Add support for conditional xorsign [PR96373]

This patch is an optimisation, but it's also a prerequisite for
fixing PR96373 without regressing vect-xorsign_exec.c.

Currently the vectoriser vectorises:

  for (i = 0; i < N; i++)
    r[i] = a[i] * __builtin_copysignf (1.0f, b[i]);

as two unconditional operations (copysign and mult).
tree-ssa-math-opts.cc later combines them into an "xorsign" function.
This works for both Advanced SIMD and SVE.

However, with the fix for PR96373, the vectoriser will instead
generate a conditional multiplication (IFN_COND_MUL).  Something then
needs to fold copysign & IFN_COND_MUL to the equivalent of a conditional
xorsign.  Three obvious options were:

(1) Extend tree-ssa-math-opts.cc.
(2) Do the fold in match.pd.
(3) Leave it to rtl combine.

I'm against (3), because this isn't a target-specific optimisation.
(1) would be possible, but would involve open-coding a lot of what
match.pd does for us.  And, in contrast to doing the current
tree-ssa-math-opts.cc optimisation in match.pd, there should be
no danger of (2) happening too early.  If we have an IFN_COND_MUL
then we're already past the stage of simplifying the original
source code.

There was also a choice between adding a conditional xorsign ifn
and simply open-coding the xorsign.  The latter seems simpler,
and means less boiler-plate for target-specific code.

The signed_or_unsigned_type_for change is needed to make sure
that we stay in "SVE space" when doing the optimisation on 128-bit
fixed-length SVE.

gcc/
	PR tree-optimization/96373
	* tree.h (sign_mask_for): Declare.
	* tree.cc (sign_mask_for): New function.
	(signed_or_unsigned_type_for): For vector types, try to use the
	related_int_vector_mode.
	* genmatch.cc (commutative_op): Handle conditional internal functions.
	* match.pd: Fold an IFN_COND_MUL+copysign into an IFN_COND_XOR+and.

gcc/testsuite/
	PR tree-optimization/96373
	* gcc.target/aarch64/sve/cond_xorsign_1.c: New test.
	* gcc.target/aarch64/sve/cond_xorsign_2.c: Likewise.

6 files changed, 114 insertions, 0 deletions

diff --git a/gcc/genmatch.cc b/gcc/genmatch.cc
index d4cb439..e147ab9 100644
--- a/gcc/genmatch.cc
+++ b/gcc/genmatch.cc
@@ -489,6 +489,21 @@ commutative_op (id_base *id)
       case CFN_FNMS:
 	return 0;
 
+      case CFN_COND_ADD:
+      case CFN_COND_MUL:
+      case CFN_COND_MIN:
+      case CFN_COND_MAX:
+      case CFN_COND_FMIN:
+      case CFN_COND_FMAX:
+      case CFN_COND_AND:
+      case CFN_COND_IOR:
+      case CFN_COND_XOR:
+      case CFN_COND_FMA:
+      case CFN_COND_FMS:
+      case CFN_COND_FNMA:
+      case CFN_COND_FNMS:
+	return 1;
+
       default:
 	return -1;
       }
diff --git a/gcc/match.pd b/gcc/match.pd
index 56ac743..f605b79 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -339,6 +339,20 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
  (if (REAL_VALUE_NEGATIVE (TREE_REAL_CST (@0)))
   (COPYSIGN_ALL (negate @0) @1)))
 
