[Flang][OpenMP] Don't expect block arguments using early privatization (#105842)

There are some spots where all symbols to privatize collected by a
`DataSharingProcessor` instance are expected to have corresponding entry
block arguments associated regardless of whether delayed privatization
was enabled.

This can result in compiler crashes if a `DataSharingProcessor` instance
created with `useDelayedPrivatization=false` is queried in this way. The
solution proposed by this patch is to provide another public method to
query specifically delayed privatization symbols, which will either be
empty or point to the complete set of symbols to privatize accordingly.

Author: skatrak

flang/lib/Lower/OpenMP/DataSharingProcessor.h

@@ -153,6 +153,12 @@ class DataSharingProcessor {
   getAllSymbolsToPrivatize() const {
     return allPrivatizedSymbols;
   }
+
+  llvm::ArrayRef<const semantics::Symbol *> getDelayedPrivSymbols() const {
+    return useDelayedPrivatization
+               ? allPrivatizedSymbols.getArrayRef()
+               : llvm::ArrayRef<const semantics::Symbol *>();
+  }
 };
 
 } // namespace omp

flang/lib/Lower/OpenMP/OpenMP.cpp

@@ -882,7 +882,7 @@ static void genBodyOfTargetOp(
   }
 
   for (auto [argIndex, argSymbol] :
-       llvm::enumerate(dsp.getAllSymbolsToPrivatize())) {
+       llvm::enumerate(dsp.getDelayedPrivSymbols())) {
     argIndex = mapSyms.size() + argIndex;
 
     const mlir::BlockArgument &arg = region.getArgument(argIndex);
@@ -1494,8 +1494,8 @@ genParallelOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
                              allRegionArgLocs);
 
     llvm::SmallVector<const semantics::Symbol *> allSymbols(reductionSyms);
-    allSymbols.append(dsp.getAllSymbolsToPrivatize().begin(),
-                      dsp.getAllSymbolsToPrivatize().end());
+    allSymbols.append(dsp.getDelayedPrivSymbols().begin(),
+                      dsp.getDelayedPrivSymbols().end());
 
     unsigned argIdx = 0;
     for (const semantics::Symbol *arg : allSymbols) {