[flang][NFC] move loadIfRef to FIRBuilder (#84306)

This will be useful for OpenMP too.

I changed the definition slightly to use `fir::isa_ref_type` (which also
includes llvm pointers) because I think it reads better using the common
type helpers. There shouldn't be any llvm pointers in lowering so this
isn't a functional change.

flang/include/flang/Optimizer/Builder/FIRBuilder.h

@@ -309,6 +309,10 @@ class FirOpBuilder : public mlir::OpBuilder, public mlir::OpBuilder::Listener {
   void createStoreWithConvert(mlir::Location loc, mlir::Value val,
                               mlir::Value addr);
 
+  /// Create a fir.load if \p val is a reference or pointer type. Return the
+  /// result of the load if it was created, otherwise return \p val
+  mlir::Value loadIfRef(mlir::Location loc, mlir::Value val);
+
   /// Create a new FuncOp. If the function may have already been created, use
   /// `addNamedFunction` instead.
   mlir::func::FuncOp createFunction(mlir::Location loc, llvm::StringRef name,

flang/lib/Lower/OpenACC.cpp

@@ -1041,14 +1041,6 @@ static mlir::Value genLogicalCombiner(fir::FirOpBuilder &builder,
   return builder.create<fir::ConvertOp>(loc, value1.getType(), combined);
 }
 
-static mlir::Value loadIfRef(fir::FirOpBuilder &builder, mlir::Location loc,
-                             mlir::Value value) {
-  if (mlir::isa<fir::ReferenceType, fir::PointerType, fir::HeapType>(
-          value.getType()))
-    return builder.create<fir::LoadOp>(loc, value);
-  return value;
-}
-
 static mlir::Value genComparisonCombiner(fir::FirOpBuilder &builder,
                                          mlir::Location loc,
                                          mlir::arith::CmpIPredicate pred,
@@ -1066,8 +1058,8 @@ static mlir::Value genScalarCombiner(fir::FirOpBuilder &builder,
                                      mlir::acc::ReductionOperator op,
                                      mlir::Type ty, mlir::Value value1,
                                      mlir::Value value2) {
-  value1 = loadIfRef(builder, loc, value1);
-  value2 = loadIfRef(builder, loc, value2);
+  value1 = builder.loadIfRef(loc, value1);
+  value2 = builder.loadIfRef(loc, value2);
   if (op == mlir::acc::ReductionOperator::AccAdd) {
     if (ty.isIntOrIndex())
       return builder.create<mlir::arith::AddIOp>(loc, value1, value2);

flang/lib/Optimizer/Builder/FIRBuilder.cpp

@@ -16,6 +16,7 @@
 #include "flang/Optimizer/Builder/Todo.h"
 #include "flang/Optimizer/Dialect/FIRAttr.h"
 #include "flang/Optimizer/Dialect/FIROpsSupport.h"
+#include "flang/Optimizer/Dialect/FIRType.h"
 #include "flang/Optimizer/Support/FatalError.h"
 #include "flang/Optimizer/Support/InternalNames.h"
 #include "mlir/Dialect/LLVMIR/LLVMDialect.h"
@@ -404,6 +405,12 @@ void fir::FirOpBuilder::createStoreWithConvert(mlir::Location loc,
   create<fir::StoreOp>(loc, cast, addr);
 }
 
+mlir::Value fir::FirOpBuilder::loadIfRef(mlir::Location loc, mlir::Value val) {
+  if (fir::isa_ref_type(val.getType()))
+    return create<fir::LoadOp>(loc, val);
+  return val;
+}
+
 fir::StringLitOp fir::FirOpBuilder::createStringLitOp(mlir::Location loc,
                                                       llvm::StringRef data) {
   auto type = fir::CharacterType::get(getContext(), 1, data.size());