[flang] Convert assertion to a TODO

[clementval]

Summary

The original assertion is not necessarily correct since the shape
argument may involve a slice of an array (an expression) and not a whole
vector with constant length. In the presence of a slice operation, the
size must be computed (left as a TODO for now).

This patch is part of the upstreaming effort from fir-dev branch.

Co-authored-by: Eric Schweitz <[e-mail]>

flang/lib/Lower/IntrinsicCall.cpp

IntrinsicLibrary::genReshape(mlir::Type resultType,
   // Handle source argument
   mlir::Value source = builder.createBox(loc, args[0]);
 
   // Handle shape argument
   mlir::Value shape = builder.createBox(loc, args[1]);
   assert(fir::BoxValue(shape).rank() == 1);
   mlir::Type shapeTy = shape.getType();
   mlir::Type shapeArrTy = fir::dyn_cast_ptrOrBoxEleTy(shapeTy);
-  auto resultRank = shapeArrTy.cast<fir::SequenceType>().getShape();
+  auto resultRank = shapeArrTy.cast<fir::SequenceType>().getShape()[0];
 
-  assert(resultRank[0] != fir::SequenceType::getUnknownExtent() &&
-         "shape arg must have constant size");
+  if (resultRank == fir::SequenceType::getUnknownExtent())
+    TODO(loc, "RESHAPE intrinsic requires computing rank of result");
 
   // Handle optional pad argument
   mlir::Value pad = isStaticallyAbsent(args[2])
                         ? builder.create<fir::AbsentOp>(
                               loc, fir::BoxType::get(builder.getI1Type()))
                         : builder.createBox(loc, args[2]);
 
   // Handle optional order argument
   mlir::Value order = isStaticallyAbsent(args[3])
                           ? builder.create<fir::AbsentOp>(
                                 loc, fir::BoxType::get(builder.getI1Type()))
                           : builder.createBox(loc, args[3]);
 
   // Create mutable fir.box to be passed to the runtime for the result.
-  mlir::Type type = builder.getVarLenSeqTy(resultType, resultRank[0]);
+  mlir::Type type = builder.getVarLenSeqTy(resultType, resultRank);
   fir::MutableBoxValue resultMutableBox =
       fir::factory::createTempMutableBox(builder, loc, type);
 
   mlir::Value resultIrBox =
       fir::factory::getMutableIRBox(builder, loc, resultMutableBox);
 
   fir::runtime::genReshape(builder, loc, resultIrBox, source, shape, pad,
                            order);