[flang-commits] [flang] [flang] Apply nocapture attribute to dummy arguments (PR #116182)

[via flang-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-flang-fir-hlfir

Author: None (s-watanabe314)

<details>
<summary>Changes</summary>

Apply llvm.nocapture attribute to dummy arguments that do not have the target, asynchronous, volatile, or pointer attributes in a procedure that is not a bind(c). This was discussed in

https://discourse.llvm.org/t/applying-the-nocapture-attribute-to-reference-passed-arguments-in-fortran-subroutines/81401

---
Full diff: https://github.com/llvm/llvm-project/pull/116182.diff


2 Files Affected:

- (modified) flang/lib/Optimizer/Transforms/FunctionAttr.cpp (+21) 
- (added) flang/test/Transforms/function-attrs.fir (+45) 


``````````diff
diff --git a/flang/lib/Optimizer/Transforms/FunctionAttr.cpp b/flang/lib/Optimizer/Transforms/FunctionAttr.cpp
index 69c41595974ef9..8b1aef38cc0267 100644
--- a/flang/lib/Optimizer/Transforms/FunctionAttr.cpp
+++ b/flang/lib/Optimizer/Transforms/FunctionAttr.cpp
@@ -10,6 +10,8 @@
 /// \file
 /// This is a generic pass for adding attributes to functions.
 //===----------------------------------------------------------------------===//
+#include "flang/Optimizer/Dialect/FIROpsSupport.h"
+#include "flang/Optimizer/Support/InternalNames.h"
 #include "flang/Optimizer/Transforms/Passes.h"
 #include "mlir/Dialect/LLVMIR/LLVMAttrs.h"
 #include "mlir/Dialect/LLVMIR/LLVMDialect.h"
@@ -45,6 +47,25 @@ void FunctionAttrPass::runOnOperation() {
 
   LLVM_DEBUG(llvm::dbgs() << "Func-name:" << func.getSymName() << "\n");
 
+  llvm::StringRef name = func.getSymName();
+  auto deconstructed = fir::NameUniquer::deconstruct(name);
+  bool isFromModule = !deconstructed.second.modules.empty();
+
+  if ((isFromModule || !func.isDeclaration()) &&
+      !fir::hasBindcAttr(func.getOperation())) {
+    llvm::StringRef nocapture = mlir::LLVM::LLVMDialect::getNoCaptureAttrName();
+    mlir::UnitAttr unitAttr = mlir::UnitAttr::get(func.getContext());
+
+    for (auto [index, argType] : llvm::enumerate(func.getArgumentTypes())) {
+      if (mlir::isa<fir::ReferenceType>(argType) &&
+          !fir::isPointerType(argType) &&
+          !func.getArgAttr(index, fir::getTargetAttrName()) &&
+          !func.getArgAttr(index, fir::getAsynchronousAttrName()) &&
+          !func.getArgAttr(index, fir::getVolatileAttrName()))
+        func.setArgAttr(index, nocapture, unitAttr);
+    }
+  }
+
   mlir::MLIRContext *context = &getContext();
   if (framePointerKind != mlir::LLVM::framePointerKind::FramePointerKind::None)
     func->setAttr("frame_pointer", mlir::LLVM::FramePointerKindAttr::get(
diff --git a/flang/test/Transforms/function-attrs.fir b/flang/test/Transforms/function-attrs.fir
new file mode 100644
index 00000000000000..54ee8d007692c0
--- /dev/null
+++ b/flang/test/Transforms/function-attrs.fir
@@ -0,0 +1,45 @@
+// RUN: fir-opt --function-attr %s | FileCheck %s
+
+// If a function has a body and is not bind(c), and if the dummy argument doesn't have the target,
+// asynchronous, volatile, or pointer attribute, then add llvm.nocapture to the dummy argument.
+
+func.func @_QParg_nocapture(%arg0: !fir.ref<i32> {fir.bindc_name = "tar", fir.target}, %arg1: !fir.ref<i32> {fir.asynchronous, fir.bindc_name = "asynch"}, %arg2: !fir.ref<i32> {fir.bindc_name = "vol", fir.volatile}, %arg3: !fir.ref<!fir.box<!fir.ptr<i32>>> {fir.bindc_name = "ptr"}, %arg4: !fir.ref<i32> {fir.bindc_name = "nocap"}) {
