C is a constant which can be sign-extended from 8 bits without value loss,
and op is one of: add, sub, imul, and, or, xor.
This allows the JIT to emit the one byte version of the constant instead of
the two or 4 byte version. Because these instructions are very common, this
can save a LOT of code space. For example, I sampled two benchmarks, 176.gcc
and 254.gap.
BM Old New Reduction
176.gcc 2673621 2548962 4.89%
254.gap 498261 475104 4.87%
Note that while the percentage is not spectacular, this did eliminate
124.6 _KILOBYTES_ of codespace from gcc. Not bad.
Note that this doesn't effect the llc version at all, because the assembler
already does this optimization.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@9284 91177308-0d34-0410-b5e6-96231b3b80d8
