On Thu, Oct 19, 2017 at 08:03:45PM -0600, Sandra Loosemore wrote:
A harder problem is that doing the high/lo_sum splitting in expand
inhibits subsequent optimizations. One such problem arises when you
have accesses to multiple fields in a static structure object. Expand
sees this as many (symbol + offset) expressions involving the same
symbol with different constant offsets. What we should be doing in
that case is CSE'ing the symbol address computation rather than
splitting every such expression individually.
Do you have the needed relocations for that though?
If not, then you need to do:
tmp = high (symbol);
tmp |= lo_sum (symbol); // or +
a = [tmp + 0];
b = [tmp + 4];
c = [tmp + 8];
if you do (like e.g. sparc64 has the %olo relocation), then you can do
tmp = high (symbol);
a = [tmp + lo_sum (symbol) + 0];
b = [tmp + lo_sum (symbol) + 4];
c = [tmp + lo_sum (symbol) + 8];
If you tried to do:
tmp = high (symbol);
a = [tmp + lo_sum (symbol)];
b = [tmp + lo_sum (symbol + 4)];
c = [tmp + lo_sum (symbol + 8)];
then this would break if lo_sum (symbol + 4) or lo_sum (symbol + 8)
is < 4.