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
40a89da65c