...

1. Use bseti when profitable.  Many cases of poor constant synthesis are failure to use bseti.
2. Use "uw" variants of shifts/arithmetic instructions when the constant has bit 0x80000000 set.
3. Use shNadd for constants evenly divisible by 9, 5 or 3.
4. Use blcri in conjunction with lui or addi to clear a small number of bits, particularly in the high 33 bits of a 64bit word
5. Adjust constant so low 13 bits are 0x1800, recursively re-synthesize and restore low bits with trailing addi.
6. Synthesize C' from C using bit inversion.  Synthesize C', then invert the result.  If that's better than synthesizing C directly, then use the inversion sequence.
7. Use pack for repeating constants
   1. Depends on reassociation of constant in logical ops with shifts
   2. Depends on basic Zbkb support
8. Use pack as synthesis of last resort

...

Updates

26 May 2024 

• Reassociation of constants in logical ops with shifts submitted upstream
• Using pack to handle constants with equal high/low halves implemented
• Synthesizing the inverted constant, then inverting the result submitted integrated upstream
• Adjusting the constant to have 0s in the low bits, synthesizing, then restoring low bits with addi integrated upstream.

...