[Bug target/86387] [RISCV][ABI] GCC fails to sign/zero-ext integers as necessary for passing/returning int+fp structs on with hard-float ABIs

["asb at lowrisc dot org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86387

Alex Bradbury <asb at lowrisc dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[RISCV][ABI] GCC fails to   |[RISCV][ABI] GCC fails to
                   |sign/zero-ext integers as   |sign/zero-ext integers as
                   |necessary for return of     |necessary for
                   |int+fp structs in with      |passing/returning int+fp
                   |hard-float ABIs             |structs on with hard-float
                   |                            |ABIs

--- Comment #1 from Alex Bradbury <asb at lowrisc dot org> ---
Changing title as this bug affects both return and argument passing. I could
create a separate bug report if preferred, but the issues seem so closely
related it might make most sense to keep here.

No sign or zero-extension takes place in the following example, but as-per the
ABI it should.

I actually sought clarification on this aspect of the ABI last September, to
perhaps this is a regression in GCC behaviour?
https://github.com/riscv/riscv-elf-psabi-doc/issues/37

$ cat foo.c 
#include <stdint.h>

struct s_u8_f { uint8_t i; float f; };
struct s_i8_f { int8_t i;  float f; };

void must_receive_zext_arg(struct s_u8_f);
void must_receive_sext_arg(struct s_i8_f);

void should_zext_arg(int8_t i, float f) {
  struct s_u8_f s;
  s.i = i;
  s.f = f;
  must_receive_zext_arg(s);
}

void should_sext_arg(uint8_t i, float f) {
  struct s_i8_f s;
  s.i = i;
  s.f = f;
  must_receive_sext_arg(s);
}

./riscv32-unknown-elf-gcc -march=rv32imf -mabi=ilp32f foo.c -S -o - -O1
        .file   "foo.c"
        .option nopic
        .text
        .align  2
        .globl  should_zext_arg
        .type   should_zext_arg, @function
should_zext_arg:
        addi    sp,sp,-32
        sw      ra,28(sp)
        call    must_receive_zext_arg
        lw      ra,28(sp)
        addi    sp,sp,32
        jr      ra
        .size   should_zext_arg, .-should_zext_arg
        .align  2
        .globl  should_sext_arg
        .type   should_sext_arg, @function
should_sext_arg:
        addi    sp,sp,-32
        sw      ra,28(sp)
        call    must_receive_sext_arg
        lw      ra,28(sp)
        addi    sp,sp,32
        jr      ra
        .size   should_sext_arg, .-should_sext_arg
        .ident  "GCC: (GNU) 9.0.0 20180703 (experimental)"