[llvm] [ArgPromotion] Handle pointer arguments of recursive calls (PR #78735)

[Nikita Popov via llvm-commits]

================
@@ -610,6 +638,45 @@ static bool findArgParts(Argument *Arg, const DataLayout &DL, AAResults &AAR,
       // unknown users
     }
 
+    auto *CB = dyn_cast<CallBase>(V);
+    Value *PtrArg = cast<Value>(U);
+    if (CB && PtrArg && CB->getCalledFunction() == CB->getFunction()) {
+      Type *PtrTy = PtrArg->getType();
+      APInt Offset(DL.getIndexTypeSizeInBits(PtrTy), 0);
+      PtrArg = PtrArg->stripAndAccumulateConstantOffsets(
+          DL, Offset,
+          /* AllowNonInbounds= */ true);
+      if (PtrArg != Arg)
+        return false;
+
+      if (Offset.getSignificantBits() >= 64)
+        return false;
+
+      int64_t Off = Offset.getSExtValue();
+      if (Off) {
+        LLVM_DEBUG(dbgs() << "ArgPromotion of " << *Arg << " failed: "
+                          << "pointer offset is not equal to zero\n");
+        return false;
+      }
----------------
nikic wrote:

Let me spell this out explicitly. Here is the change you should do:
```suggestion
      if (PtrArg != Arg)
        return false;
```


https://github.com/llvm/llvm-project/pull/78735