Hello,

this patch lets us fold a bit_field_ref of a constructor even when the 
elements are vectors. Writing a testcase is not that convenient because of 
the lack of a dead code elimination pass after forwprop4 (RTL doesn't 
always remove everything either), but I see a clear difference on this 
test on x86_64 without AVX.

typedef double vec __attribute__((vector_size(4*sizeof(double))));
void f(vec*x){
   *x+=*x+*x;
}
double g(vec*x){
   return (*x+*x)[3];
}
void h(vec*x, double a, double b, double c, double d){
   vec y={a,b,c,d};
   *x+=y;
}


I don't know if the patch (assuming it is ok) is suitable for stage 3, it 
may have to wait. It passes bootstrap+testsuite.

I am still not quite sure why we even have a valid_gimple_rhs_p function 
(after which we usually give up if it says no) instead of gimplifying, so 
I may have missed a reason why CONSTRUCTOR or BIT_FIELD_REF shouldn't be 
ok.


2012-11-12  Marc Glisse  <marc.glisse@inria.fr>

 	* fold-const.c (fold_ternary_loc) [BIT_FIELD_REF]: Handle
 	CONSTRUCTOR with vector elements.
 	* tree-ssa-propagate.c (valid_gimple_rhs_p): Handle CONSTRUCTOR
 	and BIT_FIELD_REF.

-- 
Marc Glisse