[llvm] [DropUnnecessaryAssumes] Make the ephemeral value check more precise (PR #160700)

[Ramkumar Ramachandra via llvm-commits]

================
@@ -17,13 +18,48 @@ using namespace llvm;
 using namespace llvm::PatternMatch;
 
 static bool affectedValuesAreEphemeral(ArrayRef<Value *> Affected) {
-  // If all the affected uses have only one use (part of the assume), then
-  // the assume does not provide useful information. Note that additional
-  // users may appear as a result of inlining and CSE, so we should only
-  // make this assumption late in the optimization pipeline.
-  // TODO: Handle dead cyclic usages.
-  // TODO: Handle multiple dead assumes on the same value.
-  return all_of(Affected, match_fn(m_OneUse(m_Value())));
+  // Check whether all the uses are ephemeral, i.e. recursively only used
+  // by assumes. In that case, the assume does not provide useful information.
+  // Note that additional users may appear as a result of inlining and CSE,
+  // so we should only make this assumption late in the optimization pipeline.
+  SmallSetVector<Instruction *, 32> Worklist;
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artagnon wrote:

```suggestion
  SmallVector<Instruction *, 32> Worklist;
```

Does it need to be a set?

https://github.com/llvm/llvm-project/pull/160700