Re: [PATCH] Fold (a > 0 ? 1.0 : -1.0) into copysign (1.0, a) and a * copysign (1.0, a) into abs(a)

[Marc Glisse <marc.glisse@inria.fr>]

+(for cmp (gt ge lt le)
+     outp (convert convert negate negate)
+     outn (negate negate convert convert)
+ /* Transform (X > 0.0 ? 1.0 : -1.0) into copysign(1, X). */
+ /* Transform (X >= 0.0 ? 1.0 : -1.0) into copysign(1, X). */
+ /* Transform (X < 0.0 ? 1.0 : -1.0) into copysign(1,-X). */
+ /* Transform (X <= 0.0 ? 1.0 : -1.0) into copysign(1,-X). */
+ (simplify
+  (cond (cmp @0 real_zerop) real_onep real_minus_onep)
+  (if (!HONOR_NANS (type) && !HONOR_SIGNED_ZEROS (type)
+       && types_match (type, TREE_TYPE (@0)))
+   (switch
+    (if (types_match (type, float_type_node))
+     (BUILT_IN_COPYSIGNF { build_one_cst (type); } (outp @0)))
+    (if (types_match (type, double_type_node))
+     (BUILT_IN_COPYSIGN { build_one_cst (type); } (outp @0)))
+    (if (types_match (type, long_double_type_node))
+     (BUILT_IN_COPYSIGNL { build_one_cst (type); } (outp @0))))))

There is already a 1.0 of the right type in the input, it would be easier 
to reuse it in the output than build a new one.

Non-generic builtins like copysign are such a pain... We also end up 
missing the 128-bit case that way (pre-existing problem, not your patch). 
We seem to have a corresponding internal function, but apparently it is 
not used until expansion (well, maybe during vectorization).

+ /* Transform (X > 0.0 ? -1.0 : 1.0) into copysign(1,-X). */
+ /* Transform (X >= 0.0 ? -1.0 : 1.0) into copysign(1,-X). */
+ /* Transform (X < 0.0 ? -1.0 : 1.0) into copysign(1,X). */
+ /* Transform (X <= 0.0 ? -1.0 : 1.0) into copysign(1,X). */
+ (simplify
+  (cond (cmp @0 real_zerop) real_minus_onep real_onep)
+  (if (!HONOR_NANS (type) && !HONOR_SIGNED_ZEROS (type)
+       && types_match (type, TREE_TYPE (@0)))
+   (switch
+    (if (types_match (type, float_type_node))
+     (BUILT_IN_COPYSIGNF { build_one_cst (type); } (outn @0)))
+    (if (types_match (type, double_type_node))
+     (BUILT_IN_COPYSIGN { build_one_cst (type); } (outn @0)))
+    (if (types_match (type, long_double_type_node))
+     (BUILT_IN_COPYSIGNL { build_one_cst (type); } (outn @0)))))))
+
+/* Transform X * copysign (1.0, X) into abs(X). */
+(simplify
+ (mult:c @0 (COPYSIGN real_onep @0))
+ (if (!HONOR_NANS (type) && !HONOR_SIGNED_ZEROS (type))
+  (abs @0)))

I would have expected it do to the right thing for signed zero and qNaN. 
Can you describe a case where it would give the wrong result, or are the 
conditions just conservative?

+/* Transform X * copysign (1.0, -X) into -abs(X). */
+(simplify
+ (mult:c @0 (COPYSIGN real_onep (negate @0)))
+ (if (!HONOR_NANS (type) && !HONOR_SIGNED_ZEROS (type))
+  (negate (abs @0))))
+
+/* Transform copysign (-1.0, X) into copysign (1.0, X). */
+(simplify
+ (COPYSIGN real_minus_onep @0)
+ (COPYSIGN { build_one_cst (type); } @0))

(simplify
  (COPYSIGN REAL_CST@0 @1)
  (if (REAL_VALUE_NEGATIVE (TREE_REAL_CST (@0)))
   (COPYSIGN (negate @0) @1)))
? Or does that create trouble with sNaN and only the 1.0 case is worth
the trouble?

-- 
Marc Glisse