Analyze shared memory alias (#81)

The purpose of this PR is analyzing shared memory aliases so that we can
fix memory allocation bugs and save memory allocations in triton code
involving complex control flows.

Changes to memory bar and allocation are on the way.

Co-authored-by: Philippe Tillet <phil@openai.com>

lib/Analysis/Alias.cpp

@@ -0,0 +1,66 @@
+#include "triton/Analysis/Alias.h"
+#include "triton/Analysis/Utility.h"
+#include "triton/Dialect/TritonGPU/IR/Dialect.h"
+
+namespace mlir {
+
+AliasInfo AliasInfo::join(const AliasInfo &lhs, const AliasInfo &rhs) {
+  if (lhs == rhs)
+    return lhs;
+  AliasInfo ret;
+  for (auto value : lhs.allocs) {
+    ret.insert(value);
+  }
+  for (auto value : rhs.allocs) {
+    ret.insert(value);
+  }
+  return ret;
+}
+
+ChangeResult SharedMemoryAliasAnalysis::visitOperation(
+    Operation *op, ArrayRef<LatticeElement<AliasInfo> *> operands) {
+  AliasInfo aliasInfo;
+  bool pessimistic = true;
+  if (maybeSharedAllocationOp(op)) {
+    // These ops will allocate a new shared memory buffer.
+    auto result = op->getResult(0);
+    if (isSharedEncoding(result)) {
+      aliasInfo.insert(result);
+      pessimistic = false;
+    }
+  } else {
+    llvm::errs() << "op: " << op->getName() << "\n";
+  }
+  // XXX(Keren): triton ops don't support aliasing yet.
+  // else if (auto viewOp = dyn_cast<triton::ViewOp>(op) ||
+  //                         dyn_cast<triton::ExpandDimsOp>(op)) {
+  //  // These ops will reate a new view of the same shared memory buffer.
+  //  auto result = op->getResult(0);
+  //  if (isSharedEncoding(result)) {
+  //    aliasInfo = AliasInfo(operands[0]->getValue());
+  //    pessimistic = false;
+  //  }
+  //}
+  if (pessimistic) {
+    return markAllPessimisticFixpoint(op->getResults());
+  }
+  // Join all latice elements
+  ChangeResult result = ChangeResult::NoChange;
+  for (Value value : op->getResults()) {
+    result |= getLatticeElement(value).join(aliasInfo);
+  }
+  return result;
+}
+
+AliasResult SharedMemoryAliasAnalysis::alias(Value lhs, Value rhs) {
+  // TODO: implement
+  return AliasResult::MayAlias;
+}
+
+ModRefResult SharedMemoryAliasAnalysis::getModRef(Operation *op,
+                                                  Value location) {
+  // TODO: implement
+  return ModRefResult::getModAndRef();
+}
+
+} // namespace mlir