[PATCH] match.pd: Add new division pattern [PR104992]

[Sam Feifer <sfeifer@redhat.com>]

This patch fixes a missed optimization in match.pd. It takes the pattern, x / y * y == x, and optimizes it to x % y == 0. This produces fewer instructions.

There are also tests for the optimizations to be added to the test suite.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

	PR tree-optimization/104992

gcc/ChangeLog:

	* match.pd x / y * y == x: New simplification.

gcc/testsuite/ChangeLog:

	* gcc.dg/pr104992-1.c: New test.
	* gcc.dg/pr104992.c: New test.
---
 gcc/match.pd                      |  5 +++++
 gcc/testsuite/gcc.dg/pr104992-1.c | 30 ++++++++++++++++++++++++++
 gcc/testsuite/gcc.dg/pr104992.c   | 35 +++++++++++++++++++++++++++++++
 3 files changed, 70 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/pr104992-1.c
 create mode 100644 gcc/testsuite/gcc.dg/pr104992.c

diff --git a/gcc/match.pd b/gcc/match.pd
index 9736393061a..f7ab2174b8a 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -8054,3 +8054,8 @@ and,
       (if (TYPE_UNSIGNED (TREE_TYPE (@0)))
         (bit_and @0 @1)
       (cond (le @0 @1) @0 (bit_and @0 @1))))))
+
+/* x / y * y == x -> x % y == 0.  */
+(simplify
+  (eq (mult (trunc_div @0 @1) @1) @0)
+  (eq (trunc_mod @0 @1) { build_zero_cst TREE_TYPE(@0); }))
diff --git a/gcc/testsuite/gcc.dg/pr104992-1.c b/gcc/testsuite/gcc.dg/pr104992-1.c
new file mode 100644
index 00000000000..a80e5e180ce
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr104992-1.c
@@ -0,0 +1,30 @@
+/* PR tree-optimization/104992 */
+/* { dg-do run } */
+/* { dg-options "-O2"} */
+
+#include "pr104992.c"
+
+int main () {
+
+    /* Should be true.  */
+    if (!foo(6, 3)
+        || !bar(12, 2)
+        || !baz(34, 17)
+        || !qux(50, 10)
+        || !fred(16, 8)
+        || !baz(-9, 3)
+        || !baz(9, -3)
+        || !baz(-9, -3)
+        ) {
+            __builtin_abort();
+         }
+    
+    /* Should be false.  */
+    if (foo(5, 30)
+        || bar(72, 27)
+        || baz(42, 15)) {
+            __builtin_abort();
+        }
+    
+    return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/pr104992.c b/gcc/testsuite/gcc.dg/pr104992.c
new file mode 100644
index 00000000000..b4b0ca53118
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr104992.c
@@ -0,0 +1,35 @@
+/* PR tree-optimization/104992 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+/* Form from PR.  */
+__attribute__((noipa)) unsigned foo(unsigned x, unsigned y)
+{
+    return x / y * y == x;
+}
+
+__attribute__((noipa)) unsigned bar(unsigned x, unsigned y) {
+    return x == x / y * y;
+}
+
+/* Signed test case.  */
+__attribute__((noipa)) unsigned baz (int x, int y) {
+    return x / y * y == x;
+}
+
+/* Changed order.  */
+__attribute__((noipa)) unsigned qux (unsigned x, unsigned y) {
+    return y * (x / y) == x;
+}
+
+/* Wrong order.  */
+__attribute__((noipa)) unsigned fred (unsigned x, unsigned y) {
+    return y * x / y == x;
+}
+
+/* Wrong pattern.  */
+__attribute__((noipa)) unsigned waldo (unsigned x, unsigned y, unsigned z) {
+    return x / y * z == x;
+}
+
+/* { dg-final {scan-tree-dump-times " % " 4 "optimized" } } */

base-commit: 633e9920589ddfaf2d6da1c24ce99b18a2638db4
-- 
2.31.1