[flang-commits] [flang] [flang] Set LLVM specific attributes to fir.call's of Fortran runtime. (PR #128093)

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+//===- SetRuntimeCallAttributes.cpp ---------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+//===----------------------------------------------------------------------===//
+/// \file
+/// SetRuntimeCallAttributesPass looks for fir.call operations
+/// that are calling into Fortran runtime, and tries to set different
+/// attributes on them to enable more optimizations in LLVM backend
+/// (granted that they are preserved all the way to LLVM IR).
+/// This pass is currently only attaching fir.call wide atttributes,
+/// such as ones corresponding to llvm.memory, nosync, nocallbac, etc.
+/// It is not designed to attach attributes to the arguments and the results
+/// of a call.
+//===----------------------------------------------------------------------===//
+#include "flang/Common/static-multimap-view.h"
+#include "flang/Optimizer/Builder/Runtime/RTBuilder.h"
+#include "flang/Optimizer/Dialect/FIRDialect.h"
+#include "flang/Optimizer/Dialect/FIROpsSupport.h"
+#include "flang/Optimizer/Support/InternalNames.h"
+#include "flang/Optimizer/Transforms/Passes.h"
+#include "flang/Runtime/io-api-consts.h"
+#include "mlir/Dialect/LLVMIR/LLVMAttrs.h"
+
+namespace fir {
+#define GEN_PASS_DEF_SETRUNTIMECALLATTRIBUTES
+#include "flang/Optimizer/Transforms/Passes.h.inc"
+} // namespace fir
+
+#define DEBUG_TYPE "set-runtime-call-attrs"
+
+using namespace Fortran::runtime;
+using namespace Fortran::runtime::io;
+
+#define mkIOKey(X) FirmkKey(IONAME(X))
+#define mkRTKey(X) FirmkKey(RTNAME(X))
+
+// Return LLVM dialect MemoryEffectsAttr for the given Fortran runtime call.
+// This function is computing a generic value of this attribute
+// by analyzing the arguments and their types.
+// It tries to figure out if an "indirect" memory access is possible
+// during this call. If it is not possible, then the memory effects
+// are:
+//   * other = NoModRef
+//   * argMem = ModRef
+//   * inaccessibleMem = ModRef
+//
+// Otherwise, it returns an empty attribute meaning ModRef for all kinds
+// of memory.
+//
+// The attribute deduction is conservative in a sense that it applies
+// to most of the runtime calls, but it may still be incorrect for some
+// runtime calls.
+static mlir::LLVM::MemoryEffectsAttr getGenericMemoryAttr(fir::CallOp callOp) {
+  bool maybeIndirectAccess = false;
+  for (auto arg : callOp.getArgOperands()) {
+    mlir::Type argType = arg.getType();
+    if (mlir::isa<fir::BaseBoxType>(argType)) {
+      // If it is a null box, then this particular call
+      // cannot access memory indirectly through the box's
+      // base_addr.
+      auto def = arg.getDefiningOp();
+      if (!def || !mlir::isa<fir::ZeroOp>(def)) {
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jeanPerier wrote:

Maybe worth adding fir::AbsentOp here that is also used in some context to create null box.

https://github.com/llvm/llvm-project/pull/128093