[Mlir-commits] [mlir] [mlir][analysis] Enhance the analysis precision of local alias analysis. (PR #95922)

[llvmlistbot at llvm.org]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-mlir

Author: donald chen (cxy-1993)

<details>
<summary>Changes</summary>

Local alias analysis utilizes view interfaces, branch interfaces, and region branch interfaces to identify underlying values. However, it overlooks operations like arith.select.

This patch enhances the underlying value identification process by introducing support for buffer view interfaces, leading to more accurate alias results.

---
Full diff: https://github.com/llvm/llvm-project/pull/95922.diff


2 Files Affected:

- (modified) mlir/lib/Analysis/AliasAnalysis/LocalAliasAnalysis.cpp (+21) 
- (modified) mlir/test/Analysis/test-alias-analysis.mlir (+18) 


``````````diff
diff --git a/mlir/lib/Analysis/AliasAnalysis/LocalAliasAnalysis.cpp b/mlir/lib/Analysis/AliasAnalysis/LocalAliasAnalysis.cpp
index b22f3fdc9fb7a..bc8990afacaee 100644
--- a/mlir/lib/Analysis/AliasAnalysis/LocalAliasAnalysis.cpp
+++ b/mlir/lib/Analysis/AliasAnalysis/LocalAliasAnalysis.cpp
@@ -9,6 +9,7 @@
 #include "mlir/Analysis/AliasAnalysis/LocalAliasAnalysis.h"
 
 #include "mlir/Analysis/AliasAnalysis.h"
+#include "mlir/Dialect/Bufferization/IR/BufferViewFlowOpInterface.h"
 #include "mlir/IR/Attributes.h"
 #include "mlir/IR/Block.h"
 #include "mlir/IR/Matchers.h"
@@ -131,6 +132,26 @@ static void collectUnderlyingAddressValues(OpResult result, unsigned maxDepth,
   if (ViewLikeOpInterface view = dyn_cast<ViewLikeOpInterface>(op))
     return collectUnderlyingAddressValues(view.getViewSource(), maxDepth,
                                           visited, output);
+
+  // If this is a buffer view, unwarp to the operands viewed from.
+  if (mlir::bufferization::BufferViewFlowOpInterface bufferView =
+          dyn_cast<mlir::bufferization::BufferViewFlowOpInterface>(op)) {
+    SmallVector<Value> viewSources;
+    bufferView.populateDependencies(
+        [&](ValueRange operands, ValueRange results) {
+          if (results.size() == 1 && results[0] == result) {
+            viewSources.append(operands.begin(), operands.end());
+          }
+        });
+
+    if (!viewSources.empty()) {
+      for (Value viewSource : viewSources) {
+        collectUnderlyingAddressValues(viewSource, maxDepth, visited, output);
+      }
+      return;
+    }
+  }
+
   // Check to see if we can reason about the control flow of this op.
   if (auto branch = dyn_cast<RegionBranchOpInterface>(op)) {
     return collectUnderlyingAddressValues(branch, /*region=*/nullptr, result,
diff --git a/mlir/test/Analysis/test-alias-analysis.mlir b/mlir/test/Analysis/test-alias-analysis.mlir
index 8cbee61c78b45..459ede3bdcb53 100644
--- a/mlir/test/Analysis/test-alias-analysis.mlir
+++ b/mlir/test/Analysis/test-alias-analysis.mlir
@@ -256,3 +256,21 @@ func.func @constants(%arg: memref<2xf32>) attributes {test.ptr = "func"} {
 
   return
 }
+
+// -----
+
+// CHECK-LABEL: Testing : "buffer_view"
+// CHECK-DAG: alloc_1#0 <-> select#0: NoAlias
+// CHECK-DAG: alloca_2#0 <-> select#0: MayAlias
+// CHECK-DAG: alloca_3#0 <-> select#0: MayAlias
+// CHECK-DAG: select#0 <-> func.region0#0: NoAlias
+// CHECK-DAG: select#0 <-> func.region0#1: NoAlias
+// CHECK-DAG: select#0 <-> func.region0#2: NoAlias
+func.func @buffer_view(%arg: memref<2xf32>, %size: index, %cond : i1) attributes {test.ptr = "func"} {
+  %1 = memref.alloc() {test.ptr = "alloc_1"} : memref<8x64xf32>
+  %c0 = arith.constant 0 : index
+  %2 = memref.alloca (%size) {test.ptr = "alloca_2"} : memref<?xi8>
+  %3 = memref.alloca (%size) {test.ptr = "alloca_3"} : memref<?xi8>
+  %4 = arith.select %cond, %2, %3 {test.ptr = "select"}: memref<?xi8>
+  return
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/95922