(jump_optimize): Delete insns that set registers that are not used elsewhere.

(jump_optimize): Delete insns that set registers that are not used elsewhere.
Fix some bugs in "if (...) x = a; else x = b;" code.
Remove uses of reorder_insns.
Add code to make scc insns for "if (...) x = exp;" if EXP is simple enough.
Optimize "if (...) x = b;" if jumps very expensive; don't use a REG as the
older value of X since it doesn't help and can hurt.
Correctly place generated insns in above case.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@2191 138bc75d-0d04-0410-961f-82ee72b054a4