[flang-commits] [flang] [flang] Added fir.dummy_scope operation to preserve dummy arguments association. (PR #90642)

Slava Zakharin via flang-commits flang-commits at lists.llvm.org
Tue Apr 30 11:11:26 PDT 2024


https://github.com/vzakhari updated https://github.com/llvm/llvm-project/pull/90642

>From 4432577b44a98d489cbfb53e29331c8be5d63994 Mon Sep 17 00:00:00 2001
From: Slava Zakharin <szakharin at nvidia.com>
Date: Tue, 30 Apr 2024 09:55:50 -0700
Subject: [PATCH 1/3] [flang] Added fir.dummy_scope operation to preserve dummy
 arguments association.

The new operation is just an abstract attribute that is attached to
[hl]fir.declare operations of dummy arguments of a subroutine.
Dummy arguments of the same subroutine refer to the same fir.dummy_scope,
so they can be recognized as such during FIR AliasAnalysis.
Note that the fir.dummy_scope must be specific to the runtime instantiation
of a subroutine, so any MLIR inlining/cloning should duplicate and unique it
vs using the same fir.dummy_scope for different runtime instantiations.
This is why I made it an operation rather than an attribute.
The new operation uses a write effect on DebuggingResource, same as
[hl]fir.declare, to avoid optimizing it away.
---
 .../include/flang/Optimizer/Dialect/FIROps.td | 84 ++++++++++++++++++-
 .../include/flang/Optimizer/HLFIR/HLFIROps.td |  4 +-
 flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp     |  3 +-
 .../HLFIR/Transforms/ConvertToFIR.cpp         |  4 +-
 flang/test/Fir/dummy_scope.fir                | 34 ++++++++
 flang/test/HLFIR/dummy_scope.fir              | 34 ++++++++
 .../Optimizer/FortranVariableTest.cpp         |  9 +-
 7 files changed, 163 insertions(+), 9 deletions(-)
 create mode 100644 flang/test/Fir/dummy_scope.fir
 create mode 100644 flang/test/HLFIR/dummy_scope.fir

diff --git a/flang/include/flang/Optimizer/Dialect/FIROps.td b/flang/include/flang/Optimizer/Dialect/FIROps.td
index 496193e25cab61..95cce67137890f 100644
--- a/flang/include/flang/Optimizer/Dialect/FIROps.td
+++ b/flang/include/flang/Optimizer/Dialect/FIROps.td
@@ -3074,6 +3074,7 @@ def fir_DeclareOp : fir_Op<"declare", [AttrSizedOperandSegments,
     AnyRefOrBox:$memref,
     Optional<AnyShapeOrShiftType>:$shape,
     Variadic<AnyIntegerType>:$typeparams,
+    Optional<I1>:$dummy_scope,
     Builtin_StringAttr:$uniq_name,
     OptionalAttr<fir_FortranVariableFlagsAttr>:$fortran_attrs,
     OptionalAttr<fir_CUDADataAttributeAttr>:$cuda_attr
@@ -3083,7 +3084,8 @@ def fir_DeclareOp : fir_Op<"declare", [AttrSizedOperandSegments,
 
   let assemblyFormat = [{
     $memref (`(` $shape^ `)`)? (`typeparams` $typeparams^)?
-     attr-dict `:` functional-type(operands, results)
+    (`dummy_scope` $dummy_scope^)?
+    attr-dict `:` functional-type(operands, results)
   }];
 
   let hasVerifier = 1;
@@ -3247,4 +3249,84 @@ def fir_CUDADeallocateOp : fir_Op<"cuda_deallocate",
   let hasVerifier = 1;
 }
 
