[ValueTracking] readnone CallInsts are fair game for speculation

Any call which is side effect free is trivially OK to speculate.  We
already had similar logic in EarlyCSE and GVN but we were missing it
from isSafeToSpeculativelyExecute.

This fixes PR24601.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@246232 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed