[flang] Enable optimizeEmptyElementals for BufferizeHLFIR pass. (#124982)

Enable the option under opt-for-speed. Elementals with shapes
like `(0, HUGE)` should run faster.

Author: vzakhari

flang/lib/Optimizer/Passes/Pipelines.cpp

@@ -245,7 +245,15 @@ void createHLFIRToFIRPassPipeline(mlir::PassManager &pm, bool enableOpenMP,
   }
   pm.addPass(hlfir::createLowerHLFIROrderedAssignments());
   pm.addPass(hlfir::createLowerHLFIRIntrinsics());
-  pm.addPass(hlfir::createBufferizeHLFIR());
+
+  hlfir::BufferizeHLFIROptions bufferizeOptions;
+  // For opt-for-speed, avoid running any of the loops resulting
+  // from hlfir.elemental lowering, if the result is an empty array.
+  // This helps to avoid long running loops for elementals with
+  // shapes like (0, HUGE).
+  if (optLevel.isOptimizingForSpeed())
+    bufferizeOptions.optimizeEmptyElementals = true;
+  pm.addPass(hlfir::createBufferizeHLFIR(bufferizeOptions));
   // Run hlfir.assign inlining again after BufferizeHLFIR,
   // because the latter may introduce new hlfir.assign operations,
   // e.g. for copying an array into a temporary due to