Fix for GCC Bugzilla Bug 36134

["Gunnar Von Boehn" <gunnar at genesi-usa dot com>]

Hi,

Andreas Schwab, asked me do email here again,
the test case and the patch that are included to the GCC bugtracker of
Bug 36134.


Problem desciption:
---------------------------
The 68K/Coldfire backend uses 6 byte long ADDA.L instructions where
the shorter LEA instruction could be used .
The reason for this is that the 68K-backend does not keep track of
instruction size costs but only of the clocks per instructions.
This means if several possible instruction are equally fast (both need
just 1 clock in above case) the GCC-68k-backend
is not able to pick the shorter instruction but will just use the
first instruction matching the criteria.


Fix:
----
But shorter LEA before ADDA in the list of available instructions.


How to reproduce:
-------------------------
Code:
Compile this example function with:
m68k-linux-gnu-gcc -mcpu=54455 -msoft-float -o example -Os
-fomit-frame-pointer example.c
void * copy_32x4a(void *destparam, const void *srcparam, size_t size)
{
        int *dest = destparam;
        const int *src = srcparam;
        int size32;
        size32 = size / 16;
        for (; size32; size32--) {
                *dest++ = *src++;
                *dest++ = *src++;
                *dest++ = *src++;
                *dest++ = *src++;
        }
}

The resulting code will include two x 6 byte long ADDA instructions
 d3fc 0000 0010  addal #16,%a1
 d1fc 0000 0010  addal #16,%a0

Apply patch and compile again
The code will now include two x 4 byte long LEA instrustions
This is better as LEA is optimized for pipelining (with destination
forwarding) and is shorter than ADDA.L


Please be so kind and apply this patch.


A future improvement could be to include instruction LENGTH information into
the 68K/Coldfire backend to allow the Compiler to choose instructions
on code size decisions.


Many thanks in advance

Kind regards

Gunnar von Boehn

*** ../../../../gcc-4.4-20080523.ori/gcc/config/m68k/m68k.md	2008-05-14 14:24:43.000000000 +0200
--- m68k.md	2008-05-29 14:33:03.000000000 +0200
***************
*** 2323,2333 ****
    "! TARGET_COLDFIRE"
    "* return output_addsi3 (operands);")
  
  (define_insn_and_split "*addsi3_5200"
!   [(set (match_operand:SI 0 "nonimmediate_operand"         "=mr,mr,m,r,  ?a,?a,?a,?a")
! 	(plus:SI (match_operand:SI 1 "general_operand"     "%0, 0, 0,0,   a, a, r, a")
! 		 (match_operand:SI 2 "general_src_operand" " I, L, d,mrKi,Cj,r, a, J")))]
    "TARGET_COLDFIRE"
  {
    switch (which_alternative)
      {
--- 2323,2333 ----
    "! TARGET_COLDFIRE"
    "* return output_addsi3 (operands);")
  
  (define_insn_and_split "*addsi3_5200"
!   [(set (match_operand:SI 0 "nonimmediate_operand"         "=mr,mr,?a, m,r,  ?a,?a,?a")
! 	(plus:SI (match_operand:SI 1 "general_operand"     "%0, 0, a,0,0,   a, a, r")
! 		 (match_operand:SI 2 "general_src_operand" " I, L, J,d,mrKi,Cj,r, a")))]
    "TARGET_COLDFIRE"
  {
    switch (which_alternative)
      {
***************
*** 2338,2360 ****
        operands[2] = GEN_INT (- INTVAL (operands[2]));
        return "subq%.l %2,%0";
  
      case 2:
      case 3:
        return "add%.l %2,%0";
  
!     case 4:
        /* move%.l %2,%0\n\tadd%.l %1,%0 */
        return "#";
  
!     case 5:
        return MOTOROLA ? "lea (%1,%2.l),%0" : "lea %1@(0,%2:l),%0";
  
!     case 6:
        return MOTOROLA ? "lea (%2,%1.l),%0" : "lea %2@(0,%1:l),%0";
  
-     case 7:
-       return MOTOROLA ? "lea (%c2,%1),%0" : "lea %1@(%c2),%0";
  
      default:
        gcc_unreachable ();
        return "";
--- 2338,2361 ----
        operands[2] = GEN_INT (- INTVAL (operands[2]));
        return "subq%.l %2,%0";
  
      case 2:
+       return MOTOROLA ? "lea (%c2,%1),%0" : "lea %1@(%c2),%0";
+ 
      case 3:
+     case 4:
        return "add%.l %2,%0";
  
!     case 5:
        /* move%.l %2,%0\n\tadd%.l %1,%0 */
        return "#";
  
!     case 6:
        return MOTOROLA ? "lea (%1,%2.l),%0" : "lea %1@(0,%2:l),%0";
  
!     case 7:
        return MOTOROLA ? "lea (%2,%1.l),%0" : "lea %2@(0,%1:l),%0";
  
  
      default:
        gcc_unreachable ();
        return "";