[llvm] [licm] clone metadata when hoisting conditional branch (PR #152232)

[Snehasish Kumar via llvm-commits]

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@@ -857,9 +859,18 @@ class ControlFlowHoister {
     }
 
     // Now finally clone BI.
-    ReplaceInstWithInst(
-        HoistTarget->getTerminator(),
-        BranchInst::Create(HoistTrueDest, HoistFalseDest, BI->getCondition()));
+    auto *NewBI =
+        BranchInst::Create(HoistTrueDest, HoistFalseDest, BI->getCondition(),
+                           HoistTarget->getTerminator()->getIterator());
+    HoistTarget->getTerminator()->eraseFromParent();
+    // Copy all the metadata. In particular:
+    // - debug info (critical to Sample-based profiling) should be the same
+    // as the original branch, not that of HoistTarget->getTerminator(),
+    // which is what ReplaceInstWithInst would use.
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snehasish wrote:

Filed #152767 to track the addition of a new flag and to update the documentation. 

I don't think we should enable it by default for O2/O3 though. I received pushback even when suggesting we add it under `-fdebug-info-for-profiling`. It should be purely opt-in especially for the cases where the location may be non-representable.

To keep this PR moving along can we leave the behaviour for debug information unchanged (add a TODO with the issue number) and only address the profile metadata being dropped?

https://github.com/llvm/llvm-project/pull/152232