[Mlir-commits] [mlir] [MLIR][SCF] Add checks to verify that the pipeliner schedule is correct. (PR #77083)

[Rik Huijzer]

================
@@ -330,6 +339,39 @@ LoopPipelinerInternal::getDefiningOpAndDistance(Value value) {
   return {def, distance};
 }
 
+/// Compute unrolled cycles of each op and verify that each op is scheduled
+/// after its operands (modulo the distance between producer and consumer).
+bool LoopPipelinerInternal::verifySchedule() {
+  int64_t numCylesPerIter = opOrder.size();
+  // Pre-compute the unrolled cycle of each op.
+  DenseMap<Operation *, int64_t> unrolledCyles;
+  for (int64_t cycle = 0; cycle < numCylesPerIter; cycle++) {
+    Operation *def = opOrder[cycle];
+    auto it = stages.find(def);
+    assert(it != stages.end());
+    int64_t stage = it->second;
+    unrolledCyles[def] = cycle + stage * numCylesPerIter;
+  }
+  for (Operation *consumer : opOrder) {
+    int64_t consumerCycle = unrolledCyles[consumer];
+    for (Value operand : consumer->getOperands()) {
+      auto [producer, distance] = getDefiningOpAndDistance(operand);
+      if (!producer)
+        continue;
+      auto it = unrolledCyles.find(producer);
+      // Skip producer coming from outside the loop.
+      if (it == unrolledCyles.end())
+        continue;
+      int64_t producerCycle = it->second;
+      if (consumerCycle < producerCycle - numCylesPerIter * distance) {
+        consumer->emitError("operation scheduled before its operands.");
----------------
rikhuijzer wrote:

```suggestion
        consumer->emitError("operation (consumer) scheduled before its operands (producer)");
```
nit: The consumer and producer mention makes the error more clear.

For the dot, I see basically no `emitError` messages in MLIR that end with a dot so probably best to remove that one.

https://github.com/llvm/llvm-project/pull/77083