[mlir] Add bufferization option for parallel region check (llvm#94645)

Handling parallel region RaW conflicts should usually be the
responsibility of the source program, rather than bufferization
analysis. However, to preserve current functionality, checks on parallel
regions is put behind a bufferization in this PR, which is on by
default. Default functionality will not change, but this PR enables the
option to leave parallelism checks out of the bufferization analysis.

Author: Max191

mlir/include/mlir/Dialect/Bufferization/IR/BufferizableOpInterface.h

@@ -309,6 +309,11 @@ struct BufferizationOptions {
   /// bufferized or not.
   bool bufferizeFunctionBoundaries = false;
 
+  // Specifies whether to account for parallel regions in RaW analysis. If true,
+  // then writes inside of parallel regions that write to buffers defined
+  // outside of the parallel region will be given a new buffer.
+  bool checkParallelRegions = true;
+
   /// Certain ops have aliasing OpOperand/OpResult invariants (e.g., scf.for).
   /// If this flag is set to `false`, those invariants are no longer enforced
   /// with buffer copies.

mlir/include/mlir/Dialect/Bufferization/TransformOps/BufferizationTransformOps.td

@@ -88,6 +88,7 @@ def OneShotBufferizeOp
       DefaultValuedAttr<BoolAttr, "false">:$dump_alias_sets,
       DefaultValuedAttr<BoolAttr, "false">:$test_analysis_only,
       DefaultValuedAttr<BoolAttr, "false">:$print_conflicts,
+      DefaultValuedAttr<BoolAttr, "true">:$check_parallel_regions,
       DefaultValuedAttr<StrAttr, "\"memref.copy\"">:$memcpy_op);
 
   let results = (outs TransformHandleTypeInterface:$transformed);

mlir/include/mlir/Dialect/Bufferization/Transforms/Passes.td

@@ -498,6 +498,8 @@ def OneShotBufferize : Pass<"one-shot-bufferize", "ModuleOp"> {
     Option<"bufferizeFunctionBoundaries", "bufferize-function-boundaries",
            "bool", /*default=*/"0",
            "Bufferize function boundaries (experimental).">,
+    Option<"checkParallelRegions", "check-parallel-regions", "bool",
+           /*default=*/"true", "Account for parallel regions in RaW analysis.">,
     Option<"copyBeforeWrite", "copy-before-write", "bool", /*default=*/"false",
            "Skip the analysis. Make a buffer copy on every write.">,
     ListOption<"dialectFilter", "dialect-filter", "std::string",

mlir/lib/Dialect/Bufferization/Transforms/Bufferize.cpp

@@ -226,6 +226,7 @@ struct OneShotBufferizePass
       opt.printConflicts = printConflicts;
       opt.testAnalysisOnly = testAnalysisOnly;
       opt.bufferizeFunctionBoundaries = bufferizeFunctionBoundaries;
+      opt.checkParallelRegions = checkParallelRegions;
       opt.noAnalysisFuncFilter = noAnalysisFuncFilter;
 
       // Configure type converter.

mlir/lib/Dialect/Bufferization/Transforms/OneShotAnalysis.cpp

@@ -611,7 +611,7 @@ hasReadAfterWriteInterference(const DenseSet<OpOperand *> &usesRead,
   // Before going through the main RaW analysis, find cases where a buffer must
   // be privatized due to parallelism. If the result of a write is never read,
   // privatization is not necessary (and large parts of the IR are likely dead).
-  if (!usesRead.empty()) {
+  if (options.checkParallelRegions && !usesRead.empty()) {
     for (OpOperand *uConflictingWrite : usesWrite) {
       // Find the allocation point or last write (definition) of the buffer.
       // Note: In contrast to `findDefinitions`, this also returns results of

mlir/test/Dialect/SCF/one-shot-bufferize-analysis.mlir

@@ -1,4 +1,5 @@
-// RUN: mlir-opt %s -one-shot-bufferize="allow-return-allocs-from-loops bufferize-function-boundaries test-analysis-only" -split-input-file | FileCheck %s
+// RUN: mlir-opt %s -one-shot-bufferize="allow-return-allocs-from-loops bufferize-function-boundaries test-analysis-only" -split-input-file | FileCheck %s --check-prefixes=CHECK,PARALLEL-CHECK
+// RUN: mlir-opt %s -one-shot-bufferize="allow-return-allocs-from-loops bufferize-function-boundaries test-analysis-only check-parallel-regions=false" -split-input-file | FileCheck %s --check-prefixes=CHECK,NO-PARALLEL-CHECK
 
