c/4950: gcc-3.0.2 unsigned char *pb++ produces double increment

c/4950: gcc-3.0.2 unsigned char *pb++ produces double increment

[Dennis Altrogge]

>Number:         4950
>Category:       c
>Synopsis:       gcc-3.0.2 unsigned char *pb++ does double increment
>Confidential:   no
>Severity:       critical
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Mon Nov 26 14:26:00 PST 2001
>Closed-Date:
>Last-Modified:
>Originator:     Dennis Altrogge
>Release:        3.0.2
>Organization:
Nortel Networks 
>Environment:
System: SunOS farside 5.6 Generic_105181-25 sun4m sparc SUNW,SPARCstation-20
Architecture: sun4

	
host: sparc-sun-solaris2.6
build: sparc-sun-solaris2.6
target: m68k-unknown-elf
configured with: ../gcc-3.0.2/configure --target=m68k-elf --with-newlib --prefix=/engwest/agt_tools/compilers/gcc/3.0.2-sol26-m68k-elf
>Description:
Compile the following C code with gcc-3.0.2 m68k-elf.
Use objdump to examine the .o file.
	
>How-To-Repeat:
	

############ screen output ##############

/engwest/agt_tools/compilers/gcc/3.0.2-sol26-m68k-elf/bin/m68k-elf-gcc -c -g -O -funsigned-char -fno-builtin -Wall -v -save-temps  \
	-m5200 -Wa,-register-prefix-optional bug2.c

####### produced ################3

Reading specs from /engwest/agt_tools/compilers/gcc/3.0.2-sol26-m68k-elf/lib/gcc-lib/m68k-elf/3.0.2/specs
Configured with: ../gcc-3.0.2/configure --target=m68k-elf --with-newlib --prefix=/engwest/agt_tools/compilers/gcc/3.0.2-sol26-m68k-elf
Thread model: single
gcc version 3.0.2
 /engwest/agt_tools/compilers/gcc/3.0.2-sol26-m68k-elf/lib/gcc-lib/m68k-elf/3.0.2/cpp0 -lang-c -v -D__GNUC__=3 -D__GNUC_MINOR__=0 -D__GNUC_PATCHLEVEL__=2 -Dmc68000 -D__embedded__ -D__mc68000__ -D__embedded__ -D__mc68000 -Asystem=embedded -Amachine=mc68000 -D__CHAR_UNSIGNED__ -D__OPTIMIZE__ -D__STDC_HOSTED__=1 -Wall -Dmcf5200 -D__mcf5200__ -D__mcf5200 bug2.c bug2.i
GNU CPP version 3.0.2 (cpplib) (68k, MIT syntax)
ignoring nonexistent directory "/engwest/agt_tools/compilers/gcc/3.0.2-sol26-m68k-elf/m68k-elf/sys-include"
#include "..." search starts here:
#include <...> search starts here:
 /engwest/agt_tools/compilers/gcc/3.0.2-sol26-m68k-elf/lib/gcc-lib/m68k-elf/3.0.2/include
 /engwest/agt_tools/compilers/gcc/3.0.2-sol26-m68k-elf/m68k-elf/include
End of search list.
 /engwest/agt_tools/compilers/gcc/3.0.2-sol26-m68k-elf/lib/gcc-lib/m68k-elf/3.0.2/cc1 -fpreprocessed bug2.i -quiet -dumpbase bug2.c -m5200 -g -O -Wall -version -funsigned-char -fno-builtin -o bug2.s
GNU CPP version 3.0.2 (cpplib) (68k, MIT syntax)
GNU C version 3.0.2 (m68k-elf)
        compiled by GNU C version 2.95.2 19991024 (release).
 /engwest/agt_tools/compilers/gcc/3.0.2-sol26-m68k-elf/lib/gcc-lib/m68k-elf/3.0.2/../../../../m68k-elf/bin/as -m5200 -register-prefix-optional -o bug2.o bug2.s


/* ############## the bad C code gcc-3.0.2 (2.95.3 works)################## */

unsigned int   er_F33BProgram(
                        unsigned int    d_AdrLo,
                                 unsigned int    d_AdrHi,
                                 void     *pv_Data
                                 )
{
   unsigned char     *pb_Data, b_Data;

   pb_Data = pv_Data;

   do
   {
/*GNU3.0.2 with binutil2.11.2 produced moveb %a1@+,%d2 2X! for pb_Data++ */

      b_Data = *pb_Data++ & *(volatile unsigned char*)d_AdrLo;

      *(volatile unsigned char*)d_AdrLo = b_Data;

      d_AdrLo += sizeof( unsigned char );

   } while( d_AdrLo < d_AdrHi );

   return   0;

}


/* ################### the bug2.i file ########################## */

#if 0

# 1 "bug2.c"
unsigned int er_F33BProgram(
                        unsigned int d_AdrLo,
                                 unsigned int d_AdrHi,
                                 void *pv_Data
                                 )
{
   unsigned char *pb_Data, b_Data;

   pb_Data = pv_Data;

   do
   {


      b_Data = *pb_Data++ & *(volatile unsigned char*)d_AdrLo;

      *(volatile unsigned char*)d_AdrLo = b_Data;

      d_AdrLo += sizeof( unsigned char );

   } while( d_AdrLo < d_AdrHi );

   return 0;

}

#endif

/* #################### objdump of bug2.o ############################ */
#if 0
/* produced this */


bug2.o:     file format elf32-m68k

Disassembly of section .text:

00000000 <er_F33BProgram>:
   0:	4e56 0000      	linkw %fp,#0
   4:	2f02           	movel %d2,%sp@-
   6:	206e 0008      	moveal %fp@(8),%a0
   a:	222e 000c      	movel %fp@(12),%d1
   e:	226e 0010      	moveal %fp@(16),%a1
  12:	1010           	moveb %a0@,%d0
/* ######### here is the bug: note BYTE *pb_Data++ produces 2X incs */
  14:	1419           	moveb %a1@+,%d2
  16:	1419           	moveb %a1@+,%d2
  18:	c082           	andl %d2,%d0
/* gcc-2.95.3 optimized the next 2 instructions to:  10c0  moveb %d0,%a0@+ */
  1a:	1080           	moveb %d0,%a0@
  1c:	5288           	addql #1,%a0
  1e:	b288           	cmpl %a0,%d1
  20:	62f0           	bhis 12 <er_F33BProgram+0x12>
  22:	4280           	clrl %d0
  24:	241f           	movel %sp@+,%d2
  26:	4e5e           	unlk %fp
  28:	4e75           	rts
        ...
#endif
>Fix:
No known fix.
	
>Release-Note:
>Audit-Trail:
>Unformatted: