[to-be-committed,RISC-V] Improve usage of slli.uw in constant synthesis
And an improvement to using slli.uw...
I recently added the ability to use slli.uw in the synthesis path. That
code was conditional on the right justified constant being a LUI_OPERAND
after sign extending from bit 31 to bit 63.
That code is working fine, but could be improved. Specifically there's
no reason it shouldn't work for LUI+ADDI under the same circumstances.
So rather than testing the sign extended, right justified constant is a
LUI_OPERAND, we can just test that the right justified constant has
precisely 32 leading zeros.
gcc/
* config/riscv/riscv.cc (riscv_build_integer_1): Use slli.uw more.
gcc/testsuite
* gcc.target/riscv/synthesis-5.c: New test.