[DAGCombine] visitREM - Don't assume that one divrem isn't driving another

Under some circumstances the divrems won't have been combined together before getting to this code.

So replace the assertion with a if() guard to not expand to X-((X/C)*C) to give the other combine chance to happen.

Reduced from OSS-Fuzz #6883
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=6883


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@327424 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed