Noticed through inspection.

% cat cbev.ll
define <4 x i32> %foo(<4 x i32> %a, <4 x i32> %b) {
  %c = sub <4 x i32> %a, %b
  %d = add <4 x i32> %b, %c
  %e = mul <4 x i32> %c, %d
;  %f = udiv <4 x i32> %d, %e   ; Fails an assertion in CBackend.cpp
;  %g = sdiv <4 x i32> %e, %f   ; Same
  ret <4 x i32> %e
}
% llvm-as -o cbev.bc cbev.ll
% llc -march=c -o cbev.c cbev.bc
% tail -n 7 cbev.c
unsigned int foo(unsigned int ltmp_0_1[4], unsigned int ltmp_1_1[4])[4] {
  unsigned int ltmp_2_1[4];

  ltmp_2_1 = ltmp_0_1 - ltmp_1_1;
  return (ltmp_2_1*(ltmp_1_1 + ltmp_2_1));
}

% gcc -o cbev.o -c cbev.c
cbev.c:106: error: ‘foo’ declared as function returning an array
cbev.c:107: warning: conflicting types for built-in function ‘malloc’
cbev.c:129: error: ‘foo’ declared as function returning an array
cbev.c: In function ‘foo’:
cbev.c:132: error: incompatible types in assignment
cbev.c:133: error: invalid operands to binary +

An error message, inserting a vector lowering pass before the CBE, or fixing the codegen would all be 
improvements.

Emitting Altivec 'vector' types instead of arrays would make fixing the codegen relatively easy when 
targetting PowerPC, since Altivec provides operator overloads for vector ops.