[Bug middle-end/65315] New: incorrect alignment of local variable with aligned attribute

[sje at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65315

            Bug ID: 65315
           Summary: incorrect alignment of local variable with aligned
                    attribute
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sje at gcc dot gnu.org

Created attachment 34953
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=34953&action=edit
Test case

When GCC has multiple local variables with different aligned attributes on
them, it creates an aligned block of space aligned to the least aligned
variable instead of the most aligned variable.

In the attached program, when run on MIPS, GCC is creating a 32 byte aligned
block of memory for foo1, foo3, and foo4 and a 128 byte aligned memory block
for foo2.  foo3 and foo4 should have 128 byte aligned memory.

I thought the problem was in stack_var_cmp where it checks the alignment of
two variables and returns '(int) largeb - (int) largea' to sort the variables
based on their alignment but when I swapped the two arguments I got an ICE
in expand_stack_vars [gcc_assert (large_base != NULL);].

It also tried changing:

large_align = stack_vars[stack_vars_sorted[0]].alignb * BITS_PER_UNIT;

to

large_align = stack_vars[stack_vars_sorted[n-1]].alignb * BITS_PER_UNIT;

but that caused the same ICE.

It may be that we need a loop to check the alignment of each variable.