[llvm] [AIX] Handle arbitrary sized integers when lowering formal arguments passed on the stack (PR #149351)

[David Tenty via llvm-commits]

================
@@ -7296,9 +7296,19 @@ SDValue PPCTargetLowering::LowerFormalArguments_AIX(
       if (!ArgVT.isVector() && !ValVT.isVector() && ArgVT.isInteger() &&
           ValVT.isInteger() &&
           ArgVT.getScalarSizeInBits() < ValVT.getScalarSizeInBits()) {
-        SDValue ArgValueTrunc = DAG.getNode(
-            ISD::TRUNCATE, dl, ArgVT.getSimpleVT() == MVT::i1 ? MVT::i8 : ArgVT,
-            ArgValue);
+        // It is possible to have either real integer values that aren't
+        // the power of two sizes, or integers that were not originally
+        // integers. In the latter case, these could have came from structs,
+        // and these integers would not have an extend on the parameter.
+        // Since these types of integers do not have an extend specified
+        // in the first place, the type of extend that we do should not matter.
+        EVT TruncatedArgVT;
+        if (ArgVT.isSimple())
+          TruncatedArgVT = ArgVT.getSimpleVT() == MVT::i1 ? MVT::i8 : ArgVT;
+        else
+          TruncatedArgVT = ArgVT;
----------------
daltenty wrote:

nit: this could simplify, since the default is to return ArgVT:
```suggestion
        TruncatedArgVT = ArgVT.isSimple() && ArgVT.getSimpleVT() == MVT::i1 ? MVT::i8 : ArgVT;
```

I like writing it this way, because it makes clear that the only real remaining special case is i1's.

https://github.com/llvm/llvm-project/pull/149351