+def fir_DummyScopeOp : fir_Op<"dummy_scope",
+    [MemoryEffects<[MemWrite<DebuggingResource>]>]> {
+  let summary = "Define a scope for dummy arguments";
+
+  let description = [{
+    An abstract handle to be used to associate dummy arguments of the same
+    subroutine between each other. By lowering, all [hl]fir.declare
+    operations representing declarations of dummy arguments of a subroutine
+    use the result of this operation. This allows recognizing the references
+    of these dummy arguments as belonging to the same runtime instance
+    of the subroutine even after MLIR inlining. Thus, the Fortran aliasing
+    rules might be applied to those references based on the original
+    declarations of the dummy arguments.
+    For example:
+    ```
+      subroutine test(x, y)
+        real, target :: x, y
+        x = y ! may alias
+        call inner(x, y)
+      contains
+        subroutine inner(x, y)
+          real :: x, y
+          x = y ! may not alias
+        end subroutine inner
+      end subroutine test
+    ```
+    After MLIR inlining this may look like this:
+    ```
+      func.func @_QPtest(
+          %arg0: !fir.ref<f32> {fir.target},
+          %arg1: !fir.ref<f32> {fir.target}) {
+        %0 = fir.declare %arg0 {fortran_attrs = #fir.var_attrs<target>} :
+            (!fir.ref<f32>) -> !fir.ref<f32>
+        %1 = fir.declare %arg1 {fortran_attrs = #fir.var_attrs<target>} :
+            (!fir.ref<f32>) -> !fir.ref<f32>
+        %2 = fir.load %1 : !fir.ref<f32>
+        fir.store %2 to %0 : !fir.ref<f32>
+        %3 = fir.declare %0 : (!fir.ref<f32>) -> !fir.ref<f32>
+        %4 = fir.declare %1 : (!fir.ref<f32>) -> !fir.ref<f32>
+        %5 = fir.load %4 : !fir.ref<f32>
+        fir.store %5 to %3 : !fir.ref<f32>
+        return
+      }
+    ```
+    Without marking %3 and %4 as declaring the dummy arguments
+    of the same runtime instance of `inner` subroutine the FIR
+    AliasAnalysis cannot deduce non-aliasing for the second load/store pair.
+    This information may be preserved by using fir.dummy_scope operation:
+    ```
+      func.func @_QPtest(
+          %arg0: !fir.ref<f32> {fir.target},
+          %arg1: !fir.ref<f32> {fir.target}) {
+        %h1 = fir.dummy_scope : i1
+        %0 = fir.declare %arg0 dummy_scope(%h1)
+            {fortran_attrs = #fir.var_attrs<target>} :
+            (!fir.ref<f32>) -> !fir.ref<f32>
+        %1 = fir.declare %arg1 dummy_scope(%h1)
+            {fortran_attrs = #fir.var_attrs<target>} :
+            (!fir.ref<f32>) -> !fir.ref<f32>
+        %2 = fir.load %1 : !fir.ref<f32>
+        fir.store %2 to %0 : !fir.ref<f32>
+        %h2 = fir.dummy_scope : i1
+        %3 = fir.declare %0 dummy_scope(%h2) : (!fir.ref<f32>) -> !fir.ref<f32>
+        %4 = fir.declare %1 dummy_scope(%h2) : (!fir.ref<f32>) -> !fir.ref<f32>
+        %5 = fir.load %4 : !fir.ref<f32>
+        fir.store %5 to %3 : !fir.ref<f32>
+        return
+      }
+    ```
+    Note that even if `inner` is called and inlined twice inside
+    `test`, the two inlined instances of `inner` must use two different
+    fir.dummy_scope operations for their fir.declare ops. This
+    two distinct fir.dummy_scope must remain distinct during the optimizations.
+    This is guaranteed by the write memory effect on the DebuggingResource.
+  }];
+
+  let results = (outs I1);
+  let assemblyFormat = "attr-dict `:` type(results)";
+}
+
 #endif
diff --git a/flang/include/flang/Optimizer/HLFIR/HLFIROps.td b/flang/include/flang/Optimizer/HLFIR/HLFIROps.td
index 743a6c98ec1a03..be0bb770a3e171 100644
--- a/flang/include/flang/Optimizer/HLFIR/HLFIROps.td
+++ b/flang/include/flang/Optimizer/HLFIR/HLFIROps.td
@@ -87,6 +87,7 @@ def hlfir_DeclareOp : hlfir_Op<"declare", [AttrSizedOperandSegments,
     AnyRefOrBox:$memref,
     Optional<AnyShapeOrShiftType>:$shape,
     Variadic<AnyIntegerType>:$typeparams,
+    Optional<I1>:$dummy_scope,
     Builtin_StringAttr:$uniq_name,
     OptionalAttr<fir_FortranVariableFlagsAttr>:$fortran_attrs,
     OptionalAttr<fir_CUDADataAttributeAttr>:$cuda_attr
@@ -96,7 +97,8 @@ def hlfir_DeclareOp : hlfir_Op<"declare", [AttrSizedOperandSegments,
 
