[Bug target/19684] New: avr-gcc 4.0 (and 3.3.4): wrong size in asm comment

[Bug target/19684] New: avr-gcc 4.0 (and 3.3.4): wrong size in asm comment

[dmixm at marine dot febras dot ru]

Comment about function `foo' size: 
 
  27                    /* function foo size 10 (9) */ 
 
show wrong value. (Compare it with next function.) 
 
Compiler: avr-gcc (GCC) 4.0.0 20050109 (experimental) 
Options:  -W -Wall -Os -Wa,-ahl 
 
The same error (for `foo') in 3.3.4 . 
 
Certainly, it is nonsense. But, maybe, this display 
of more serious mistake? 
 
Program: 
~~~~~~~~ 
int foo (int x) 
{ 
    int i; 
    for (i= 10; i; i--) 
        x *= 2; 
    return x; 
} 
 
int foo_with_true_size (int x) 
{ 
    x += 100; 
    do { 
        x *= 2; 
    } while (x > 0); 
    return x; 
} 
 
Listing: 
~~~~~~~~ 
GAS LISTING /tmp/ccJGSrye.s                     page 1 
 
 
   1                            .file   "foo.c" 
   2                            .arch avr2 
   3                    __SREG__ = 0x3f 
   4                    __SP_H__ = 0x3e 
   5                    __SP_L__ = 0x3d 
   6                    __tmp_reg__ = 0 
   7                    __zero_reg__ = 1 
   8                            .global __do_copy_data 
   9                            .global __do_clear_bss 
  10                            .text 
  11                    .global foo 
  12                            .type   foo, @function 
  13                    foo: 
  14                    /* prologue: frame size=0 */ 
  15                    /* prologue end (size=0) */ 
  16 0000 2AE0                  ldi r18,lo8(10) 
  17 0002 30E0                  ldi r19,hi8(10) 
  18                    .L2: 
  19 0004 880F                  add r24,r24 
  20 0006 991F                  adc r25,r25 
  21 0008 2150                  subi r18,lo8(-(-1)) 
  22 000a 3040                  sbci r19,hi8(-(-1)) 
  23 000c D9F7                  brne .L2 
  24                    /* epilogue: frame size=0 */ 
  25 000e 0895                  ret 
  26                    /* epilogue end (size=1) */ 
  27                    /* function foo size 10 (9) */ 
  28                            .size   foo, .-foo 
  29                    .global foo_with_true_size 
  30                            .type   foo_with_true_size, @function 
  31                    foo_with_true_size: 
  32                    /* prologue: frame size=0 */ 
  33                    /* prologue end (size=0) */ 
  34 0010 8C59                  subi r24,lo8(-(100)) 
  35 0012 9F4F                  sbci r25,hi8(-(100)) 
  36                    .L8: 
  37 0014 880F                  add r24,r24 
  38 0016 991F                  adc r25,r25 
  39 0018 1816                  cp __zero_reg__,r24 
  40 001a 1906                  cpc __zero_reg__,r25 
  41 001c DCF3                  brlt .L8 
  42                    /* epilogue: frame size=0 */ 
  43 001e 0895                  ret 
  44                    /* epilogue end (size=1) */ 
  45                    /* function foo_with_true_size size 8 (7) */ 
  46                            .size   foo_with_true_size, .-foo_with_true_size 
  47                    /* File "foo.c": code   18 = 0x0012 (  16), prologues 
0, epilogues   2 */

-- 
           Summary: avr-gcc 4.0 (and 3.3.4): wrong size in asm comment
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: dmixm at marine dot febras dot ru
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19684

[Bug target/19684] avr-gcc 4.0 (and 3.3.4): wrong size in asm comment

[ericw at evcohs dot com]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ericw at evcohs dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19684

[Bug target/19684] avr-gcc 4.0 (and 3.3.4): wrong size in asm comment

[berndtrog at yahoo dot com]

------- Additional Comments From berndtrog at yahoo dot com  2005-03-02 22:44 -------
I can confirm this for gcc-4.0.0-20050228


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19684

[Bug target/19684] avr-gcc 4.0 (and 3.3.4): wrong size in asm comment

[andrewhutchinson at cox dot net]

------- Additional Comments From andrewhutchinson at cox dot net  2005-03-03 01:57 -------
This is almost certainly caused by code peepholes doing last minute optimisation
of the code just before the assembler is generated. 

Prior to that, all RTL instructions have a length (in 16 bit words) that is
*soley* used to select the appropriate jump and branch instructions. The size
comments are generated from those lengths. If a peephole does indeed change some
instructions, they will quite likely over estimate the final size (as is the
case presented here)

The length (and so size) is fine if it over estimates the actual size
(Jumps/branches can always work over shorter distances.) The actual jump
displacments are based on labels so they are unaffected.

There may be some other areas of the backend that apply worse-case estimates of
asm instruction size to avoid the complexity of calculating every situation.
However, peepholes definitely do this!

I would suggest this is a non-bug as the size is an internal compiler debug
comment and there is no regression, misoptimisation  or similar downside.

If the size ever under-estimates the true size THAT IS A BUG!




-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19684

[Bug target/19684] avr-gcc 4.0 (and 3.3.4): wrong size in asm comment (peephole)

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-03-10 14:20 -------
Also note peepholes should really be changed to peephole2.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2005-03-10 14:20:10
               date|                            |
            Summary|avr-gcc 4.0 (and 3.3.4):    |avr-gcc 4.0 (and 3.3.4):
                   |wrong size in asm comment   |wrong size in asm comment
                   |                            |(peephole)


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19684