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

This change is inspired by a case in facerec benchmark, where
performance
of scalar code may improve by about 6%@aarch64 due to getting rid of
redundant
loads from Fortran descriptors. These descriptors are corresponding
to subroutine local ALLOCATABLE, SAVE variables. The scalar loop nest
in LocalMove subroutine contains call to Fortran runtime IO functions,
and LLVM globals-aa analysis cannot prove that these calls do not modify
the globalized descriptors with internal linkage.

This patch sets and propagates llvm.memory_effects attribute for
fir.call
operations calling Fortran runtime functions. In particular, it tries
to set the Other memory effect to NoModRef. The Other memory effect
includes accesses to globals and captured pointers, so we cannot set
it for functions taking Fortran descriptors with one exception
for calls where the Fortran descriptor arguments are all null.

As long as different calls to the same Fortran runtime function may have
different attributes, I decided to attach the attributes to the calls
rather than functions. Moreover, attaching the attributes to func.func
will require propagating these attributes to llvm.func, which is not
happening right now.

In addition to llvm.memory_effects, the new pass sets llvm.nosync
and llvm.nocallback attributes that may also help LLVM alias analysis
(e.g. see #127707). These attributes are ignored currently.
I will support them in LLVM IR dialect in a separate patch.

I also added another pass for developers to be able to print
declarations/calls of all Fortran runtime functions that are recognized
by the attributes setting pass. It should help with maintenance
of the LIT tests.

1 files changed, 106 insertions, 0 deletions

diff --git a/flang/lib/Optimizer/Transforms/GenRuntimeCallsForTest.cpp b/flang/lib/Optimizer/Transforms/GenRuntimeCallsForTest.cpp
new file mode 100644
index 000000000000..8d1d62e334d8
--- /dev/null
+++ b/flang/lib/Optimizer/Transforms/GenRuntimeCallsForTest.cpp
@@ -0,0 +1,106 @@
+//===- GenRuntimeCallsForTest.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
+/// This pass is only for developers to generate declarations/calls
+/// of Fortran runtime function recognized in
+/// flang/Optimizer/Transforms/RuntimeFunctions.inc table.
+/// Sample of the generated FIR:
+///   func.func private
+///       @_FortranAioSetStatus(!fir.ref<i8>, !fir.ref<i8>, i64) ->
+///       i1 attributes {fir.io, fir.runtime}
+///
+///   func.func @test__FortranAioSetStatus(
+///       %arg0: !fir.ref<i8>, %arg1: !fir.ref<i8>, %arg2: i64) -> i1 {
+///    %0 = fir.call @_FortranAioSetStatus(%arg0, %arg1, %arg2) :
+///        (!fir.ref<i8>, !fir.ref<i8>, i64) -> i1
+///    return %0 : i1
+///  }
+//===----------------------------------------------------------------------===//
+#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_GENRUNTIMECALLSFORTEST
+#include "flang/Optimizer/Transforms/Passes.h.inc"
+} // namespace fir
+
+#define DEBUG_TYPE "gen-runtime-calls-for-test"
+
+using namespace Fortran::runtime;
+using namespace Fortran::runtime::io;
+
+#define mkIOKey(X) FirmkKey(IONAME(X))
+#define mkRTKey(X) FirmkKey(RTNAME(X))
+
+namespace {
+class GenRuntimeCallsForTestPass
+    : public fir::impl::GenRuntimeCallsForTestBase<GenRuntimeCallsForTestPass> {
+  using GenRuntimeCallsForTestBase<
+      GenRuntimeCallsForTestPass>::GenRuntimeCallsForTestBase;
+
+public:
+  void runOnOperation() override;
+};
+} // end anonymous namespace
+
+static constexpr llvm::StringRef testPrefix = "test_";
+
+void GenRuntimeCallsForTestPass::runOnOperation() {
+  mlir::ModuleOp moduleOp = getOperation();
+  mlir::OpBuilder mlirBuilder(moduleOp.getRegion());
+  fir::FirOpBuilder builder(mlirBuilder, moduleOp);
+  mlir::Location loc = mlir::UnknownLoc::get(builder.getContext());
+
+#define KNOWN_IO_FUNC(X)                                                       \
+  fir::runtime::getIORuntimeFunc<mkIOKey(X)>(loc, builder)
+#define KNOWN_RUNTIME_FUNC(X)                                                  \
+  fir::runtime::getRuntimeFunc<mkRTKey(X)>(loc, builder)
+
+  mlir::func::FuncOp runtimeFuncsTable[] = {
+#include "flang/Optimizer/Transforms/RuntimeFunctions.inc"
+  };
+
+  if (!doGenerateCalls)
+    return;
+
+  // Generate thin wrapper functions calling the known Fortran
+  // runtime functions.
+  llvm::SmallVector<mlir::Operation *> newFuncs;
+  for (unsigned i = 0;
+       i < sizeof(runtimeFuncsTable) / sizeof(runtimeFuncsTable[0]); ++i) {
+    mlir::func::FuncOp funcOp = runtimeFuncsTable[i];
+    mlir::FunctionType funcTy = funcOp.getFunctionType();
+    std::string name = (llvm::Twine(testPrefix) + funcOp.getName()).str();
+    mlir::func::FuncOp callerFunc = builder.createFunction(loc, name, funcTy);
+    callerFunc.setVisibility(mlir::SymbolTable::Visibility::Public);
+    mlir::OpBuilder::InsertPoint insertPt = builder.saveInsertionPoint();
+
+    // Generate the wrapper function body that consists of a call and return.
+    builder.setInsertionPointToStart(callerFunc.addEntryBlock());
+    mlir::Block::BlockArgListType args = callerFunc.front().getArguments();
+    auto callOp = builder.create<fir::CallOp>(loc, funcOp, args);
+    builder.create<mlir::func::ReturnOp>(loc, callOp.getResults());
+
+    newFuncs.push_back(callerFunc.getOperation());
+    builder.restoreInsertionPoint(insertPt);
+  }
+
+  // Make sure all wrapper functions are at the beginning
+  // of the module.
+  auto moduleBegin = moduleOp.getBody()->begin();
+  for (auto func : newFuncs)
+    func->moveBefore(moduleOp.getBody(), moduleBegin);
+}