optimization/6537: For -O (but not -O2 or -O0) incorrect assembly is generated

optimization/6537: For -O (but not -O2 or -O0) incorrect assembly is generated

[mflaster]

>Number:         6537
>Category:       optimization
>Synopsis:       For -O (but not -O2 or -O0) incorrect assembly is generated
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed May 01 12:56:01 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     Michael Flaster
>Release:        gcc version 2.95.3 20010315 (release)
>Organization:
>Environment:
FreeBSD 4.4-RELEASE #0
>Description:
When compiling the gzip compression library (zlib), some incorrect assembler seems to be generated.  Here is a snipped from the .c source:
line 201: f = q - c->sub.copy.dist;
      
      while (f < s->window) {            
        
        f += s->end - s->window;       
      }

Here is the generated .s:
.stabn 68,0,203,.LM75-inflate_codes
.LM75:
        movl 8(%ebp),%edx
        cmpl 40(%edx),%eax
' Compare s->window (40(%edx)) with f
        jae .L107
        movl 40(%edx),%eax
' Move s->window eax
        movl %edx,%ecx
' ? Curious
        movl 44(%ecx),%edx
' Move s->end to edx
        subl %eax,%edx
' Sub and put result in edx
        movl 40(%edx),%eax
' ??? Dereference the difference.  It seems to be trying to put s->window back in eax - except that edx no longer has a pointer to s.

I am attaching the compressed .i file.  The output of the compile line is:
nstg24:~/lucent/ews/zlib-1.1.4> cc -v -save-temps -g -O -DNO_DEFLATE -D_REENTRANT -c -o infcodes.o infcodes.c
Using builtin specs.
gcc version 2.95.3 20010315 (release) [FreeBSD]
 /usr/libexec/cpp0 -lang-c -v -D__GNUC__=2 -D__GNUC_MINOR__=95 -Di386 -D__FreeBSD__=4 -D__FreeBSD_cc_version=440000 -Dunix -D__i386__ -D__FreeBSD__=4 -D__FreeBSD_cc_version=440000 -D__unix__ -D__i386 -D__unix -Acpu(i386) -Amachine(i386) -Asystem(unix) -Asystem(FreeBSD) -D__OPTIMIZE__ -g -Acpu(i386) -Amachine(i386) -Di386 -D__i386 -D__i386__ -D__ELF__ -DNO_DEFLATE -D_REENTRANT infcodes.c infcodes.i
GNU CPP version 2.95.3 20010315 (release) [FreeBSD] (i386 FreeBSD/ELF)
#include "..." search starts here:
#include <...> search starts here:
 /usr/include
 /usr/include
End of search list.
The following default directories have been omitted from the search path:
 /usr/include/g++
End of omitted list.
 /usr/libexec/cc1 infcodes.i -quiet -dumpbase infcodes.c -g -O -version -o infcodes.s
GNU C version 2.95.3 20010315 (release) [FreeBSD] (i386-unknown-freebsd) compiled by GNU C version 2.95.3 20010315 (release) [FreeBSD].
 /usr/libexec/elf/as -v -o infcodes.o infcodes.s
GNU assembler version 2.11.2 20010719 [FreeBSD] (i386-unknown-freebsd4) using BFD version 2.11.2 20010719 [FreeBSD]


I've tried this on other FreeBSD machines in our lab, some running gcc 2.95.2, some running 3.0.4, and I seem to get the exact same problem.  Adding printf's near the source lines in question, or changing the optimization level, makes the problem go away.

Thanks in advance!

Michael Flaster
>How-To-Repeat:

>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:
----gnatsweb-attachment----
Content-Type: application/x-gzip-compressed; name="infcodes.i.gz"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="infcodes.i.gz"
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Re: optimization/6537: For -O (but not -O2 or -O0) incorrect assembly is generated

[ebotcazou]

Synopsis: For -O (but not -O2 or -O0) incorrect assembly is generated

State-Changed-From-To: open->feedback
State-Changed-By: ebotcazou
State-Changed-When: Wed Feb 19 10:48:35 2003
State-Changed-Why:
    Confirmed with gcc 2.95.3, but the assembly output looks
    correct with gcc 3.0.4 and later versions.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=6537