[llvm] [SystemZ] Handle IR struct arguments correctly. (PR #169583)

[Ulrich Weigand via llvm-commits]

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@@ -2074,16 +2096,26 @@ SDValue SystemZTargetLowering::LowerFormalArguments(
                                    MachinePointerInfo()));
       // If the original argument was split (e.g. i128), we need
       // to load all parts of it here (using the same address).
-      unsigned ArgIndex = Ins[I].OrigArgIndex;
-      assert (Ins[I].PartOffset == 0);
-      while (I + 1 != E && Ins[I + 1].OrigArgIndex == ArgIndex) {
-        CCValAssign &PartVA = ArgLocs[I + 1];
-        unsigned PartOffset = Ins[I + 1].PartOffset;
-        SDValue Address = DAG.getNode(ISD::ADD, DL, PtrVT, ArgValue,
-                                      DAG.getIntPtrConstant(PartOffset, DL));
-        InVals.push_back(DAG.getLoad(PartVA.getValVT(), DL, Chain, Address,
-                                     MachinePointerInfo()));
-        ++I;
+      MVT PartVT;
+      unsigned NumParts;
+      if (analyzeArgSplit(Ins, ArgLocs, I, PartVT, NumParts)) {
+        // TODO: It is strange that while LowerCallTo() sets the PartOffset
+        // relative to the first split part LowerArguments() sets the offset
+        // from the beginning of the struct. So with {i32, i256}, the
+        // PartOffset for the i256 parts are differently handled. Try to
+        // remove that difference and use PartOffset directly here (instead
+        // of SplitBaseOffs).
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uweigand wrote:

Yes, probably best to open an issue and as Tom Stellard if he remembers the background, and maybe pull in some other maintainers in that area ...   But definitely as follow up.

https://github.com/llvm/llvm-project/pull/169583