[flang] Don't fold SIZE()/SHAPE() into expression referencing optiona…

…l dummy arguments

When computing the shape of an expression at compilation time as part of
folding an intrinsic function like SIZE(), don't create an expression that
increases a dependence on the presence of an optional dummy argument.

Differential Revision: https://reviews.llvm.org/D151737

flang/lib/Evaluate/shape.cpp

@@ -805,9 +805,19 @@ auto GetShapeHelper::operator()(const ProcedureRef &call) const -> Result {
   if (call.Rank() == 0) {
     return ScalarShape();
   } else if (call.IsElemental()) {
-    for (const auto &arg : call.arguments()) {
-      if (arg && arg->Rank() > 0) {
-        return (*this)(*arg);
+    // Use the shape of an actual array argument associated with a
+    // non-OPTIONAL dummy object argument.
+    if (context_) {
+      if (auto chars{characteristics::Procedure::FromActuals(
+              call.proc(), call.arguments(), *context_)}) {
+        std::size_t j{0};
+        for (const auto &arg : call.arguments()) {
+          if (arg && arg->Rank() > 0 && j < chars->dummyArguments.size() &&
+              !chars->dummyArguments[j].IsOptional()) {
+            return (*this)(*arg);
+          }
+          ++j;
+        }
       }
     }
     return ScalarShape();

flang/test/Evaluate/elem-shape.f90

@@ -0,0 +1,16 @@
+! RUN: %flang_fc1 -fdebug-unparse %s 2>&1 | FileCheck %s
+! Ensure that optional arguments aren't used to fold SIZE() or SHAPE()
+module m
+ contains
+  subroutine sub(x,y)
+    real :: x(:), y(:)
+    optional x
+    !CHECK: PRINT *, int(size(y,dim=1,kind=8),kind=4)
+    print *, size(f(x,y))
+  end
+  elemental function f(x,y)
+    real, intent(in) :: x, y
+    optional x
+    f = y
+  end
+end