[llvm] [NFC][DebugInfo] Wrap DILineInfo return type with std::optional to handle missing debug info. (PR #129792)

[David Blaikie via llvm-commits]

================
@@ -728,8 +728,11 @@ llvm::Error DwarfTransformer::verify(StringRef GsymPath,
           DICtx.getInliningInfoForAddress(SectAddr, DLIS);
       uint32_t NumDwarfInlineInfos = DwarfInlineInfos.getNumberOfFrames();
       if (NumDwarfInlineInfos == 0) {
-        DwarfInlineInfos.addFrame(
-            DICtx.getLineInfoForAddress(SectAddr, DLIS));
+        if (std::optional<DILineInfo> DwarfLineInfo =
+                DICtx.getLineInfoForAddress(SectAddr, DLIS))
+          DwarfInlineInfos.addFrame(*DwarfLineInfo);
+        else
+          DwarfInlineInfos.addFrame(DILineInfo());
----------------
dwblaikie wrote:

Perhaps this and other places could use std::optional's `value_or`, like:
```
DWARFLineInfos.addFrame(DICtx.getLineInfoForAddress(...).value_or(DILineInfo()));
```
It might be easier to split this into several simpler mechanical changes, for instance - one change could change the API signature, but not the behavior (so adds std::optional, but always returns a present optional with the same values as the old API - all callers could dereference that optional unconditionally - or may be simpler to migrate every caller to the `value_or` shown above, that way out of tree updates will only have to happen once to preserve the existing behavior), then change the behavior to differentiate the cases of interest (& test that newly exposed behavior/differentiation between line zero and nullopt - either plumbing it all the way through to llvm-symbolizer in that change, or doing the plumbing separately (but doing some API testing, if the plumbing is going to be done separately)).

https://github.com/llvm/llvm-project/pull/129792