[flang][NFC] Fix deprecation warning (#147932)

I started getting deprecation warnings from operations constructors
which seem to be doing implicit construction of mlir::ValueRange from a
std::nullopt by relying on implicit conversion from std::nullopt into
llvm::ArrayRef. ArrayRef{std::nullopt} is what has been deprecated.

Author: tblah

flang/lib/Optimizer/CodeGen/CodeGen.cpp

@@ -2239,18 +2239,17 @@ struct XReboxOpConversion : public EmboxCommonConversion<fir::cg::XReboxOp> {
         getSubcomponentIndices(rebox, rebox.getBox(), operands, fieldIndices);
       if (!rebox.getSubstr().empty())
         substringOffset = operands[rebox.getSubstrOperandIndex()];
-      base =
-          genBoxOffsetGep(rewriter, loc, base, llvmBaseObjectType, zero,
-                          /*cstInteriorIndices=*/llvm::ArrayRef<mlir::Value>(),
-                          fieldIndices, substringOffset);
+      base = genBoxOffsetGep(rewriter, loc, base, llvmBaseObjectType, zero,
+                             /*cstInteriorIndices=*/{}, fieldIndices,
+                             substringOffset);
     }
 
     if (rebox.getSlice().empty())
       // The array section is of the form array[%component][substring], keep
       // the input array extents and strides.
       return finalizeRebox(rebox, adaptor, destBoxTy, dest, base,
-                           /*lbounds*/ llvm::ArrayRef<mlir::Value>(),
-                           inputExtents, inputStrides, rewriter);
+                           /*lbounds*/ {}, inputExtents, inputStrides,
+                           rewriter);
 
     // The slice is of the form array(i:j:k)[%component]. Compute new extents
     // and strides.
@@ -2298,8 +2297,8 @@ struct XReboxOpConversion : public EmboxCommonConversion<fir::cg::XReboxOp> {
       }
     }
     return finalizeRebox(rebox, adaptor, destBoxTy, dest, base,
-                         /*lbounds*/ llvm::ArrayRef<mlir::Value>(),
-                         slicedExtents, slicedStrides, rewriter);
+                         /*lbounds*/ {}, slicedExtents, slicedStrides,
+                         rewriter);
   }
 
   /// Apply a new shape to the data described by a box given the base address,
@@ -3397,8 +3396,7 @@ static void genBrOp(A caseOp, mlir::Block *dest, std::optional<B> destOps,
   if (destOps)
     rewriter.replaceOpWithNewOp<mlir::LLVM::BrOp>(caseOp, *destOps, dest);
   else
-    rewriter.replaceOpWithNewOp<mlir::LLVM::BrOp>(
-        caseOp, llvm::ArrayRef<mlir::Value>(), dest);
+    rewriter.replaceOpWithNewOp<mlir::LLVM::BrOp>(caseOp, B{}, dest);
 }
 
 static void genCaseLadderStep(mlir::Location loc, mlir::Value cmp,

flang/lib/Optimizer/CodeGen/PreCGRewrite.cpp

@@ -107,9 +107,8 @@ class EmboxConversion : public mlir::OpRewritePattern<fir::EmboxOp> {
       shapeOpers.push_back(extVal);
     }
     auto xbox = rewriter.create<fir::cg::XEmboxOp>(
-        loc, embox.getType(), embox.getMemref(), shapeOpers,
-        llvm::ArrayRef<mlir::Value>(), llvm::ArrayRef<mlir::Value>(),
-        llvm::ArrayRef<mlir::Value>(), llvm::ArrayRef<mlir::Value>(),
+        loc, embox.getType(), embox.getMemref(), shapeOpers, mlir::ValueRange{},
+        mlir::ValueRange{}, mlir::ValueRange{}, mlir::ValueRange{},
         embox.getTypeparams(), embox.getSourceBox(),
         embox.getAllocatorIdxAttr());
     LLVM_DEBUG(llvm::dbgs() << "rewriting " << embox << " to " << xbox << '\n');