+/* Transform c ? x * copysign (1, y) : z to c ? x ^ signs(y) : z.
+   tree-ssa-math-opts.cc does the corresponding optimization for
+   unconditional multiplications (via xorsign).  */
+(simplify
+ (IFN_COND_MUL:c @0 @1 (IFN_COPYSIGN real_onep @2) @3)
+ (with { tree signs = sign_mask_for (type); }
+  (if (signs)
+   (with { tree inttype = TREE_TYPE (signs); }
+    (view_convert:type
+     (IFN_COND_XOR:inttype @0
+      (view_convert:inttype @1)
+      (bit_and (view_convert:inttype @2) { signs; })
+      (view_convert:inttype @3)))))))
+
 /* (x >= 0 ? x : 0) + (x <= 0 ? -x : 0) -> abs x.  */
 (simplify
   (plus:c (max @0 integer_zerop) (max (negate @0) integer_zerop))
diff --git a/gcc/testsuite/gcc.target/aarch64/sve/cond_xorsign_1.c b/gcc/testsuite/gcc.target/aarch64/sve/cond_xorsign_1.c
new file mode 100644
index 0000000..338ca60
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sve/cond_xorsign_1.c
@@ -0,0 +1,34 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+#define xorsign(A, B, SUFFIX) ((A) * __builtin_copysign##SUFFIX (1.0, B))
+
+#define DEF_LOOP(TYPE, SUFFIX)					\
+  void __attribute__ ((noinline, noclone))			\
+  test_##TYPE (TYPE *__restrict r, TYPE *__restrict a,		\
+	       TYPE *__restrict b, TYPE *__restrict c,		\
+	       int n)						\
+  {								\
+    for (int i = 0; i < n; ++i)					\
+      r[i] = a[i] < 20 ? xorsign(b[i], c[i], SUFFIX) : b[i];	\
+  }
+
+#define TEST_ALL(T) \
+  T (_Float16, f16) \
+  T (float, f) \
+  T (double, )
+
+TEST_ALL (DEF_LOOP)
+
+/* { dg-final { scan-assembler-times {\tand\tz[0-9]+\.h, z[0-9]+\.h,} 1 } } */
+/* { dg-final { scan-assembler-times {\tand\tz[0-9]+\.s, z[0-9]+\.s,} 1 } } */
+/* { dg-final { scan-assembler-times {\tand\tz[0-9]+\.d, z[0-9]+\.d,} 1 } } */
+
+/* { dg-final { scan-assembler-times {\teor\tz[0-9]+\.h, p[0-7]/m,} 1 } } */
+/* { dg-final { scan-assembler-times {\teor\tz[0-9]+\.s, p[0-7]/m,} 1 } } */
+/* { dg-final { scan-assembler-times {\teor\tz[0-9]+\.d, p[0-7]/m,} 1 } } */
+
+/* { dg-final { scan-assembler-not {\tfmul} } } */
+/* { dg-final { scan-assembler-not {\tmov\tz[^,]*z} } } */
+/* { dg-final { scan-assembler-not {\tmovprfx\t} } } */
+/* { dg-final { scan-assembler-not {\tsel\t} } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/sve/cond_xorsign_2.c b/gcc/testsuite/gcc.target/aarch64/sve/cond_xorsign_2.c
new file mode 100644
index 0000000..274dd0e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sve/cond_xorsign_2.c
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -msve-vector-bits=128 --param aarch64-autovec-preference=2" } */
+
+#include "cond_xorsign_1.c"
+
+/* { dg-final { scan-assembler-times {\tand\tz[0-9]+\.h, z[0-9]+\.h,} 1 } } */
+/* { dg-final { scan-assembler-times {\tand\tz[0-9]+\.s, z[0-9]+\.s,} 1 } } */
+/* { dg-final { scan-assembler-times {\tand\tz[0-9]+\.d, z[0-9]+\.d,} 1 } } */
+
+/* { dg-final { scan-assembler-times {\teor\tz[0-9]+\.h, p[0-7]/m,} 1 } } */
+/* { dg-final { scan-assembler-times {\teor\tz[0-9]+\.s, p[0-7]/m,} 1 } } */
+/* { dg-final { scan-assembler-times {\teor\tz[0-9]+\.d, p[0-7]/m,} 1 } } */
+
+/* { dg-final { scan-assembler-not {\tfmul} } } */
+/* { dg-final { scan-assembler-not {\tmov\tz[^,]*z} } } */
+/* { dg-final { scan-assembler-not {\tmovprfx\t} } } */
+/* { dg-final { scan-assembler-not {\tsel\t} } } */
diff --git a/gcc/tree.cc b/gcc/tree.cc
index 952bbec..80c0967 100644
--- a/gcc/tree.cc
+++ b/gcc/tree.cc
@@ -2695,6 +2695,35 @@ build_zero_cst (tree type)
     }
 }
 
+/* If floating-point type TYPE has an IEEE-style sign bit, return an
+   unsigned constant in which only the sign bit is set.  Return null
+   otherwise.  */
+
+tree
+sign_mask_for (tree type)
+{
+  /* Avoid having to choose between a real-only sign and a pair of signs.
+     This could be relaxed if the choice becomes obvious later.  */
+  if (TREE_CODE (type) == COMPLEX_TYPE)
+    return NULL_TREE;
+
+  auto eltmode = as_a<scalar_float_mode> (element_mode (type));
+  auto bits = REAL_MODE_FORMAT (eltmode)->ieee_bits;
+  if (!bits || !pow2p_hwi (bits))
+    return NULL_TREE;
+
+  tree inttype = unsigned_type_for (type);
+  if (!inttype)
+    return NULL_TREE;
+
+  auto mask = wi::set_bit_in_zero (bits - 1, bits);
+  if (TREE_CODE (inttype) == VECTOR_TYPE)
+    {
+      tree elt = wide_int_to_tree (TREE_TYPE (inttype), mask);
+      return build_vector_from_val (inttype, elt);
+    }
+  return wide_int_to_tree (inttype, mask);
+}
 
 /* Build a BINFO with LEN language slots.  */
 
@@ -10987,6 +11016,10 @@ signed_or_unsigned_type_for (int unsignedp, tree type)
 	return NULL_TREE;
       if (inner == inner2)
 	return type;
+      machine_mode new_mode;
+      if (VECTOR_MODE_P (TYPE_MODE (type))
+	  && related_int_vector_mode (TYPE_MODE (type)).exists (&new_mode))
+	return build_vector_type_for_mode (inner2, new_mode);
       return build_vector_type (inner2, TYPE_VECTOR_SUBPARTS (type));
     }
 
diff --git a/gcc/tree.h b/gcc/tree.h
index e730a2a..c656cd5 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -4675,6 +4675,7 @@ extern tree build_one_cst (tree);
 extern tree build_minus_one_cst (tree);
 extern tree build_all_ones_cst (tree);
 extern tree build_zero_cst (tree);
+extern tree sign_mask_for (tree);
 extern tree build_string (unsigned, const char * = NULL);
 extern tree build_poly_int_cst (tree, const poly_wide_int_ref &);
 extern tree build_tree_list (tree, tree CXX_MEM_STAT_INFO);