   let assemblyFormat = [{
     $memref (`(` $shape^ `)`)? (`typeparams` $typeparams^)?
-     attr-dict `:` functional-type(operands, results)
+    (`dummy_scope` $dummy_scope^)?
+    attr-dict `:` functional-type(operands, results)
   }];
 
   let builders = [
diff --git a/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp b/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp
index 0d62ca4954e6bf..4b586ad1d3a4af 100644
--- a/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp
+++ b/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp
@@ -133,7 +133,8 @@ void hlfir::DeclareOp::build(mlir::OpBuilder &builder,
   mlir::Type hlfirVariableType =
       getHLFIRVariableType(inputType, hasExplicitLbs);
   build(builder, result, {hlfirVariableType, inputType}, memref, shape,
-        typeparams, nameAttr, fortran_attrs, cuda_attr);
+        typeparams, /*dummy_scope=*/nullptr, nameAttr, fortran_attrs,
+        cuda_attr);
 }
 
 mlir::LogicalResult hlfir::DeclareOp::verify() {
diff --git a/flang/lib/Optimizer/HLFIR/Transforms/ConvertToFIR.cpp b/flang/lib/Optimizer/HLFIR/Transforms/ConvertToFIR.cpp
index 517285dce133de..08869bcd00e42f 100644
--- a/flang/lib/Optimizer/HLFIR/Transforms/ConvertToFIR.cpp
+++ b/flang/lib/Optimizer/HLFIR/Transforms/ConvertToFIR.cpp
@@ -328,8 +328,8 @@ class DeclareOpConversion : public mlir::OpRewritePattern<hlfir::DeclareOp> {
       cudaAttr = fir::CUDADataAttributeAttr::get(rewriter.getContext(), *attr);
     auto firDeclareOp = rewriter.create<fir::DeclareOp>(
         loc, memref.getType(), memref, declareOp.getShape(),
-        declareOp.getTypeparams(), declareOp.getUniqName(), fortranAttrs,
-        cudaAttr);
+        declareOp.getTypeparams(), /*dummy_scope=*/nullptr,
+        declareOp.getUniqName(), fortranAttrs, cudaAttr);
 
     // Propagate other attributes from hlfir.declare to fir.declare.
     // OpenACC's acc.declare is one example. Right now, the propagation
diff --git a/flang/test/Fir/dummy_scope.fir b/flang/test/Fir/dummy_scope.fir
new file mode 100644
index 00000000000000..8def2759fb77d6
--- /dev/null
+++ b/flang/test/Fir/dummy_scope.fir
@@ -0,0 +1,34 @@
+// RUN: fir-opt %s | fir-opt | FileCheck %s
+// RUN: fir-opt %s | fir-opt -cse | FileCheck %s
+
+// CHECK-LABEL:   func.func @dummy_scope(
+// CHECK-SAME:                           %[[VAL_0:.*]]: !fir.ref<f32>) {
+// CHECK:           %[[VAL_1:.*]] = fir.dummy_scope : i1
+// CHECK:           %[[VAL_2:.*]] = fir.declare %[[VAL_0]] dummy_scope %[[VAL_1]] {uniq_name = "x"} : (!fir.ref<f32>, i1) -> !fir.ref<f32>
+// CHECK:           return
+// CHECK:         }
+func.func @dummy_scope(%arg0: !fir.ref<f32>) {
+  %scope = fir.dummy_scope : i1
+  %0 = fir.declare %arg0 dummy_scope %scope {uniq_name = "x"} : (!fir.ref<f32>, i1) -> !fir.ref<f32>
+  return
+}
+
+// CHECK-LABEL:   func.func @dummy_scopes(
+// CHECK-SAME:                            %[[VAL_0:.*]]: !fir.ref<f32>) {
+// CHECK:           %[[VAL_1:.*]] = fir.dummy_scope : i1
+// CHECK:           %[[VAL_2:.*]] = fir.declare %[[VAL_0]] dummy_scope %[[VAL_1]] {uniq_name = "x"} : (!fir.ref<f32>, i1) -> !fir.ref<f32>
+// CHECK:           %[[VAL_3:.*]] = fir.dummy_scope : i1
+// CHECK:           %[[VAL_4:.*]] = fir.declare %[[VAL_0]] dummy_scope %[[VAL_3]] {uniq_name = "innerEx"} : (!fir.ref<f32>, i1) -> !fir.ref<f32>
+// CHECK:           %[[VAL_5:.*]] = fir.dummy_scope : i1
+// CHECK:           %[[VAL_6:.*]] = fir.declare %[[VAL_0]] dummy_scope %[[VAL_5]] {uniq_name = "innerEx"} : (!fir.ref<f32>, i1) -> !fir.ref<f32>
+// CHECK:           return
+// CHECK:         }
+func.func @dummy_scopes(%arg0: !fir.ref<f32>) {
+  %scope_out = fir.dummy_scope : i1
+  %0 = fir.declare %arg0 dummy_scope %scope_out {uniq_name = "x"} : (!fir.ref<f32>, i1) -> !fir.ref<f32>
+  %scope_in1 = fir.dummy_scope : i1
+  %1 = fir.declare %arg0 dummy_scope %scope_in1 {uniq_name = "innerEx"} : (!fir.ref<f32>, i1) -> !fir.ref<f32>
+  %scope_in2 = fir.dummy_scope : i1
+  %2 = fir.declare %arg0 dummy_scope %scope_in2 {uniq_name = "innerEx"} : (!fir.ref<f32>, i1) -> !fir.ref<f32>
+  return
+}
diff --git a/flang/test/HLFIR/dummy_scope.fir b/flang/test/HLFIR/dummy_scope.fir
new file mode 100644
index 00000000000000..304ebccfbe3197
--- /dev/null
+++ b/flang/test/HLFIR/dummy_scope.fir
@@ -0,0 +1,34 @@
+// RUN: fir-opt %s | fir-opt | FileCheck %s
+// RUN: fir-opt %s | fir-opt -cse | FileCheck %s
+
+// CHECK-LABEL:   func.func @dummy_scope(
+// CHECK-SAME:                           %[[VAL_0:.*]]: !fir.ref<f32>) {
