[Mlir-commits] [mlir] [mlir][ArmSME] Use liveness information in the tile allocator (PR #90448)

[Andrzej Warzyński]

================
@@ -116,4 +116,50 @@ VectorType getSMETileTypeForElement(Type elementType) {
   return VectorType::get({minNumElts, minNumElts}, elementType, {true, true});
 }
 
+void eraseTriviallyDeadTileOps(IRRewriter &rewriter,
+                               FunctionOpInterface function) {
+  SmallVector<Operation *> worklist;
+  function->walk([&](Operation *op) {
+    auto armSMEOp = dyn_cast<arm_sme::ArmSMETileOpInterface>(op);
+    if (armSMEOp && isOpTriviallyDead(armSMEOp))
+      worklist.push_back(armSMEOp);
+  });
+  while (!worklist.empty()) {
+    Operation *op = worklist.pop_back_val();
+    if (!isOpTriviallyDead(op))
+      continue;
+    for (Value value : op->getOperands()) {
+      if (auto armSMEOp = value.getDefiningOp<arm_sme::ArmSMETileOpInterface>())
+        worklist.push_back(armSMEOp);
+    }
+    rewriter.eraseOp(op);
+  }
+}
+
+bool isTriviallyCloneableTileOp(arm_sme::ArmSMETileOpInterface tileOp) {
+  return tileOp && tileOp->getNumResults() == 1 &&
+         tileOp->getNumOperands() == 0 && isPure(tileOp);
+}
----------------
banach-space wrote:

Please document:
```
/// A helper function that helps to filter out Ops that are not trivial to clone. Conditions that are checked:
///   * no more than one result/operand - otherwise we'd have to investigate these as well,
///   * pure - otherwise we'd need to reason whether moving/duplicating might change the semantics. 
```

Also, the name of this function suggests that the input is an actual Operation. Could you update like this:
```cpp
bool isTriviallyCloneableTileOp(arm_sme::ArmSMETileOpInterface tileOp) {
  assert(tileOp && "Expected an operation producing an SME tile");
  
  return tileOp->getNumResults() == 1 &&
         tileOp->getNumOperands() == 0 && isPure(tileOp);
}
```
And then, when this hook is used (modulo formatting):
```cpp
if (!operandTileOpt)
            return tileOp.emitOpError("cannot clone a block argument - failed to rectify tile operand with tile "
                                      "result (move required)");
if (!isTriviallyCloneableTileOp(operandTileOp))
            return tileOp.emitOpError("not a trivially clonable Op - failed to rectify tile operand with tile "
                                      "result (move required)");
```

In general, lets diagnose and document reasons for failure as early and verbosely as possible (within reason).

https://github.com/llvm/llvm-project/pull/90448