When instructions add, and, or, xor, and movd have
constant operands in some cases more instructions are
generated than necessary by the assembler.
This adds more opcode/operand combinations to the optab
and improves the code generation for the cases where the
size and sign of the constant allows the use of 1
instructions instead of 2.
Example of previous code:
oris r3, r0, 0
ori r3, r3, 65533
now:
ori r3, r0, 65533
This does not significantly reduce the overall binary size
because the improvement depends on the constant value.
Some procedures show a 1-2% reduction in size. This improvement
could also be significant in cases where the extra instructions
occur in a critical loop.
Testcase ppc64enc.s was added to cmd/asm/internal/asm/testdata
with the variations affected by this change.