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

[Vedant Paranjape via llvm-commits]

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@@ -610,6 +639,45 @@ 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) {
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vedantparanjape-amd wrote:

@nikic the function https://github.com/llvm/llvm-project/blob/e4163c0927772f2ec73cf16d53e000614c419c45/llvm/lib/IR/Value.cpp#L731 pretty much runs a do-while loop and traverses the GEP tree to accumulate the offsets. If it encounters a bitcast (which it won't), it doesn't do much. So, I would want to ideally pull out just the traversal code out from the function, skipping the bitcasts code. But I think that can another patch, is it blocking this one ?

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