* Multiplications by 2^X are turned into shifts. This factors code out of the

  getelementptr code path for use by other code paths (like malloc and alloca).
* Optimize comparisons with zero
* Generate neg, not, inc, and dec instructions, when possible.

This gives some code size wins, which might translate into performance.  We'll
see tommorow in the nightly tester.

llvm-svn: 9267