Rearchitect -Wconversion and -Wsign-compare.  Instead of computing them
"bottom-up" when implicit casts and comparisons are inserted, compute them
"top-down" when the full expression is finished.  Makes it easier to
coordinate warnings and thus implement -Wconversion for signedness
conversions without double-warning with -Wsign-compare.  Also makes it possible
to realize that a signedness conversion is okay because the context is
performing the inverse conversion.  Also simplifies some logic that was
trying to calculate the ultimate comparison/result type and getting it wrong.
Also fixes a problem with the C++ explicit casts which are often "implemented"
in the AST with a series of implicit cast expressions.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@103174 91177308-0d34-0410-b5e6-96231b3b80d8
11 files changed