[PATCH] Fix ldist memset discovery with -0.0 (PR tree-optimization/72824)

[Jakub Jelinek]

Hi!

Only +0.0 stores can be optimized into memset, -0.0 can't, so if we are
honoring signed zeros, we should make sure the constant is positive.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2016-08-08  Jakub Jelinek  <ja...@redhat.com>

        PR tree-optimization/72824
        * tree-loop-distribution.c (const_with_all_bytes_same): If honoring
        signed zeros, verify real_zerop is not negative.

        * gcc.c-torture/execute/ieee/pr72824.c: New test.

--- gcc/tree-loop-distribution.c.jj     2016-07-16 10:41:04.000000000 +0200
+++ gcc/tree-loop-distribution.c        2016-08-07 13:55:19.704681784 +0200
@@ -750,12 +750,40 @@ const_with_all_bytes_same (tree val)
   int i, len;
 
   if (integer_zerop (val)
-      || real_zerop (val)
       || (TREE_CODE (val) == CONSTRUCTOR
           && !TREE_CLOBBER_P (val)
           && CONSTRUCTOR_NELTS (val) == 0))
     return 0;
 
+  if (real_zerop (val))
+    {
+      if (!HONOR_SIGNED_ZEROS (val))
+       return 0;
+      /* If honoring signed zeros, only return 0 for +0.0, not for -0.0.  */
+      switch (TREE_CODE (val))
+       {
+       case REAL_CST:
+         if (!real_isneg (TREE_REAL_CST_PTR (val)))
+           return 0;
+         break;
+       case COMPLEX_CST:
+         if (!const_with_all_bytes_same (TREE_REALPART (val))
+             && !const_with_all_bytes_same (TREE_IMAGPART (val)))
+           return 0;
+         break;
+       case VECTOR_CST:
+         unsigned int j;
+         for (j = 0; j < VECTOR_CST_NELTS (val); ++j)
+           if (const_with_all_bytes_same (val))
+             break;
+         if (j == VECTOR_CST_NELTS (val))
+           return 0;
+         break;
+       default:
+         break;
+       }
+    }
+
   if (CHAR_BIT != 8 || BITS_PER_UNIT != 8)
     return -1;
 
--- gcc/testsuite/gcc.c-torture/execute/ieee/pr72824.c.jj       2016-08-07 
13:19:42.443863775 +0200
+++ gcc/testsuite/gcc.c-torture/execute/ieee/pr72824.c  2016-08-07 
13:19:35.034958218 +0200
@@ -0,0 +1,19 @@
+/* PR tree-optimization/72824 */
+
+static inline void
+foo (float *x, float value)
+{
+  int i;
+  for (i = 0; i < 32; ++i)
+    x[i] = value;
+}
+
+int
+main ()
+{
+  float x[32];
+  foo (x, -0.f);
+  if (__builtin_copysignf (1.0, x[3]) != -1.0f)
+    __builtin_abort ();
+  return 0;
+}

        Jakub