This helps avoid constant materialization for the patterns
InstCombine emits for something like INT_MIN <= X && x <= INT_MAX.
See top of changed test files for more detailed explanation.
I've enabled this for i16 when Zbb is enabled. sext.b did not seem
to be a benefit due to the constants folding into addi/sltiu.
This an alternative to https://reviews.llvm.org/D149814
We can enable this for i8 on rv32 when XVT is i64 and Zbb is enabled.
Before:
After: