[flang][cuda] Change induction variable from i32 to index for doconcurrent inside cuf kernel directive (#129924)

Use `index` instead of `i32` for induction variables for doconcurrent
inside cuf kernel directive. Regular do loop inside cuf kernel directive
also uses `index`:
```
cuf.kernel<<<*, *>>> (%arg0 : index) = ...
```

Author: wangzpgi

flang/lib/Lower/Bridge.cpp

@@ -3150,10 +3150,9 @@ class FirConverter : public Fortran::lower::AbstractConverter {
               loc, 1); // Use index type directly
 
         // Ensure lb, ub, and step are of index type using fir.convert
-        mlir::Type indexType = builder->getIndexType();
-        lb = builder->create<fir::ConvertOp>(loc, indexType, lb);
-        ub = builder->create<fir::ConvertOp>(loc, indexType, ub);
-        step = builder->create<fir::ConvertOp>(loc, indexType, step);
+        lb = builder->create<fir::ConvertOp>(loc, idxTy, lb);
+        ub = builder->create<fir::ConvertOp>(loc, idxTy, ub);
+        step = builder->create<fir::ConvertOp>(loc, idxTy, step);
 
         lbs.push_back(lb);
         ubs.push_back(ub);
@@ -3163,18 +3162,14 @@ class FirConverter : public Fortran::lower::AbstractConverter {
 
         // Handle induction variable
         mlir::Value ivValue = getSymbolAddress(*name.symbol);
-        std::size_t ivTypeSize = name.symbol->size();
-        if (ivTypeSize == 0)
-          llvm::report_fatal_error("unexpected induction variable size");
-        mlir::Type ivTy = builder->getIntegerType(ivTypeSize * 8);
 
         if (!ivValue) {
           // DO CONCURRENT induction variables are not mapped yet since they are
           // local to the DO CONCURRENT scope.
           mlir::OpBuilder::InsertPoint insPt = builder->saveInsertionPoint();
           builder->setInsertionPointToStart(builder->getAllocaBlock());
           ivValue = builder->createTemporaryAlloc(
-              loc, ivTy, toStringRef(name.symbol->name()));
+              loc, idxTy, toStringRef(name.symbol->name()));
           builder->restoreInsertionPoint(insPt);
         }
 
@@ -3186,7 +3181,7 @@ class FirConverter : public Fortran::lower::AbstractConverter {
         // Bind the symbol to the declared variable
         bindSymbol(*name.symbol, ivValue);
         ivValues.push_back(ivValue);
-        ivTypes.push_back(ivTy);
+        ivTypes.push_back(idxTy);
         ivLocs.push_back(loc);
       }
     } else {

flang/test/Lower/CUDA/cuda-doconc.cuf

@@ -15,9 +15,9 @@ subroutine doconc1
 end
 
 ! CHECK: func.func @_QPdoconc1() {
-! CHECK: %[[DECL:.*]]:2 = hlfir.declare %{{.*}}#0 {uniq_name = "_QFdoconc1Ei"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+! CHECK: %[[DECL:.*]]:2 = hlfir.declare %{{.*}}#0 {uniq_name = "_QFdoconc1Ei"} : (!fir.ref<index>) -> (!fir.ref<index>, !fir.ref<index>)
 ! CHECK: cuf.kernel<<<*, *>>>
-! CHECK: %{{.*}} = fir.load %[[DECL]]#0 : !fir.ref<i32>
+! CHECK: %{{.*}} = fir.load %[[DECL]]#0 : !fir.ref<index>
 
 subroutine doconc2
   integer :: i, j, m, n
@@ -32,8 +32,8 @@ subroutine doconc2
 end
 
 ! CHECK: func.func @_QPdoconc2() {
-! CHECK: %[[DECLI:.*]]:2 = hlfir.declare %{{.*}}#0 {uniq_name = "_QFdoconc2Ei"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
-! CHECK: %[[DECLJ:.*]]:2 = hlfir.declare %{{.*}}#0 {uniq_name = "_QFdoconc2Ej"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
-! CHECK: cuf.kernel<<<*, *>>> (%arg0 : i32, %arg1 : i32) = (%{{.*}}, %{{.*}} : index, index) to (%{{.*}}, %{{.*}} : index, index)  step (%{{.*}}, %{{.*}} : index, index) {
-! CHECK: %{{.*}} = fir.load %[[DECLI]]#0 : !fir.ref<i32>
-! CHECK: %{{.*}} = fir.load %[[DECLJ]]#0 : !fir.ref<i32> 
+! CHECK: %[[DECLI:.*]]:2 = hlfir.declare %{{.*}}#0 {uniq_name = "_QFdoconc2Ei"} : (!fir.ref<index>) -> (!fir.ref<index>, !fir.ref<index>)
+! CHECK: %[[DECLJ:.*]]:2 = hlfir.declare %{{.*}}#0 {uniq_name = "_QFdoconc2Ej"} : (!fir.ref<index>) -> (!fir.ref<index>, !fir.ref<index>)
+! CHECK: cuf.kernel<<<*, *>>> (%arg0 : index, %arg1 : index) = (%{{.*}}, %{{.*}} : index, index) to (%{{.*}}, %{{.*}} : index, index)  step (%{{.*}}, %{{.*}} : index, index) {
+! CHECK: %{{.*}} = fir.load %[[DECLI]]#0 : !fir.ref<index>
+! CHECK: %{{.*}} = fir.load %[[DECLJ]]#0 : !fir.ref<index>