optimization/10087: [3.3/3.4 regression] optimizer produces wrong code when indexing 2D array

[Steven Bosscher]

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=10087

# gcc-3.3 10087.c -O
# a.out
result 1.000000e+00
# gcc-3.3 10087.c -O -fforce-mem -fstrength-reduce -fgcse
# a.out
result -1.997810e+00

Turning off any of these three options makes the output equal to 
unoptimized or -O.

Greetz
Steven