[Bug optimization/11683] New: SH Optimizer creates incorrect code

[schwartz_m_ at hotmail dot com]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11683

           Summary: SH Optimizer creates incorrect code
           Product: gcc
           Version: 3.2.2
            Status: UNCONFIRMED
          Severity: critical
          Priority: P1
         Component: optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: schwartz_m_ at hotmail dot com
                CC: gcc-bugs at gcc dot gnu dot org,schwartz_m_ at hotmail
                    dot com
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: sh-hitachi-hms

The following is an example of how the SH4 optimizer creates incorrect 
optimized code which results in a memory overrun. The bug is recreated using 
the following simple program:

------------------------ bug.cc -----------------------------

void bar( int x );

int foo( void )
{
  int x[50];
  int y, z;

  while( true ) {
    asm volatile( " \n" : : : "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", 
		  "r8", "r9", "r10", "r11", "r12", "r13" );
    y -= z;
    bar( y );
  }
}

-------------------- Compiler command -----------------------

sh-hitachi-hms-gcc -g "-Wa,-ahl" -Wall -ansi -m4-nofpu -O2 -fno-common -pipe -
fcheck-new -fmessage-length=0 -Wno-non-template-friend -fno-exceptions -fno-
rtti -c -o bug.o bug.cc -save-temps -v > bug.lst

-------------------- Compiler output (with -v) --------------

sh-hitachi-hms-gcc: warning: -pipe ignored because -save-temps specified
Reading specs from /home/users/gnu/gcc-3.2.2/installation/sh/lib/gcc-lib/sh-
hitachi-hms/3.2.2/specs
Configured with: ../gcc-3.2.2/configure --target=sh-hitachi-hms --
prefix=/home/users/gnu/gcc-3.2.2/installation/sh --with-gnu-as --with-gnu-ld --
with-headers=/home/users/gnu/gcc-3.2.2/include/madan-orig --enable-
languages=c,c++
Thread model: single
gcc version 3.2.2
 /home/users/gnu/gcc-3.2.2/installation/sh/lib/gcc-lib/sh-hitachi-
hms/3.2.2/cpp0 -lang-c++ -D__GNUG__=3 -D__DEPRECATED -D__STRICT_ANSI__ -
trigraphs -$ -v -D__GNUC__=3 -D__GNUC_MINOR__=2 -D__GNUC_PATCHLEVEL__=2 -
D__GXX_ABI_VERSION=102 -D__sh__ -Acpu=sh -Amachine=sh -D__OPTIMIZE__ -
D__STDC_HOSTED__=1 -D__sh3__ -D__SH4_NOFPU__ -D__SIZE_TYPE__=unsigned int -
D__PTRDIFF_TYPE__=int bug.cc -Wall -Wno-non-template-friend bug.ii
GNU CPP version 3.2.2 (cpplib) (Hitachi SH)
ignoring nonexistent directory "/home/users/gnu/gcc-3.2.2/installation/sh/sh-
hitachi-hms/include"
#include "..." search starts here:
#include <...> search starts here:
 /home/users/gnu/gcc-3.2.2/installation/sh/include/c++/3.2.2
 /home/users/gnu/gcc-3.2.2/installation/sh/include/c++/3.2.2/sh-hitachi-hms
 /home/users/gnu/gcc-3.2.2/installation/sh/include/c++/3.2.2/backward
 /home/users/gnu/gcc-3.2.2/installation/sh/include
 /home/users/gnu/gcc-3.2.2/installation/sh/lib/gcc-lib/sh-hitachi-
hms/3.2.2/include
 /home/users/gnu/gcc-3.2.2/installation/sh/sh-hitachi-hms/sys-include
End of search list.
 /home/users/gnu/gcc-3.2.2/installation/sh/lib/gcc-lib/sh-hitachi-
hms/3.2.2/cc1plus -fpreprocessed bug.ii -trigraphs -$ -quiet -dumpbase bug.cc -
m4-nofpu -ansi -g -O2 -Wall -Wno-non-template-friend -ansi -version -fno-
common -fcheck-new -fmessage-length=0 -fno-exceptions -fno-rtti -o bug.s
GNU CPP version 3.2.2 (cpplib) (Hitachi SH)
GNU C++ version 3.2.2 (sh-hitachi-hms)
        compiled by GNU C version 3.2.2.
bug.cc: In function `int foo()':
bug.cc:5: warning: unused variable `int x[50]'
bug.cc:6: warning: `int y' might be used uninitialized in this function
bug.cc:6: warning: `int z' might be used uninitialized in this function
 /home/users/gnu/gcc-3.2.2/installation/sh/lib/gcc-lib/sh-hitachi-
hms/3.2.2/../../../../sh-hitachi-hms/bin/as -ahl -o bug.o bug.s

------------------------ bug.lst (partial) ------------------

  11:bug.cc        ****     y -= z;
  27              		.ln	8
  28 0016 900B     		mov.w	L6,r0
  29 0018 6103     		mov	r0,r1
  30 001a 31EC     		add	r14,r1
  31 001c 5213     		mov.l	@(12,r1),r2
  32 001e 5114     		mov.l	@(16,r1),r1
  33 0020 3218     		sub	r1,r2
  34 0022 1123     		mov.l	r2,@(12,r1)

  42              		.align 1
  43              	L6:
  44 0030 00BC     		.short	188

Note that in line 32, register r1 is clobbered, while in line 34 it is used as 
if it was not clobbered. This causes a memory overrun.

The following is also known about the bug:
1) It also happens in .c files.
2) It also happens with -O1. In fact, I couldn't find a specific optimization, 
which when removed, causes the bug to disappear.
3) This also happens in gcc 3.2.3.
4) The bug won't happen when the stack is used with less than 128 bytes.

Please adivse as to possible workarounds or patches.

Thanks,

Moshe Schwartz