+    %0 = fir.dummy_scope : !fir.dscope
+    %1 = fir.declare %arg0 dummy_scope %0 {fortran_attrs = #fir.var_attrs<target>, uniq_name = "_QFarg_nocaptureEtar"} : (!fir.ref<i32>, !fir.dscope) -> !fir.ref<i32>
+    %2 = fir.declare %arg1 dummy_scope %0 {fortran_attrs = #fir.var_attrs<asynchronous>, uniq_name = "_QFarg_nocaptureEasynch"} : (!fir.ref<i32>, !fir.dscope) -> !fir.ref<i32>
+    %3 = fir.declare %arg2 dummy_scope %0 {uniq_name = "_QFarg_nocaptureEvol"} : (!fir.ref<i32>, !fir.dscope) -> !fir.ref<i32>
+    %4 = fir.declare %arg3 dummy_scope %0 {fortran_attrs = #fir.var_attrs<pointer>, uniq_name = "_QFarg_nocaptureEptr"} : (!fir.ref<!fir.box<!fir.ptr<i32>>>, !fir.dscope) -> !fir.ref<!fir.box<!fir.ptr<i32>>>
+    %5 = fir.declare %arg4 dummy_scope %0 {uniq_name = "_QFarg_nocaptureEnocap"} : (!fir.ref<i32>, !fir.dscope) -> !fir.ref<i32>
+    return
+}
+// CHECK-LABEL: func.func @_QParg_nocapture(
+// CHECK-SAME:                                 %[[ARG0:.*]]: !fir.ref<i32> {fir.bindc_name = "tar", fir.target},
+// CHECK-SAME:                                 %[[ARG1:.*]]: !fir.ref<i32> {fir.asynchronous, fir.bindc_name = "asynch"},
+// CHECK-SAME:                                 %[[ARG2:.*]]: !fir.ref<i32> {fir.bindc_name = "vol", fir.volatile},
+// CHECK-SAME:                                 %[[ARG3:.*]]: !fir.ref<!fir.box<!fir.ptr<i32>>> {fir.bindc_name = "ptr"},
+// CHECK-SAME:                                 %[[ARG4:.*]]: !fir.ref<i32> {fir.bindc_name = "nocap", llvm.nocapture}) {
+// CHECK:    return
+// CHECK-NEXT: }
+
+func.func @arg_nocapture_bindc(%arg0: !fir.ref<i32> {fir.bindc_name = "tar", fir.target}, %arg1: !fir.ref<i32> {fir.bindc_name = "nocap"}) attributes {fir.bindc_name = "arg_nocapture_bindc", fir.proc_attrs = #fir.proc_attrs<bind_c>} {
+    %0 = fir.dummy_scope : !fir.dscope
+    %1 = fir.declare %arg0 dummy_scope %0 {fortran_attrs = #fir.var_attrs<target>, uniq_name = "_QFarg_nocapture_bindcEtar"} : (!fir.ref<i32>, !fir.dscope) -> !fir.ref<i32>
+    %2 = fir.declare %arg1 dummy_scope %0 {uniq_name = "_QFarg_nocapture_bindcEnocap"} : (!fir.ref<i32>, !fir.dscope) -> !fir.ref<i32>
+    return
+}
+// CHECK-LABEL: func.func @arg_nocapture_bindc(
+// CHECK-NOT:  llvm.nocapture
+
+
+// If a function declaration is from a module and is not bind(c), and if the dummy argument doesn't have
+// the target, asynchronous, volatile, or pointer attribute, then add llvm.nocapture to the dummy argument.
+
+func.func private @_QMarg_modPcheck_args(!fir.ref<i32> {fir.target}, !fir.ref<i32> {fir.asynchronous}, !fir.ref<i32> {fir.volatile}, !fir.ref<!fir.box<!fir.ptr<i32>>>, !fir.ref<i32>, !fir.boxchar<1>, !fir.ref<complex<f32>>)
+// CHECK-LABEL: func.func private @_QMarg_modPcheck_args(
+// CHECK-SAME:                                 !fir.ref<i32> {fir.target},
+// CHECK-SAME:                                 !fir.ref<i32> {fir.asynchronous},
+// CHECK-SAME:                                 !fir.ref<i32> {fir.volatile},
+// CHECK-SAME:                                 !fir.ref<!fir.box<!fir.ptr<i32>>>,
+// CHECK-SAME:                                 !fir.ref<i32> {llvm.nocapture},
+// CHECK-SAME:                                 !fir.boxchar<1>,
+// CHECK-SAME:                                 !fir.ref<complex<f32>> {llvm.nocapture})

``````````

</details>


https://github.com/llvm/llvm-project/pull/116182