Revert "[Reassociate] Drop weight reduction to fix issue 91417 (#91469)" (#94210)

Reverts
https://github.com/llvm/llvm-project/commit/3bcccb6af685c3132a9ee578b9e11b2503c35a5c
and
https://github.com/llvm/llvm-project/commit/9a282724a29899e84adc91bdeaf639010408a80d
because #91469 causes a miscompilation
https://github.com/llvm/llvm-project/pull/91469#discussion_r1623925158.