On May 6, 2005, at 9:27 AM, chris jefferson wrote:
Michael Cieslinski wrote:
Consider the following short program:
#include <algorithm>
void Tst1(short* __restrict__ SrcP, short* __restrict__ MinP, int Len)
{
for (int x=0; x<Len; x++)
MinP[x] = SrcP[x] <? MinP[x];
}
void Tst2(short* __restrict__ SrcP, short* __restrict__ MinP, int Len)
{
for (int x=0; x<Len; x++)
MinP[x] = std::min(SrcP[x], MinP[x]);
}
If I compile it with gcc41 -O2 -ftree-vectorize -ftree-vectorizer-verbose=5 function Tst1 gets vectorized but Tst2 not.
The reason for this is <? results in a MIN_EXPR while std::min generates a
conditional code.
My question is, how can I get a MIN_EXPR without using the deprecated min <?
operator?
The problem with C++ is in fold as we now have to disable the optimization
which converted "a >= b ? b : a" to MIN_EXPR.
Try the following instead:
MinP[x] = (SrcP[x]<MinP[x]) ? (short)SrcP[x] : MinP[x];
which forces this to be an rvalue instead of the normal lvalue which should
allow fold to convert this to MIN_EXPR
-- Pinski
