[Canonicalize] Don't call isBeforeInBlock in OperationFolder::tryToFold.

This patch (e4635e6328) fixed a bug where a newly generated/reused
constant wouldn't dominate a folded operation.  It did so by calling
isBeforeInBlock to move the constant around on demand.  This introduced
a significant compile time regression, because "isBeforeInBlock" is
O(n) in the size of a block the first time it is called, and the cache
is invalidated any time canonicalize changes something big in the block.

This fixes LLVM PR51738 and this CIRCT issue:
https://github.com/llvm/circt/issues/1700

This does affect the order of constants left in the top of a block,
I staged in the testsuite changes in rG42431b8207a5.

Differential Revision: https://reviews.llvm.org/D109454

mlir/lib/Transforms/Utils/FoldUtils.cpp

@@ -236,10 +236,9 @@ LogicalResult OperationFolder::tryToFold(
       // Ensure that this constant dominates the operation we are replacing it
       // with. This may not automatically happen if the operation being folded
       // was inserted before the constant within the insertion block.
-      if (constOp->getBlock() == op->getBlock() &&
-          !constOp->isBeforeInBlock(op)) {
-        constOp->moveBefore(op);
-      }
+      Block *opBlock = op->getBlock();
+      if (opBlock == constOp->getBlock() && &opBlock->front() != constOp)
+        constOp->moveBefore(&opBlock->front());
 
       results.push_back(constOp->getResult(0));
       continue;