[llvm] [DebugInfo] Preserve line and column number when merging debug info. (PR #129960)

[Snehasish Kumar via llvm-commits]

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@@ -125,6 +132,20 @@ DILocation *DILocation::getMergedLocation(DILocation *LocA, DILocation *LocB) {
   if (LocA == LocB)
     return LocA;
 
+  // For some use cases (SamplePGO), it is important to retain distinct source
+  // locations. When this flag is set, we choose arbitrarily between A and B,
+  // rather than computing a merged location using line 0, which is typically
+  // not useful for PGO.
+  if (PickMergedSourceLocations) {
+    auto A = std::make_tuple(LocA->getLine(), LocA->getColumn(),
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snehasish wrote:

No, the only place it would be useful is if `getFilename` and `getDirectory` returned string, but they return StringRef. Also you'd have to rewrite this to do the comparison without the `auto A` and `auto B` vars or you'd introduce lifetime issues if you just replaced `make_tuple` with `forward_as_tuple`. 

https://github.com/llvm/llvm-project/pull/129960