+// CHECK:           %[[VAL_1:.*]] = fir.dummy_scope : i1
+// CHECK:           %[[VAL_2:.*]]:2 = hlfir.declare %[[VAL_0]] dummy_scope %[[VAL_1]] {uniq_name = "x"} : (!fir.ref<f32>, i1) -> (!fir.ref<f32>, !fir.ref<f32>)
+// CHECK:           return
+// CHECK:         }
+func.func @dummy_scope(%arg0: !fir.ref<f32>) {
+  %scope = fir.dummy_scope : i1
+  %0:2 = hlfir.declare %arg0 dummy_scope %scope {uniq_name = "x"} : (!fir.ref<f32>, i1) -> (!fir.ref<f32>, !fir.ref<f32>)
+  return
+}
+
+// CHECK-LABEL:   func.func @dummy_scopes(
+// CHECK-SAME:                            %[[VAL_0:.*]]: !fir.ref<f32>) {
+// CHECK:           %[[VAL_1:.*]] = fir.dummy_scope : i1
+// CHECK:           %[[VAL_2:.*]]:2 = hlfir.declare %[[VAL_0]] dummy_scope %[[VAL_1]] {uniq_name = "x"} : (!fir.ref<f32>, i1) -> (!fir.ref<f32>, !fir.ref<f32>)
+// CHECK:           %[[VAL_3:.*]] = fir.dummy_scope : i1
+// CHECK:           %[[VAL_4:.*]]:2 = hlfir.declare %[[VAL_0]] dummy_scope %[[VAL_3]] {uniq_name = "innerEx"} : (!fir.ref<f32>, i1) -> (!fir.ref<f32>, !fir.ref<f32>)
+// CHECK:           %[[VAL_5:.*]] = fir.dummy_scope : i1
+// CHECK:           %[[VAL_6:.*]]:2 = hlfir.declare %[[VAL_0]] dummy_scope %[[VAL_5]] {uniq_name = "innerEx"} : (!fir.ref<f32>, i1) -> (!fir.ref<f32>, !fir.ref<f32>)
+// CHECK:           return
+// CHECK:         }
+func.func @dummy_scopes(%arg0: !fir.ref<f32>) {
+  %scope_out = fir.dummy_scope : i1
+  %0:2 = hlfir.declare %arg0 dummy_scope %scope_out {uniq_name = "x"} : (!fir.ref<f32>, i1) -> (!fir.ref<f32>, !fir.ref<f32>)
+  %scope_in1 = fir.dummy_scope : i1
+  %1:2 = hlfir.declare %arg0 dummy_scope %scope_in1 {uniq_name = "innerEx"} : (!fir.ref<f32>, i1) -> (!fir.ref<f32>, !fir.ref<f32>)
+  %scope_in2 = fir.dummy_scope : i1
+  %2:2 = hlfir.declare %arg0 dummy_scope %scope_in2 {uniq_name = "innerEx"} : (!fir.ref<f32>, i1) -> (!fir.ref<f32>, !fir.ref<f32>)
+  return
+}
diff --git a/flang/unittests/Optimizer/FortranVariableTest.cpp b/flang/unittests/Optimizer/FortranVariableTest.cpp
index 790f735a6cf29e..f5f559ef887c85 100644
--- a/flang/unittests/Optimizer/FortranVariableTest.cpp
+++ b/flang/unittests/Optimizer/FortranVariableTest.cpp
@@ -48,7 +48,8 @@ TEST_F(FortranVariableTest, SimpleScalar) {
   mlir::Value addr = builder->create<fir::AllocaOp>(loc, eleType);
   auto name = mlir::StringAttr::get(&context, "x");
   auto declare = builder->create<fir::DeclareOp>(loc, addr.getType(), addr,
-      /*shape=*/mlir::Value{}, /*typeParams=*/std::nullopt, name,
+      /*shape=*/mlir::Value{}, /*typeParams=*/std::nullopt,
+      /*dummy_scope=*/nullptr, name,
       /*fortran_attrs=*/fir::FortranVariableFlagsAttr{},
       /*cuda_attr=*/fir::CUDADataAttributeAttr{});
 
