[PATCH] match.pd: add single-use check for (x & y) ^ y -> ~x & y (PR85758)

[Alexander Monakov]

Hello,

I'd like to apply this to resolve PR 85758. In bug discussion Marc noted that
what we are doing leads to code with higher instruction-level parallelism,
but it also has higher register pressure and longer code if the target does
not expose and-not patterns.

Now that we have 2->2 combine, it is able to recover SSE and-not for 

typedef unsigned T __attribute__((vector_size(16)));

void g(T, T);

void f(T a, T b, T m, T s)
{
    m &= s;
    a += m;
    m ^= s;
    b += m;
    g(a, b);
}

but in scalar case costs say the original sequence is cheaper, even with
-mbmi. I think it's fine.

OK for trunk? If a testcase is needed, please tell how to implement it.

Alexander

        * match.pd ((X & Y) ^ Y): Add :s qualifier to inner operand.

diff --git a/gcc/match.pd b/gcc/match.pd
index cb3c93e3e16..d43e52d05cd 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -1027,7 +1027,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 (for opo (bit_and bit_xor)
      opi (bit_xor bit_and)
  (simplify
-  (opo:c (opi:c @0 @1) @1) 
+  (opo:c (opi:cs @0 @1) @1)
   (bit_and (bit_not @0) @1)))
 
 /* Given a bit-wise operation CODE applied to ARG0 and ARG1, see if both