[flang-commits] [flang] [flang] Fix bogus error about procedure incompatbility (PR #107645)

[via flang-commits]

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@@ -1088,24 +1088,42 @@ Expr<T> FoldMINorMAX(
   static_assert(T::category == TypeCategory::Integer ||
       T::category == TypeCategory::Real ||
       T::category == TypeCategory::Character);
-  std::vector<Constant<T> *> constantArgs;
-  // Call Folding on all arguments, even if some are not constant,
-  // to make operand promotion explicit.
-  for (auto &arg : funcRef.arguments()) {
-    if (auto *cst{Folder<T>{context}.Folding(arg)}) {
-      constantArgs.push_back(cst);
+  auto &args{funcRef.arguments()};
+  bool ok{true};
+  std::optional<Expr<T>> result;
+  Folder<T> folder{context};
+  for (std::optional<ActualArgument> &arg : args) {
+    // Call Folding on all arguments to make operand promotion explicit.
+    if (!folder.Folding(arg)) {
+      // TODO: Lowering can't handle having every FunctionRef for max and min
+      // being converted into Extremum<T>.  That needs fixing.  Until that
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jeanPerier wrote:

Do you have sources for such cases. I wonder if this has to do with the handling of optional arguments to min/max that is not done for Extremum<T>.

I am not sure the folding here would  properly deal with such optional arguments anyway since `max(a,b,c)` is not equivalent to `max(max(a,b), c)` as far as optionals are concerned.

Extremum<T> for characters is also [unimplemented](https://github.com/llvm/llvm-project/blob/db6051dae085c35020c1273ae8d38508c9958bc7/flang/lib/Lower/ConvertExprToHLFIR.cpp#L1046) since it was not easily testable so far. 

Otherwise, unconditional folding for numerical with two arguments should "just work", and it is indeed a bug if it does not.

https://github.com/llvm/llvm-project/pull/107645