[llvm-branch-commits] [mlir] [mlir][Transforms] `remove-dead-values`: Rely on canonicalizer for region simplification (PR #173505)

[Matthias Springer via llvm-branch-commits]

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@@ -751,11 +517,44 @@ static void processBranchOp(BranchOpInterface branchOp, RunLivenessAnalysis &la,
   }
 }
 
+/// Create ub.poison ops for the given values. If a value has no uses, return
+/// an "empty" value.
+static SmallVector<Value> createPoisonedValues(OpBuilder &b,
+                                               ValueRange values) {
+  return llvm::map_to_vector(values, [&](Value value) {
+    if (value.use_empty())
+      return Value();
+    return ub::PoisonOp::create(b, value.getLoc(), value.getType()).getResult();
+  });
+}
+
+namespace {
+/// A listener that keeps track of ub.poison ops.
+struct TrackingListener : public RewriterBase::Listener {
+  void notifyOperationErased(Operation *op) override {
+    if (auto poisonOp = dyn_cast<ub::PoisonOp>(op))
+      poisonOps.erase(poisonOp);
+  }
+  void notifyOperationInserted(Operation *op,
+                               OpBuilder::InsertPoint previous) override {
+    if (auto poisonOp = dyn_cast<ub::PoisonOp>(op))
+      poisonOps.insert(poisonOp);
+  }
+  DenseSet<ub::PoisonOp> poisonOps;
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matthias-springer wrote:

I would keep this one as a regular `DenseSet`. It is expected to be larger than the other `DenseSet` above because it tracks `ub.poison` ops across the entire pass application.


https://github.com/llvm/llvm-project/pull/173505