 // Run fuzzer with different seeds.
 // RUN: mlir-opt %s -one-shot-bufferize="allow-return-allocs-from-loops bufferize-function-boundaries test-analysis-only analysis-heuristic=fuzzer analysis-fuzzer-seed=23" -split-input-file -o /dev/null
@@ -811,8 +812,10 @@ func.func @parallel_region() -> tensor<320xf32>
   %0 = scf.forall (%arg0) in (%c320) shared_outs(%arg1 = %alloc0) -> (tensor<320xf32>) {
     %val = "test.foo"() : () -> (f32)
     // linalg.fill must bufferize out-of-place because every thread needs a
-    // private copy of %alloc1.
-    // CHECK: linalg.fill {__inplace_operands_attr__ = ["none", "false"]}
+    // private copy of %alloc1. If not accounting for parallel regions, the fill
+    // can bufferize in place.
+    // PARALLEL-CHECK:    linalg.fill {__inplace_operands_attr__ = ["none", "false"]}
+    // NO-PARALLEL-CHECK: linalg.fill {__inplace_operands_attr__ = ["none", "true"]}
     %fill = linalg.fill ins(%val : f32) outs(%alloc1 : tensor<1xf32>) -> tensor<1xf32>
     scf.forall.in_parallel {
       // CHECK: tensor.parallel_insert_slice {{.*}} {__inplace_operands_attr__ = ["true", "true", "none"]}
@@ -841,8 +844,10 @@ func.func @parallel_region_mixed_def(%c: i1) -> tensor<320xf32>
     }
     %val = "test.foo"() : () -> (f32)
     // linalg.fill must bufferize out-of-place because every thread needs a
-    // private copy of %alloc1.
-    // CHECK: linalg.fill {__inplace_operands_attr__ = ["none", "false"]}
+    // private copy of %alloc1. If not accounting for parallel regions, the fill
+    // can bufferize in place.
+    // PARALLEL-CHECK: linalg.fill {__inplace_operands_attr__ = ["none", "false"]}
+    // NO-PARALLEL-CHECK: linalg.fill {__inplace_operands_attr__ = ["none", "true"]}
     %fill = linalg.fill ins(%val : f32) outs(%selected : tensor<1xf32>) -> tensor<1xf32>
     scf.forall.in_parallel {
       // CHECK: tensor.parallel_insert_slice {{.*}} {__inplace_operands_attr__ = ["true", "true", "none"]}
@@ -866,8 +871,10 @@ func.func @parallel_region_two_writes(%f: f32) -> tensor<320xf32>
   %0 = scf.forall (%arg0) in (%c320) shared_outs(%arg1 = %alloc0) -> (tensor<320xf32>) {
     %val = "test.foo"() : () -> (f32)
     // linalg.fill must bufferize out-of-place because every thread needs a
-    // private copy of %alloc1.
-    // CHECK: linalg.fill {__inplace_operands_attr__ = ["none", "false"]}
+    // private copy of %alloc1. If not accounting for parallel regions, the fill
+    // can bufferize in place.
+    // PARALLEL-CHECK: linalg.fill {__inplace_operands_attr__ = ["none", "false"]}
+    // NO-PARALLEL-CHECK: linalg.fill {__inplace_operands_attr__ = ["none", "true"]}
     %fill = linalg.fill ins(%val : f32) outs(%alloc1 : tensor<1xf32>) -> tensor<1xf32>
     // CHECK: tensor.insert
     // CHECK-SAME: __inplace_operands_attr__ = ["none", "true", "none"]