On Thu, May 07, 2020 at 09:59:57AM +0200, Richard Biener wrote:
> Maybe write A - B + -1 >= A to actually match what you match below
...
> on the plus :c is not needed, canonicalization will put the constant
> literal second
>
> The previous pattern has a single_use check on the minus, since
> the result is always "simple" (a single stmt) the :s have no
> effect (hmm, I guess a genmatch warning for this case might be nice).
>
> And yes, if the TYPE_OVERFLOW_WRAPS checks are unnecessary remove
> them please, we'll hopefully resist all attempts to ubsan
> unsigned overflow ...
So like this if it passes bootstrap/regtest?
2020-05-07 Jakub Jelinek <ja...@redhat.com>
PR tree-optimization/94913
* match.pd (A - B + -1 >= A to B >= A): New simplification.
(A - B > A to A < B): Don't test TYPE_OVERFLOW_WRAPS which is always
true for TYPE_UNSIGNED integral types.
* gcc.dg/tree-ssa/pr94913.c: New test.
--- gcc/match.pd.jj 2020-05-06 11:18:35.000000000 +0200
+++ gcc/match.pd 2020-05-07 15:52:41.450787729 +0200
@@ -4787,10 +4787,17 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(cmp:c (minus@2 @0 @1) @0)
(if (single_use (@2)
&& ANY_INTEGRAL_TYPE_P (TREE_TYPE (@0))
- && TYPE_UNSIGNED (TREE_TYPE (@0))
- && TYPE_OVERFLOW_WRAPS (TREE_TYPE (@0)))
+ && TYPE_UNSIGNED (TREE_TYPE (@0)))
(cmp @1 @0))))
+/* Optimize A - B + -1 >= A into B >= A for unsigned comparisons. */
+(for cmp (ge lt)
+ (simplify
+ (cmp:c (plus (minus @0 @1) integer_minus_onep) @0)
+ (if (ANY_INTEGRAL_TYPE_P (TREE_TYPE (@0))
+ && TYPE_UNSIGNED (TREE_TYPE (@0)))
+ (cmp @1 @0))))
+
/* Testing for overflow is unnecessary if we already know the result. */
/* A - B > A */
(for cmp (gt le)
--- gcc/testsuite/gcc.dg/tree-ssa/pr94913.c.jj 2020-05-06 15:20:08.306376994
+0200
+++ gcc/testsuite/gcc.dg/tree-ssa/pr94913.c 2020-05-06 15:19:45.120725533
+0200
@@ -0,0 +1,33 @@
+/* PR tree-optimization/94913 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+/* { dg-final { scan-tree-dump " (?:b_\[0-9]+\\\(D\\\) >= a|a_\[0-9]+\\\(D\\\)
<= b)_\[0-9]+\\\(D\\\);" "optimized" } } */
+/* { dg-final { scan-tree-dump " (?:c_\[0-9]+\\\(D\\\) > d|d_\[0-9]+\\\(D\\\)
< c)_\[0-9]+\\\(D\\\);" "optimized" } } */
+/* { dg-final { scan-tree-dump " (?:f_\[0-9]+\\\(D\\\) >= e|e_\[0-9]+\\\(D\\\)
<= f)_\[0-9]+\\\(D\\\);" "optimized" } } */
+/* { dg-final { scan-tree-dump " (?:g_\[0-9]+\\\(D\\\) > h|h_\[0-9]+\\\(D\\\)
< g)_\[0-9]+\\\(D\\\);" "optimized" } } */
+
+int
+foo (unsigned a, unsigned b)
+{
+ return (a - b - 1) >= a;
+}
+
+int
+bar (unsigned c, unsigned d)
+{
+ return (c - d - 1) < c;
+}
+
+int
+baz (unsigned e, unsigned f)
+{
+ unsigned t = e - f;
+ return (t - 1) >= e;
+}
+
+int
+qux (unsigned g, unsigned h)
+{
+ unsigned t = g - h;
+ return (t - 1) < g;
+}
Jakub
