[PATCH] match.pd: Fix up __builtin_mul_overflow_p signed type optimization [PR105984]

[Jakub Jelinek via Gcc-patches]

Hi!

Earlier in the simplification pattern, we require that @0 has compatible
type to the type of IMAGPART_EXPR, but for @1 which is a non-zero constant
all we require is that it the constant fits into that type.
Later the code checks if the constant is negative, because when min / max
values are divided by negative divisor, lo will be higher than hi.
In the following testcase, @1 has unsigned char type, while @0 has
int type, so @1 which is 254 is wi::neg_p and we were swapping lo and hi,
even when @1 cast to int isn't negative.

We could use tree_int_cst_sgn (@1) < 0 as the check instead and it would
work both for narrower types of @1 and even same or wider ones, but
I've noticed we probably don't want to call fold_convert (TREE_TYPE (@0), @1)
twice and when we save that result in a temporary, we can just use wi::neg_p
on that temporary.

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

2022-06-16  Jakub Jelinek  <ja...@redhat.com>

        PR tree-optimization/105984
        * match.pd (__builtin_mul_overflow_p (x, cst, (stype) 0) ->
        x > stype_max / cst || x < stype_min / cst): fold_convert @1
        to TREE_TYPE (@0) just once and test for negative divisor
        also on that folded constant instead of on @1.

        * gcc.c-torture/execute/pr105984.c: New test.

--- gcc/match.pd.jj     2022-06-15 10:43:46.000000000 +0200
+++ gcc/match.pd        2022-06-15 12:52:04.640981511 +0200
@@ -5995,16 +5995,15 @@ (define_operator_list SYNC_FETCH_AND_AND
       (convert (eq @0 { TYPE_MIN_VALUE (TREE_TYPE (@0)); }))
       (with
        {
+        tree div = fold_convert (TREE_TYPE (@0), @1);
         tree lo = int_const_binop (TRUNC_DIV_EXPR,
-                                   TYPE_MIN_VALUE (TREE_TYPE (@0)),
-                                   fold_convert (TREE_TYPE (@0), @1));
+                                   TYPE_MIN_VALUE (TREE_TYPE (@0)), div);
         tree hi = int_const_binop (TRUNC_DIV_EXPR,
-                                   TYPE_MAX_VALUE (TREE_TYPE (@0)),
-                                   fold_convert (TREE_TYPE (@0), @1));
+                                   TYPE_MAX_VALUE (TREE_TYPE (@0)), div);
         tree etype = range_check_type (TREE_TYPE (@0));
         if (etype)
           {
-            if (wi::neg_p (wi::to_wide (@1)))
+            if (wi::neg_p (wi::to_wide (div)))
               std::swap (lo, hi);
             lo = fold_convert (etype, lo);
             hi = fold_convert (etype, hi);
--- gcc/testsuite/gcc.c-torture/execute/pr105984.c.jj   2022-06-15 
13:11:30.695091900 +0200
+++ gcc/testsuite/gcc.c-torture/execute/pr105984.c      2022-06-15 
13:10:56.267443900 +0200
@@ -0,0 +1,19 @@
+/* PR tree-optimization/105984 */
+
+unsigned long long g;
+
+static inline unsigned long long
+foo (unsigned char c)
+{
+  g -= __builtin_mul_overflow_p (4, (unsigned char) ~c, 0);
+  return g;
+}
+
+int
+main ()
+{
+  unsigned long long x = foo (1);
+  if (x != 0)
+    __builtin_abort ();
+  return 0;
+}

        Jakub