On 11/10/22 07:37, Lin Sinan via Gcc-patches wrote:
> The motivation of this patch is to correct the wrong estimation of the number of instructions needed for loading a 64bit constant in rv32 in the current cost model(riscv_interger_cost). According to the current implementation, if a constant requires more than 3 instructions(riscv_const_insn and riscv_legitimate_constant_p), then the constant will be put into constant pool when expanding gimple to rtl(legitimate_constant_p hook and emit_move_insn). So the inaccurate cost model leads to the suboptimal codegen in rv32 and the wrong estimation part could be corrected through this fix.
> 
> e.g. the current codegen for loading 0x839290001 in rv32
> 
>    lui     a5,%hi(.LC0)
>    lw      a0,%lo(.LC0)(a5)
>    lw      a1,%lo(.LC0+4)(a5)
> .LC0:
>    .word   958988289
>    .word   8
> 
> output after this patch
> 
>    li a0,958988288
>    addi a0,a0,1
>    li a1,8
> 
> gcc/ChangeLog:
> 
>          * config/riscv/riscv.cc (riscv_build_integer): Handle the case of loading 64bit constant in rv32.
> 
> gcc/testsuite/ChangeLog:
> 
>          * gcc.target/riscv/rv32-load-64bit-constant.c: New test.
> 
> Signed-off-by: Lin Sinan <sinan.lin@linux.alibaba.com>
I fixed up the ChangeLog and some minor formatting issues in the new 
code in riscv_build_integer.  I also twiddled the test so that it 
iterates over the optimization levels properly while skipping -O0.

Attached is the patch I committed.

jeff