[llvm-branch-commits] [llvm] [DSE] Make DSE eliminate stores to objects with a sized dead_on_return (PR #173694)

[Antonio Frighetto via llvm-branch-commits]

================
@@ -1016,11 +1017,18 @@ struct DSEState {
 
     // Treat byval, inalloca or dead on return arguments the same as Allocas,
     // stores to them are dead at the end of the function.
-    for (Argument &AI : F.args())
+    for (Argument &AI : F.args()) {
       if (AI.hasPassPointeeByValueCopyAttr() ||
           (AI.getType()->isPointerTy() &&
            AI.getDeadOnReturnInfo().coversAllReachableMemory()))
         InvisibleToCallerAfterRet.insert({&AI, true});
+      if (AI.getType()->isPointerTy() &&
+          !AI.getDeadOnReturnInfo().coversAllReachableMemory()) {
+        if (uint64_t DeadOnReturnBytes =
+                AI.getDeadOnReturnInfo().getNumberOfDeadBytes())
+          InvisibleToCallerAfterRetBounded.insert({&AI, DeadOnReturnBytes});
+      }
+    }
----------------
antoniofrighetto wrote:

Perhaps the code could be reordered a bit here, I'd favour readability:
```cpp
for (Argument &AI : F.args()) {
  if (AI.hasPassPointeeByValueCopyAttr()) {
    InvisibleToCallerAfterRet.insert({&AI, true});
    continue;
  }

  if (!AI.getType()->isPointerTy())
    continue;

  const auto &Info = AI.getDeadOnReturnInfo();
  if (Info.coversAllReachableMemory())
    InvisibleToCallerAfterRet.insert({&AI, true});
  else if (uint64_t DeadBytes = Info.getNumberOfDeadBytes())
    InvisibleToCallerAfterRetBounded.insert({&AI, DeadBytes});
}
```

https://github.com/llvm/llvm-project/pull/173694