GEPs with all zero indices are trivially coalesced by fast-isel. For example,

%arrayidx135 = getelementptr inbounds [4 x [4 x [4 x [4 x i32]]]]* %M0, i32 0, i64 0
%arrayidx136 = getelementptr inbounds [4 x [4 x [4 x i32]]]* %arrayidx135, i32 0, i64 %idxprom134

Prior to this commit, the GEP instruction that defines %arrayidx136 thought that 
%arrayidx135 was a trivial kill.  The GEP that defines %arrayidx135 doesn't 
generate any code and thus %M0 gets folded into the second GEP.  Thus, we need
to look through GEPs with all zero indices.
rdar://10443319

llvm-svn: 144730