[Bug c++/69008] New: gcc emits unneeded memory access when passing trivial structs by value (ARM)

[gcc at bobbyperu dot info]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69008

            Bug ID: 69008
           Summary: gcc emits unneeded memory access when passing trivial
                    structs by value (ARM)
           Product: gcc
           Version: 5.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gcc at bobbyperu dot info
  Target Milestone: ---

gcc is emitting unneeded memory accesses in this code snippet.
Trivial structs up to 16 bytes are passed in r0-r3, no need for stack.

struct Trivial {
    int i1;
    int i2;
};

int foo(Trivial t)
{
    return t.i1 + t.i2;
}

gcc on armv7:
$ g++ arm.cpp -O2 -mabi=aapcs -c -S && cat arm.s
  sub     sp, sp, #8
  add     r3, sp, #8
  stmdb   r3, {r0, r1}
  ldmia   sp, {r0, r3}
  add     r0, r0, r3
  add     sp, sp, #8
  bx      lr

clang:
$ clang++ arm.cpp -O2 -mabi=aapcs -c -S && cat arm.s

add r0, r0, r1
bx  lr