[MLIR][Affine] Make isValidLoopInterchangePermutation efficient (#128863)

Avoid doing dependency checks for the trivial case when size of `loops`
is 1.

Author: arnab-polymage

mlir/lib/Dialect/Affine/Utils/LoopUtils.cpp

@@ -1351,10 +1351,12 @@ static bool checkLoopInterchangeDependences(
 /// nested sequence of loops in 'loops' would violate dependences.
 bool mlir::affine::isValidLoopInterchangePermutation(
     ArrayRef<AffineForOp> loops, ArrayRef<unsigned> loopPermMap) {
+  assert(loopPermMap.size() == loops.size() && "invalid loop perm map");
+  unsigned maxLoopDepth = loops.size();
+  if (maxLoopDepth == 1)
+    return true;
   // Gather dependence components for dependences between all ops in loop nest
   // rooted at 'loops[0]', at loop depths in range [1, maxLoopDepth].
-  assert(loopPermMap.size() == loops.size());
-  unsigned maxLoopDepth = loops.size();
   std::vector<SmallVector<DependenceComponent, 2>> depCompsVec;
   getDependenceComponents(loops[0], maxLoopDepth, &depCompsVec);
   return checkLoopInterchangeDependences(depCompsVec, loops, loopPermMap);