[mlir][dataflow] Allow re-run all analyses in DataFlowSolver (#120881)

In downstream (check google/heir#1228,
especially [this
commit](ZenithalHourlyRate/heir@fbf0b27);
also check google/heir#1154) we often need to
re-run the analysis during the transformation pass as IR get changed
based on the analysis result and analysis continuously get invalidated.

There are solutions to it like `getOrCreateState` for newly created
`Value` (`AnchorT`), but warning is that the new state does not
propagate! This is quite unexpected as user of analysis would expect it
to propagate. We downstream used to use `solver->propagateIfChanged` but
that turned out to be not working, see detailed writeup in
google/heir#1153.

Just call `initializeAndRun` repeatedly also does not solve the problem
as `analysisStates` is not cleared and the monotonicity of
`AnalysisState` will make the analysis invalid as `join` will not work
as expected (the first join is no longer `join(uninitialized, init
value)`, instead it becomes `join(higher value, init value)`.

To correctly re-run the analysis, either a new `DataFlowSolver` is
created, or we can just clear the `analysisState`.

Author: ZenithalHourlyRate

mlir/include/mlir/Analysis/DataFlowFramework.h

@@ -308,6 +308,10 @@ class DataFlowConfig {
 ///    according to their dependency relations until a fixed point is reached.
 /// 3. Query analysis state results from the solver.
 ///
+/// Steps to re-run a data-flow analysis when IR changes:
+/// 1. Erase all analysis states as they are no longer valid.
+/// 2. Re-run the analysis using `initializeAndRun`.
+///
 /// TODO: Optimize the internal implementation of the solver.
 class DataFlowSolver {
 public:
@@ -346,6 +350,9 @@ class DataFlowSolver {
     }
   }
 
+  // Erase all analysis states
+  void eraseAllStates() { analysisStates.clear(); }
+
   /// Get a uniqued lattice anchor instance. If one is not present, it is
   /// created with the provided arguments.
   template <typename AnchorT, typename... Args>