optimization/10312: optimizer creates wrong code for loop

[p.van-hoof@qub.ac.uk]

>Number:         10312
>Category:       optimization
>Synopsis:       optimizer creates wrong code for loop
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Fri Apr 04 18:56:00 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator:     Peter van Hoof
>Release:        3.4 20030403 (experimental)
>Organization:
Queen's University of Belfast
>Environment:
System: SunOS scooby 5.9 Generic_112233-04 sun4u sparc SUNW,Sun-Blade-100
Architecture: sun4

	
host: sparc-sun-solaris2.9
build: sparc-sun-solaris2.9
target: sparc-sun-solaris2.9
configured with: /scratch/gcc-repository/cvs/gcc/configure --prefix=/opt/local/gcc340 --enable-languages=c,c++,f77 --with-gnu-as --with-as=/opt/local/bin/gas
>Description:
The optimizer creates wrong code for the loop in the attached program.
When compiled with -O2, the resulting code will generate a segfault.
If the "double a" member of the struct is removed, the program will get
stuck in an infinite loop, rather than crash.

The program behaves correctly with gcc 3.2.2 and 3.3, so this is a regression.
>How-To-Repeat:
scooby> gcc -v -O2 c.c
Reading specs from /opt/local/gcc340/lib/gcc-lib/sparc-sun-solaris2.9/3.4/specs
Configured with: /scratch/gcc-repository/cvs/gcc/configure --prefix=/opt/local/gcc340 --enable-languages=c,c++,f77 --with-gnu-as --with-as=/opt/local/bin/gas
Thread model: posix
gcc version 3.4 20030403 (experimental)
 /opt/local/gcc340/lib/gcc-lib/sparc-sun-solaris2.9/3.4/cc1 -quiet -v -Dsparc -D__sparc__ -D__sparc -D__GCC_NEW_VARARGS__ -Acpu=sparc -Amachine=sparc c.c -quiet -dumpbase c.c -auxbase c -O2 -version -o /var/tmp//ccXLgTFq.s
ignoring nonexistent directory "/opt/local/gcc340/sparc-sun-solaris2.9/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /opt/local/gcc340/include
 /opt/local/gcc340/lib/gcc-lib/sparc-sun-solaris2.9/3.4/include
 /usr/include
End of search list.
GNU C version 3.4 20030403 (experimental) (sparc-sun-solaris2.9)
	compiled by GNU C version 3.4 20030403 (experimental).
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
 /opt/local/bin/gas -V -Qy -s -o /var/tmp//ccOfg7jT.o /var/tmp//ccXLgTFq.s
GNU assembler version 2.13.2.1 (sparc-sun-solaris2.9) using BFD version 2.13.2.1
 /opt/local/gcc340/lib/gcc-lib/sparc-sun-solaris2.9/3.4/collect2 -V -Y P,/usr/ccs/lib:/usr/lib -Qy /opt/local/gcc340/lib/gcc-lib/sparc-sun-solaris2.9/3.4/crt1.o /opt/local/gcc340/lib/gcc-lib/sparc-sun-solaris2.9/3.4/crti.o /usr/ccs/lib/values-Xa.o /opt/local/gcc340/lib/gcc-lib/sparc-sun-solaris2.9/3.4/crtbegin.o -L/opt/local/gcc340/lib/gcc-lib/sparc-sun-solaris2.9/3.4 -L/usr/ccs/bin -L/usr/ccs/lib -L/opt/local/gcc340/lib/gcc-lib/sparc-sun-solaris2.9/3.4/../../.. /var/tmp//ccOfg7jT.o -lgcc -lgcc_eh -lc -lgcc -lgcc_eh -lc /opt/local/gcc340/lib/gcc-lib/sparc-sun-solaris2.9/3.4/crtend.o /opt/local/gcc340/lib/gcc-lib/sparc-sun-solaris2.9/3.4/crtn.o
ld: Software Generation Utilities - Solaris Link Editors: 5.9-1.373

scooby>	a.out 
Segmentation fault

scooby>	cat c.c
struct {
	double a; 
	int n[2];
} g = { 0., { 1, 2 } };

int k = 0;

void b(int *j) {}

int main()
{
	int j;
	for( j=0; j < 2; j++ )
		k = ( k > g.n[j] ) ? k : g.n[j];
	k++;
	b(&j);
	return 0;
}
>Fix:
Workaround: use lower level of optimization.
>Release-Note:
>Audit-Trail:
>Unformatted: