[Bug tree-optimization/55970] New: [x86] Avoid reverse order of function argument gimplifying

[ysrumyan at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55970



             Bug #: 55970

           Summary: [x86] Avoid reverse order of function argument

                    gimplifying

    Classification: Unclassified

           Product: gcc

           Version: unknown

            Status: UNCONFIRMED

          Severity: normal

          Priority: P3

         Component: tree-optimization

        AssignedTo: unassig...@gcc.gnu.org

        ReportedBy: ysrum...@gmail.com





One important customer met with this problem in a process of porting app from

ARN to IA. The issue can be illustrated by attached example and essential for

x86 platform since only it defines 'PUSH_ARGS_REVERSED' macros. Note also that

attached code is not compliant with C99 standard since it assume definite order

of argument calculation.



gcc -O3 t.c t_main.c

./a.out

Test Failed

gcc -O3 t.c t_main_fix.c              

./a.out 

Test Passed



diff t_main.c t_main_fix.c

13c13,14

<   if (foo (foo1(), foo1()))

---

>   int x1 = foo1(), x2 = foo1();

>   if (foo (x1, x2))



You can see that gimplifying of function arguments (gimplify.c,

dimplify_call_expr) uses reverse order of arguments:



  /* Finally, gimplify the function arguments.  */

  if (nargs > 0)

    {

      for (i = (PUSH_ARGS_REVERSED ? nargs - 1 : 0);

           PUSH_ARGS_REVERSED ? i >= 0 : i < nargs;

           PUSH_ARGS_REVERSED ? i-- : i++)

        {

...



I assume that we must no use reverse order in this place, i.e. loop header must

look like

      for (i = 0; i < nargs; i++)