[flang] [llvm] [flang] Implement SPLIT intrinsic subroutine with tests (PR #185584)

[Tarun Prabhu via llvm-commits]

================
@@ -8538,6 +8545,50 @@ void IntrinsicLibrary::genSleep(llvm::ArrayRef<fir::ExtendedValue> args) {
   fir::runtime::genSleep(builder, loc, fir::getBase(args[0]));
 }
 
+// SPLIT
+void IntrinsicLibrary::genSplit(llvm::ArrayRef<fir::ExtendedValue> args) {
+  assert(args.size() == 4 && "SPLIT requires 3 or 4 arguments");
+
+  // Handle required STRING base and length args
+  mlir::Value stringBase = fir::getBase(args[0]);
+  mlir::Value stringLen = fir::getLen(args[0]);
+
+  // Handle required SET string base and length args
+  mlir::Value setBase = fir::getBase(args[1]);
+  mlir::Value setLen = fir::getLen(args[1]);
+
+  // POS is INTENT(INOUT) - it's passed as an address
+  mlir::Value posAddr = fir::getBase(args[2]);
+
+  // Determine character kind
+  fir::KindTy kind =
+      fir::factory::CharacterExprHelper{builder, loc}.getCharacterKind(
+          stringBase.getType());
+
+  // Handle optional BACK argument
----------------
tarunprabhu wrote:

This is the one place where a comment would be helpful because an optional defaults to `.FALSE.` - something that is not obvious when one looks at the code.

https://github.com/llvm/llvm-project/pull/185584