[Mlir-commits] [mlir] [mlir][dataflow] Add visitBranchRegionArgument interface to SparseBackwardDataFlowAnalysis and apply it in LivenessAnalysis/RemoveDeadValues (PR #169816)

[Oleksandr Alex Zinenko]

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@@ -244,24 +224,12 @@ void LivenessAnalysis::visitBranchOperand(OpOperand &operand) {
     Liveness *operandLiveness = getLatticeElement(operand.get());
     LDBG() << "Marking branch operand live: " << operand.get();
     propagateIfChanged(operandLiveness, operandLiveness->markLive());
-    for (BlockArgument argument : argumentNotOperand) {
-      Liveness *argumentLiveness = getLatticeElement(argument);
-      LDBG() << "Marking RegionBranchOp's argument live: " << argument;
-      // TODO: this is overly conservative: we should be able to eliminate
-      // unused values in a RegionBranchOpInterface operation but that may
-      // requires removing operation results which is beyond current
-      // capabilities of this pass right now.
-      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()));
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ftynse wrote:

So now we are not passing operands in at all? Why? We will be passing an empty `operands` list to `visitOperation`, which will then have no effect since it can only modify `opreands` lattices so all this code becomes dead. I suspect we still want to visit operands here, but please double check and add a test, with synthetic operations that can go into the test dialect if needed.

https://github.com/llvm/llvm-project/pull/169816