@@ -74,7 +75,7 @@ TEST_F(FortranVariableTest, CharacterScalar) {
       loc, eleType, /*pinned=*/false, typeParams);
   auto name = mlir::StringAttr::get(&context, "x");
   auto declare = builder->create<fir::DeclareOp>(loc, addr.getType(), addr,
-      /*shape=*/mlir::Value{}, typeParams, name,
+      /*shape=*/mlir::Value{}, typeParams, /*dummy_scope=*/nullptr, name,
       /*fortran_attrs=*/fir::FortranVariableFlagsAttr{},
       /*cuda_attr=*/fir::CUDADataAttributeAttr{});
 
@@ -105,7 +106,7 @@ TEST_F(FortranVariableTest, SimpleArray) {
   mlir::Value shape = createShape(extents);
   auto name = mlir::StringAttr::get(&context, "x");
   auto declare = builder->create<fir::DeclareOp>(loc, addr.getType(), addr,
-      shape, /*typeParams*/ std::nullopt, name,
+      shape, /*typeParams*/ std::nullopt, /*dummy_scope=*/nullptr, name,
       /*fortran_attrs=*/fir::FortranVariableFlagsAttr{},
       /*cuda_attr=*/fir::CUDADataAttributeAttr{});
 
@@ -136,7 +137,7 @@ TEST_F(FortranVariableTest, CharacterArray) {
   mlir::Value shape = createShape(extents);
   auto name = mlir::StringAttr::get(&context, "x");
   auto declare = builder->create<fir::DeclareOp>(loc, addr.getType(), addr,
-      shape, typeParams, name,
+      shape, typeParams, /*dummy_scope=*/nullptr, name,
       /*fortran_attrs=*/fir::FortranVariableFlagsAttr{},
       /*cuda_attr=*/fir::CUDADataAttributeAttr{});
 

>From 33d03b4af57e25e7cf298d2d1513ce929de0a1a3 Mon Sep 17 00:00:00 2001
From: Slava Zakharin <szakharin at nvidia.com>
Date: Tue, 30 Apr 2024 09:56:00 -0700
Subject: [PATCH 2/3] [flang] Conversion of dummy_scope operand of
 hlfir.declare to fir.declare.

---
 flang/lib/Optimizer/HLFIR/Transforms/ConvertToFIR.cpp |  2 +-
 flang/test/HLFIR/declare-codegen.fir                  | 10 ++++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/flang/lib/Optimizer/HLFIR/Transforms/ConvertToFIR.cpp b/flang/lib/Optimizer/HLFIR/Transforms/ConvertToFIR.cpp
index 08869bcd00e42f..3570e0011ca7e6 100644
--- a/flang/lib/Optimizer/HLFIR/Transforms/ConvertToFIR.cpp
+++ b/flang/lib/Optimizer/HLFIR/Transforms/ConvertToFIR.cpp
@@ -328,7 +328,7 @@ class DeclareOpConversion : public mlir::OpRewritePattern<hlfir::DeclareOp> {
       cudaAttr = fir::CUDADataAttributeAttr::get(rewriter.getContext(), *attr);
     auto firDeclareOp = rewriter.create<fir::DeclareOp>(
         loc, memref.getType(), memref, declareOp.getShape(),
-        declareOp.getTypeparams(), /*dummy_scope=*/nullptr,
+        declareOp.getTypeparams(), declareOp.getDummyScope(),
         declareOp.getUniqName(), fortranAttrs, cudaAttr);
 
     // Propagate other attributes from hlfir.declare to fir.declare.
diff --git a/flang/test/HLFIR/declare-codegen.fir b/flang/test/HLFIR/declare-codegen.fir
index 3e80a52be45248..d079aa776a3a9c 100644
--- a/flang/test/HLFIR/declare-codegen.fir
+++ b/flang/test/HLFIR/declare-codegen.fir
@@ -200,3 +200,13 @@ func.func @test_optional_declare(%arg0: !fir.box<!fir.array<?xi32>>) {
 // CHECK:    %[[VAL_7:.*]] = fir.absent !fir.box<!fir.array<?xi32>>
 // CHECK:    fir.result %[[VAL_7]] : !fir.box<!fir.array<?xi32>>
 // CHECK:  }
+
+func.func @dummy_scope(%arg0: !fir.ref<f32>) {
+  %scope = fir.dummy_scope : i1
+  %0:2 = hlfir.declare %arg0 dummy_scope %scope {uniq_name = "x"} : (!fir.ref<f32>, i1) -> (!fir.ref<f32>, !fir.ref<f32>)
+  return
+}
+// CHECK-LABEL:   func.func @dummy_scope(
+// CHECK-SAME:    %[[VAL_0:.*]]: !fir.ref<f32>) {
+// CHECK:         %[[SCOPE:.*]] = fir.dummy_scope : i1
+// CHECK:         %[[VAL_1:.*]] = fir.declare %[[VAL_0]] dummy_scope %[[SCOPE]] {uniq_name = "x"} : (!fir.ref<f32>, i1) -> !fir.ref<f32>

>From efba91f7a6f1ffce22d15277c7f586b8f03c2b00 Mon Sep 17 00:00:00 2001
From: Slava Zakharin <szakharin at nvidia.com>
Date: Tue, 30 Apr 2024 09:56:04 -0700
Subject: [PATCH 3/3] [flang] PreCGRewrite for fir.dummy_scope.

