[Bug other/109435] New: [MIPS64R6] Typedef struct alignment returns incorrect results

[jovan.dmitrovic at syrmia dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109435

            Bug ID: 109435
           Summary: [MIPS64R6] Typedef struct alignment returns incorrect
                    results
           Product: gcc
           Version: 10.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jovan.dmitrovic at syrmia dot com
  Target Milestone: ---

Consider the following testcase:


#include<stdio.h>

typedef struct uint8 {
  unsigned v[8];
} uint8 __attribute__ ((aligned(128)));

unsigned callee(int x, uint8 a) {
    return a.v[0];
}

uint8 identity(uint8 in) {
    return in;
}

int main() {
    uint8 vec = {1, 2, 3, 4, 5, 6, 7, 8};
    printf("res1: %d\n", callee(99, identity(vec)));
    uint8 temp = identity(vec);
    printf("res2: %d\n", callee(99, temp));
}


When this code is compiled for MIPS64 R6, output is as follows:

res1: 3
res2: 1

However, when aligned attribute is removed from the testcase, res1 and res2
become 1,
which are values that were expected in the first place. 
Furthermore, this bug is reproducible only if there is a unused argument x in
function callee. Adding more arguments or switching their places also produces
expected values. Type of x doesn't seem to impact the result.