VEC_COND_EXPR optimizations

When vector comparisons were forced to use vec_cond_expr, we lost a number of optimizations (my fault for not adding enough testcases to
prevent that). This patch tries to unwrap vec_cond_expr a bit so some optimizations can still happen.

I wasn't planning to add all those transformations together, but adding one caused a regression, whose fix introduced a second regression,
etc.

Restricting to constant folding would not be sufficient, we also need at least things like X|0 or X&X. The transformations are quite
conservative with :s and folding only if everything simplifies, we may want to relax this later. And of course we are going to miss things
like a?b:c + a?c:b -> b+c.

In terms of number of operations, some transformations turning 2 VEC_COND_EXPR into VEC_COND_EXPR + BIT_IOR_EXPR + BIT_NOT_EXPR might not look
like a gain... I expect the bit_not disappears in most cases, and VEC_COND_EXPR looks more costly than a simpler BIT_IOR_EXPR.

2020-08-05  Marc Glisse  <marc.glisse@inria.fr>

	PR tree-optimization/95906
	PR target/70314
	* match.pd ((c ? a : b) op d, (c ? a : b) op (c ? d : e),
	(v ? w : 0) ? a : b, c1 ? c2 ? a : b : b): New transformations.
	(op (c ? a : b)): Update to match the new transformations.

	* gcc.dg/tree-ssa/andnot-2.c: New file.
	* gcc.dg/tree-ssa/pr95906.c: Likewise.
	* gcc.target/i386/pr70314.c: Likewise.

gcc/match.pd

@@ -3436,20 +3436,66 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
   (if (integer_zerop (@0))
    @2)))
 
-/* Sink unary operations to constant branches, but only if we do fold it to
-   constants.  */
+#if GIMPLE
+/* Sink unary operations to branches, but only if we do fold both.  */
 (for op (negate bit_not abs absu)
  (simplify
-  (op (vec_cond @0 VECTOR_CST@1 VECTOR_CST@2))
-  (with
-   {
-     tree cst1, cst2;
-     cst1 = const_unop (op, type, @1);
-     if (cst1)
-       cst2 = const_unop (op, type, @2);
-   }
-   (if (cst1 && cst2)
-    (vec_cond @0 { cst1; } { cst2; })))))
+  (op (vec_cond:s @0 @1 @2))
+  (vec_cond @0 (op! @1) (op! @2))))
+
+/* Sink binary operation to branches, but only if we can fold it.  */
+(for op (tcc_comparison plus minus mult bit_and bit_ior bit_xor
+	 rdiv trunc_div ceil_div floor_div round_div
+	 trunc_mod ceil_mod floor_mod round_mod min max)
+/* (c ? a : b) op (c ? d : e)  -->  c ? (a op d) : (b op e) */
+ (simplify
+  (op (vec_cond:s @0 @1 @2) (vec_cond:s @0 @3 @4))
+  (vec_cond @0 (op! @1 @3) (op! @2 @4)))
+
+/* (c ? a : b) op d  -->  c ? (a op d) : (b op d) */
+ (simplify
+  (op (vec_cond:s @0 @1 @2) @3)
+  (vec_cond @0 (op! @1 @3) (op! @2 @3)))
+ (simplify
+  (op @3 (vec_cond:s @0 @1 @2))
+  (vec_cond @0 (op! @3 @1) (op! @3 @2))))
+#endif
+
+/* (v ? w : 0) ? a : b is just (v & w) ? a : b  */
+(simplify
+ (vec_cond (vec_cond:s @0 @3 integer_zerop) @1 @2)
+ (if (types_match (@0, @3))
+  (vec_cond (bit_and @0 @3) @1 @2)))
+(simplify
+ (vec_cond (vec_cond:s @0 integer_all_onesp @3) @1 @2)
+ (if (types_match (@0, @3))
+  (vec_cond (bit_ior @0 @3) @1 @2)))
+(simplify
+ (vec_cond (vec_cond:s @0 integer_zerop @3) @1 @2)
+ (if (types_match (@0, @3))
+  (vec_cond (bit_ior @0 (bit_not @3)) @2 @1)))
+(simplify
+ (vec_cond (vec_cond:s @0 @3 integer_all_onesp) @1 @2)
+ (if (types_match (@0, @3))
+  (vec_cond (bit_and @0 (bit_not @3)) @2 @1)))
+
+/* c1 ? c2 ? a : b : b  -->  (c1 & c2) ? a : b  */
+(simplify
+ (vec_cond @0 (vec_cond:s @1 @2 @3) @3)
+ (if (types_match (@0, @1))
+  (vec_cond (bit_and @0 @1) @2 @3)))
+(simplify
+ (vec_cond @0 @2 (vec_cond:s @1 @2 @3))
+ (if (types_match (@0, @1))
+  (vec_cond (bit_ior @0 @1) @2 @3)))
+(simplify
+ (vec_cond @0 (vec_cond:s @1 @2 @3) @2)
+ (if (types_match (@0, @1))
+  (vec_cond (bit_ior (bit_not @0) @1) @2 @3)))
+(simplify
+ (vec_cond @0 @3 (vec_cond:s @1 @2 @3))
+ (if (types_match (@0, @1))
+  (vec_cond (bit_and (bit_not @0) @1) @2 @3)))
 
 /* Simplification moved from fold_cond_expr_with_comparison.  It may also
    be extended.  */

gcc/testsuite/gcc.dg/tree-ssa/andnot-2.c

@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-forwprop3-raw -w -Wno-psabi" } */
+
+typedef long vec __attribute__((vector_size(16)));
+vec f(vec x){
+  vec y = x < 10;
+  return y & (y == 0);
+}
+
+/* { dg-final { scan-tree-dump-not "_expr" "forwprop3" } } */

gcc/testsuite/gcc.dg/tree-ssa/pr95906.c

@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-forwprop3-raw -w -Wno-psabi" } */
+
+// FIXME: this should further optimize to a MAX_EXPR
+typedef signed char v16i8 __attribute__((vector_size(16)));
+v16i8 f(v16i8 a, v16i8 b)
+{
+    v16i8 cmp = (a > b);
+    return (cmp & a) | (~cmp & b);
+}
+
+/* { dg-final { scan-tree-dump-not "bit_(and|ior)_expr" "forwprop3" } } */
+/* { dg-final { scan-tree-dump-times "vec_cond_expr" 1 "forwprop3" } } */

gcc/testsuite/gcc.target/i386/pr70314.c

@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-march=skylake-avx512 -O2" } */
+/* { dg-final { scan-assembler-times "cmp" 2 } } */
+/* { dg-final { scan-assembler-not "and" } } */
+
+typedef long vec __attribute__((vector_size(16)));
+vec f(vec x, vec y){
+  return (x < 5) & (y < 8);
+}
+
+/* On x86_64, currently
+	vpcmpq	$2, .LC1(%rip), %xmm1, %k1
+	vpcmpq	$2, .LC0(%rip), %xmm0, %k0{%k1}
+	vpmovm2q	%k0, %xmm0
+*/