backend (PR #224578)

[Lang Hames via llvm-commits]

================
@@ -1028,13 +1028,13 @@ class LinkGraph {
 
   LinkGraph(std::string Name, std::shared_ptr<orc::SymbolStringPool> SSP,
             Triple TT, SubtargetFeatures Features,
-            GetEdgeKindNameFunction GetEdgeKindName)
+            GetEdgeKindNameFunction GetEdgeKindName,
+            std::optional<unsigned> PointerSize = std::nullopt)
       : Name(std::move(Name)), SSP(std::move(SSP)), TT(std::move(TT)),
         Features(std::move(Features)),
-        GetEdgeKindName(std::move(GetEdgeKindName)) {
-    assert(!(Triple::getArchPointerBitWidth(this->TT.getArch()) % 8) &&
----------------
lhames wrote:

My first reaction is that we'd be better off adding a defaulted `StringRef ABIName = ""` argument: if it's non-empty, we generate a data-layout string and pulling the pointer size out of that, and as a bonus we can report the LinkGraph's ABI, which might be helpful in other contexts. On the flip side we'd have to find a way to feed this through -- it's not part of the top-level JITLink APIs at the moment.

Just to check that I understand from the changes to `ELFLinkGraphBuilder.h`:
```c++
ELFT::Is64Bits ? 8 : 4
```
Are mips64 N32 objects ELF32? Are there mips64 objects that are ELF64? How would they be handled?

https://github.com/llvm/llvm-project/pull/224578