[Mlir-commits] [mlir] [MLIR][Affine] Check dependences during MDG init (PR #156422)

[Arnab Dutta]

================
@@ -241,7 +242,96 @@ addNodeToMDG(Operation *nodeOp, MemRefDependenceGraph &mdg,
   return &node;
 }
 
-bool MemRefDependenceGraph::init() {
+/// Returns the memref being read/written by a memref/affine load/store op.
+static Value getMemRef(Operation *memOp) {
+  if (auto memrefLoad = dyn_cast<memref::LoadOp>(memOp))
+    return memrefLoad.getMemRef();
+  if (auto affineLoad = dyn_cast<AffineReadOpInterface>(memOp))
+    return affineLoad.getMemRef();
+  if (auto memrefStore = dyn_cast<memref::StoreOp>(memOp))
+    return memrefStore.getMemRef();
+  if (auto affineStore = dyn_cast<AffineWriteOpInterface>(memOp))
+    return affineStore.getMemRef();
+  llvm_unreachable("unexpected op");
+}
+
+/// Returns true if there may be a dependence on `memref` from srcNode's
+/// memory ops to dstNode's memory ops, while using the affine memory
+/// dependence analysis checks. The method assumes that there is at least one
+/// memory op in srcNode's loads and stores on `memref`, and similarly for
+/// `dstNode`. `srcNode.op` and `destNode.op` are expected to be nested in the
+/// same block and so the dependences are tested at the depth of that block.
+static bool mayDependence(const Node &srcNode, const Node &dstNode,
+                          Value memref) {
+  assert(srcNode.op->getBlock() == dstNode.op->getBlock());
+  if (!isa<AffineForOp>(srcNode.op) || !isa<AffineForOp>(dstNode.op))
+    return true;
+
+  // Conservatively handle dependences involving non-affine load/stores. Return
+  // true if there exists a conflicting read/write access involving such.
+  auto hasNonAffineDep = [&](ArrayRef<Operation *> srcOps,
+                             ArrayRef<Operation *> dstOps) {
+    return llvm::any_of(srcOps, [&](Operation *srcOp) {
+      Value srcMemref = getMemRef(srcOp);
+      if (srcMemref != memref)
+        return false;
+      return llvm::find_if(dstOps, [&](Operation *dstOp) {
+               return srcMemref == getMemRef(dstOp);
+             }) != dstOps.end();
+    });
+  };
+
+  SmallVector<Operation *> dstOps;
+  // Between non-affine src stores and dst load/store.
+  llvm::append_range(dstOps, llvm::concat<Operation *const>(
+                                 dstNode.loads, dstNode.stores,
+                                 dstNode.memrefLoads, dstNode.memrefStores));
+  if (hasNonAffineDep(srcNode.memrefStores, dstOps))
+    return true;
+  // Between non-affine loads and dst stores.
----------------
arnab-polymage wrote:

I have a question here. If src loads from a memref, and dest writes to it -- I'm not sure that there will there be any dependency

https://github.com/llvm/llvm-project/pull/156422