[flang][NFC] Fix invalid op result access

[clementval]

Summary

Fix invalid op result access. This will trigger
assertion introduced in D147883.

[PeteSteinfeld]

I had a few questions. But if none of them raise a red flag, all builds and tests correctly and looks good.

flang/lib/Lower/ConvertCall.cpp

223–224

This is the only place where sp gets an explicit value. Is this what you want?

407–416

Similarly, callResult only gets an explicit value if callNumResults is zero. Is this correct?

flang/lib/Lower/ConvertExpr.cpp

4279–4282

Similarly, outerRes doesn't always get an explicit value.

[clementval]

flang/lib/Lower/ConvertCall.cpp

223–224

Yes we want to get a value if there is actually a value. Otherwise it's just a null value.

407–416

When there is a value callNumResults != 0 we initialize callResult otherwise it is just a null mlir::Value

flang/lib/Lower/ConvertCall.cpp

if (!type.isa<fir::BoxType>()) {
       }
       resultLengths = lengths;
     }
 
     if (!extents.empty() || !lengths.empty()) {
       auto *bldr = &converter.getFirOpBuilder();
       auto stackSaveFn = fir::factory::getLlvmStackSave(builder);
       auto stackSaveSymbol = bldr->getSymbolRefAttr(stackSaveFn.getName());
-      mlir::Value sp = bldr->create<fir::CallOp>(
-                               loc, stackSaveFn.getFunctionType().getResults(),
-                               stackSaveSymbol, mlir::ValueRange{})
-                           .getResult(0);
+      mlir::Value sp;
+      fir::CallOp call = bldr->create<fir::CallOp>(
+          loc, stackSaveFn.getFunctionType().getResults(), stackSaveSymbol,
+          mlir::ValueRange{});
+      if (call.getNumResults() != 0)
+        sp = call.getResult(0);
       stmtCtx.attachCleanup([bldr, loc, sp]() {
         auto stackRestoreFn = fir::factory::getLlvmStackRestore(*bldr);
         auto stackRestoreSymbol =
             bldr->getSymbolRefAttr(stackRestoreFn.getName());
         bldr->create<fir::CallOp>(loc,
                                   stackRestoreFn.getFunctionType().getResults(),
                                   stackRestoreSymbol, mlir::ValueRange{sp});
       });
if (std::optional<unsigned> passArg = caller.getPassArgIndex()) {
           component->GetFirstSymbol(), &symMap);
       mlir::Value passObject = fir::getBase(pass);
       if (fir::isa_ref_type(passObject.getType()))
         passObject = builder.create<fir::LoadOp>(loc, passObject);
       dispatch = builder.create<fir::DispatchOp>(
           loc, funcType.getResults(), builder.getStringAttr(procName),
           passObject, operands, nullptr);
     }
-    callResult = dispatch.getResult(0);
     callNumResults = dispatch.getNumResults();
+    if (callNumResults != 0)
+      callResult = dispatch.getResult(0);
   } else {
     // Standard procedure call with fir.call.
     auto call = builder.create<fir::CallOp>(loc, funcType.getResults(),
                                             funcSymbolAttr, operands);
-    callResult = call.getResult(0);
     callNumResults = call.getNumResults();
+    if (callNumResults != 0)
+      callResult = call.getResult(0);
   }
 
   if (caller.mustSaveResult()) {
     assert(allocatedResult.has_value());
     builder.create<fir::SaveResultOp>(loc, callResult,
                                       fir::getBase(*allocatedResult),
                                       arrayResultShape, resultLengths);
   }
 

flang/lib/Lower/ConvertExpr.cpp

genImplicitLoops(mlir::ValueRange shape, mlir::Value innerArg) {
     auto currPt = builder.saveInsertionPoint();
     builder.setInsertionPointAfter(loops[0]);
     auto afterLoopNest = builder.saveInsertionPoint();
     builder.restoreInsertionPoint(currPt);
 
     // Put the implicit loop variables in row to column order to match FIR's
     // Ops. (The loops were constructed from outermost column to innermost
     // row.)
-    mlir::Value outerRes = loops[0].getResult(0);
+    mlir::Value outerRes;
+    if (loops[0].getNumResults() != 0)
+      outerRes = loops[0].getResult(0);
     return {IterationSpace(innerArg, outerRes, llvm::reverse(ivars)),
             afterLoopNest};
   }
 
   /// Build the iteration space into which the array expression will be lowered.
   /// The resultType is used to create a temporary, if needed.
   std::pair<IterationSpace, mlir::OpBuilder::InsertPoint>
   genIterSpace(mlir::Type resultType) {
     mlir::Location loc = getLoc();