🚀 go-pugleaf

A bug exists in function.c (version 2.7.0), in the function:
'fixup_var_refs_1'.

Bug:     The function 'single_set' is called from two different places
         with the wrong type of argument. It should be changed from
         'PATTERN (insn)' to 'insn'.

Symptom: The bug causes 'single_set' to always return 0. This will
         cause an unnecessary copying via a new pseudo register.
         There will probably be no visible differences, since this
         copying is likely to be removed when optimizing.

The following program might be helpful when examining the bug:

  void main ()
  {
    double a;
    
    a = 3.0;
    fun (&a);
  }

Compile with/without optimization and compare the .rtl files. The extra
copying should appear on any platform (we believe). The compiler will
first put the variable 'a' in a register. When the address of 'a'
is needed it must fix up all var refs to change them into a stack slot
instead. This is were it fails, instead of just changing the references,
it inserts extra code to make a copying via a pseudo register.

============================================================ Bug fix:
*** function.c.2.7.0      Wed Nov 22 15:25:33 1995
--- function.c.fixed      Wed Nov 22 15:26:28 1995
***************
*** 1934,1946 ****
        if ((SET_SRC (x) == var
             || (GET_CODE (SET_SRC (x)) == SUBREG
                 && SUBREG_REG (SET_SRC (x)) == var))
            && (GET_CODE (SET_DEST (x)) == REG
                || (GET_CODE (SET_DEST (x)) == SUBREG
                    && GET_CODE (SUBREG_REG (SET_DEST (x))) == REG))
!           && x == single_set (PATTERN (insn)))
          {
            rtx pat;
  
            replacement = find_fixup_replacement (replacements, SET_SRC (x));
            if (replacement->new)
              SET_SRC (x) = replacement->new;
--- 1934,1946 ----
        if ((SET_SRC (x) == var
             || (GET_CODE (SET_SRC (x)) == SUBREG
                 && SUBREG_REG (SET_SRC (x)) == var))
            && (GET_CODE (SET_DEST (x)) == REG
                || (GET_CODE (SET_DEST (x)) == SUBREG
                    && GET_CODE (SUBREG_REG (SET_DEST (x))) == REG))
!           && x == single_set (insn))
          {
            rtx pat;
  
            replacement = find_fixup_replacement (replacements, SET_SRC (x));
            if (replacement->new)
              SET_SRC (x) = replacement->new;
***************
*** 1979,1991 ****
        if ((SET_DEST (x) == var
             || (GET_CODE (SET_DEST (x)) == SUBREG
                 && SUBREG_REG (SET_DEST (x)) == var))
            && (GET_CODE (SET_SRC (x)) == REG
                || (GET_CODE (SET_SRC (x)) == SUBREG
                    && GET_CODE (SUBREG_REG (SET_SRC (x))) == REG))
!           && x == single_set (PATTERN (insn)))
          {
            rtx pat;
  
            if (GET_CODE (SET_DEST (x)) == SUBREG)
              SET_DEST (x) = fixup_memory_subreg (SET_DEST (x), insn, 0);
            else
--- 1979,1991 ----
        if ((SET_DEST (x) == var
             || (GET_CODE (SET_DEST (x)) == SUBREG
                 && SUBREG_REG (SET_DEST (x)) == var))
            && (GET_CODE (SET_SRC (x)) == REG
                || (GET_CODE (SET_SRC (x)) == SUBREG
                    && GET_CODE (SUBREG_REG (SET_SRC (x))) == REG))
!           && x == single_set (insn))
          {
            rtx pat;
  
            if (GET_CODE (SET_DEST (x)) == SUBREG)
              SET_DEST (x) = fixup_memory_subreg (SET_DEST (x), insn, 0);
            else
============================================================


Regards,

Thomas Lundqvist, d0thomas@dtek.chalmers.se
Harry Gunnarson, d1harry@dtek.chalmers.se


(The bug was found when doing a port to Thor, a microprocessor
designed at Saab Ericsson Space AB, which have a stack-based
instruction set and 2 delay slots. For more information send
e-mail to thor@space.se)