[Bug target/71106] New: MIPS: Unaligned load/store instructions are not used to access a variable with an aligned attribute

[andrew.bennett at imgtec dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71106

            Bug ID: 71106
           Summary: MIPS: Unaligned load/store instructions are not used
                    to access a variable with an aligned attribute
           Product: gcc
           Version: 6.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: andrew.bennett at imgtec dot com
  Target Milestone: ---

Hi,

Currently if we build the following example for MIPS:

int a __attribute__((aligned(1)));

void
foo (void)
{
  a = 0;
}

Using the following command line options:

-mips32r2 -O2 -mno-gpopt

It generates a sw instruction to store the value of 0 to the variable a, when
it should be using a swl/swr instruction sequence because the value of the
aligned attribute is less than the natural alignment of the int type.

        .ent    foo
        .type   foo, @function
foo:
        .frame  $sp,0,$31               # vars= 0, regs= 0/0, args= 0, gp= 0
        .mask   0x00000000,0
        .fmask  0x00000000,0
        .set    noreorder
        .set    nomacro
        lui     $2,%hi(a)
        jr      $31
        sw      $0,%lo(a)($2)

        .set    macro
        .set    reorder
        .end    foo
        .size   foo, .-foo

        .comm   a,4,1