---
 flang/lib/Optimizer/CodeGen/PreCGRewrite.cpp | 18 +++++++++++++++++-
 flang/test/Fir/dummy-scope-codegen.fir       |  9 +++++++++
 2 files changed, 26 insertions(+), 1 deletion(-)
 create mode 100644 flang/test/Fir/dummy-scope-codegen.fir

diff --git a/flang/lib/Optimizer/CodeGen/PreCGRewrite.cpp b/flang/lib/Optimizer/CodeGen/PreCGRewrite.cpp
index ce7ee22d5d7744..5bd3ec8d18450e 100644
--- a/flang/lib/Optimizer/CodeGen/PreCGRewrite.cpp
+++ b/flang/lib/Optimizer/CodeGen/PreCGRewrite.cpp
@@ -281,6 +281,20 @@ class DeclareOpConversion : public mlir::OpRewritePattern<fir::DeclareOp> {
   }
 };
 
+class DummyScopeOpConversion
+    : public mlir::OpRewritePattern<fir::DummyScopeOp> {
+public:
+  using OpRewritePattern::OpRewritePattern;
+
+  mlir::LogicalResult
+  matchAndRewrite(fir::DummyScopeOp dummyScopeOp,
+                  mlir::PatternRewriter &rewriter) const override {
+    rewriter.replaceOpWithNewOp<fir::UndefOp>(dummyScopeOp,
+                                              dummyScopeOp.getType());
+    return mlir::success();
+  }
+};
+
 class CodeGenRewrite : public fir::impl::CodeGenRewriteBase<CodeGenRewrite> {
 public:
   void runOnOperation() override final {
@@ -293,6 +307,7 @@ class CodeGenRewrite : public fir::impl::CodeGenRewriteBase<CodeGenRewrite> {
     target.addIllegalOp<fir::ArrayCoorOp>();
     target.addIllegalOp<fir::ReboxOp>();
     target.addIllegalOp<fir::DeclareOp>();
+    target.addIllegalOp<fir::DummyScopeOp>();
     target.addDynamicallyLegalOp<fir::EmboxOp>([](fir::EmboxOp embox) {
       return !(embox.getShape() ||
                mlir::isa<fir::SequenceType>(
@@ -321,5 +336,6 @@ std::unique_ptr<mlir::Pass> fir::createFirCodeGenRewritePass() {
 
 void fir::populatePreCGRewritePatterns(mlir::RewritePatternSet &patterns) {
   patterns.insert<EmboxConversion, ArrayCoorConversion, ReboxConversion,
-                  DeclareOpConversion>(patterns.getContext());
+                  DeclareOpConversion, DummyScopeOpConversion>(
+      patterns.getContext());
 }
diff --git a/flang/test/Fir/dummy-scope-codegen.fir b/flang/test/Fir/dummy-scope-codegen.fir
new file mode 100644
index 00000000000000..d8bdd0a822a5f0
--- /dev/null
+++ b/flang/test/Fir/dummy-scope-codegen.fir
@@ -0,0 +1,9 @@
+// RUN: fir-opt --cg-rewrite %s -o - | FileCheck %s
+
+func.func @dummy_scope(%arg0: !fir.ref<f32>) {
+  %scope = fir.dummy_scope : i1
+  %0 = fir.declare %arg0 dummy_scope %scope {uniq_name = "x"} : (!fir.ref<f32>, i1) -> !fir.ref<f32>
+  return
+}
+// CHECK-LABEL: func.func @dummy_scope(
+// CHECK-NEXT: return



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