[Mlir-commits] [mlir] [mlir][dataflow] Cleanup liveness analysis (NFC) (PR #172874)

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Author: lonely eagle (linuxlonelyeagle)

<details>
<summary>Changes</summary>

In the implementation of visitBranchOperand within the LivenessAnalysis, there is logic to set the operand as live if its associated region has memory-effecting operations or if the return value of the branchOp is live. In this scenario, the subsequent call to the visitOperation function is redundant. Similarly, for cases where the operand should be set as dead, we also do not need to process it by calling visitOperation.

---
Full diff: https://github.com/llvm/llvm-project/pull/172874.diff


1 Files Affected:

- (modified) mlir/lib/Analysis/DataFlow/LivenessAnalysis.cpp (-28) 


``````````diff
diff --git a/mlir/lib/Analysis/DataFlow/LivenessAnalysis.cpp b/mlir/lib/Analysis/DataFlow/LivenessAnalysis.cpp
index 20be50c8e8a5b..71bf3cc5156d3 100644
--- a/mlir/lib/Analysis/DataFlow/LivenessAnalysis.cpp
+++ b/mlir/lib/Analysis/DataFlow/LivenessAnalysis.cpp
@@ -254,34 +254,6 @@ void LivenessAnalysis::visitBranchOperand(OpOperand &operand) {
       propagateIfChanged(argumentLiveness, argumentLiveness->markLive());
     }
   }
-
-  // Now that we have checked for memory-effecting ops in the blocks of concern,
-  // we will simply visit the op with this non-forwarded operand to potentially
-  // mark it "live" due to type (1.a/3) liveness.
-  SmallVector<Liveness *, 4> operandLiveness;
-  operandLiveness.push_back(getLatticeElement(operand.get()));
-  for (BlockArgument argument : argumentNotOperand)
-    operandLiveness.push_back(getLatticeElement(argument));
-  SmallVector<const Liveness *, 4> resultsLiveness;
-  for (const Value result : op->getResults())
-    resultsLiveness.push_back(getLatticeElement(result));
-  LDBG() << "Visiting operation for non-forwarded branch operand: "
-         << OpWithFlags(op, OpPrintingFlags().skipRegions());
-  (void)visitOperation(op, operandLiveness, resultsLiveness);
-
-  // We also visit the parent op with the parent's results and this operand if
-  // `op` is a `RegionBranchTerminatorOpInterface` because its non-forwarded
-  // operand depends on not only its memory effects/results but also on those of
-  // its parent's.
-  if (!isa<RegionBranchTerminatorOpInterface>(op))
-    return;
-  Operation *parentOp = op->getParentOp();
-  SmallVector<const Liveness *, 4> parentResultsLiveness;
-  for (const Value parentResult : parentOp->getResults())
-    parentResultsLiveness.push_back(getLatticeElement(parentResult));
-  LDBG() << "Visiting parent operation for non-forwarded branch operand: "
-         << *parentOp;
-  (void)visitOperation(parentOp, operandLiveness, parentResultsLiveness);
 }
 
 void LivenessAnalysis::visitCallOperand(OpOperand &operand) {

``````````

</details>


https://github.com/llvm/llvm-project/pull/172874