loongarch: avoid unnecessary sign-extend after 32-bit division

Like add.w/sub.w/mul.w, div.w/mod.w/div.wu/mod.wu also sign-extend the
output on LA64.  But, LoongArch v1.00 mandates that the inputs of 32-bit
division to be sign-extended so we have to expand 32-bit division into
RTL sequences.

We defined div.w/mod.w/div.wu/mod.wu as a (DI, DI) -> SI instruction.
This definition does not indicate the fact that these instructions will
store the result as sign-extended value in a 64-bit GR.  Then the
compiler would emit unnecessary sign-extend operations.  For example:

    int div(int a, int b) { return a / b; }

was compiled to:

    div.w  $r4, $r4, $r5
    slli.w $r4, $r4, 0    # this is unnecessary
    jr     $r1

To remove this unnecessary operation, we change the division
instructions to (DI, DI) -> DI and describe the sign-extend behavior
explicitly in the RTL template.  In the expander for 32-bit division we
then use simplify_gen_subreg to extract the lower 32 bits.

gcc/ChangeLog:

	* config/loongarch/loongarch.md (<any_div>di3_fake): Describe
	the sign-extend of result in the RTL template.
	(<any_div><mode>3): Adjust for <any_div>di3_fake change.

gcc/testsuite/ChangeLog:

	* gcc.target/loongarch/div-4.c: New test.

0 files changed, 0 insertions, 0 deletions