[mlir] Allow RegionBranchOps in dependence analysis.

[tpopp]

Summary

This is to prevent assertion failures on scf.if and shape.assuming
operations where this is not enough information currently to handle any
aliasing information.

[nicolasvasilache]

As discussed offline, this will be revamped in a relatively near future.
Fine to unblock for now assuming presubmits pass.

mlir/lib/Dialect/Linalg/Analysis/DependenceAnalysis.cpp

Value Aliases::find(Value v) {
   while (true) {
     if (v.isa<BlockArgument>())
       return v;
 
     Operation *defOp = v.getDefiningOp();
     if (!defOp)
       return v;
 
+    // Treat RegionBranchOpInterfaces like an allocate and don't try to follow
+    // the aliasing further.
+    if (isa<RegionBranchOpInterface>(defOp))
+      return v;
     if (isa<TensorToMemrefOp>(defOp))
       return v;
 
     if (auto memEffect = dyn_cast<MemoryEffectOpInterface>(defOp)) {
       // Collect all memory effects on `v`.
       SmallVector<MemoryEffects::EffectInstance, 1> effects;
       memEffect.getEffectsOnValue(v, effects);