PR23608 pointed out that using the preheader to gain a context instruction isn't always legal because a loop might not have a preheader. When looking into that, I realized that using the preheader to determine legality for sinking is questionable at best. Given no test covers that case and the original commit didn't seem to intend it, I restructured the code to only ask context sensative queries for hoising of loads and stores. This is effectively a partial revert of 237593.
llvm-svn: 237985
db94a30be3