From fdabed7b0b37c02c8fb711e0d30938fae2a1ccd8 Mon Sep 17 00:00:00 2001
From: Sam Feifer <sfeifer@redhat.com>
Date: Fri, 29 Jul 2022 09:44:48 -0400
Subject: [PATCH] match.pd: Add new division pattern [PR104992]

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. This simplification does not happen for complex types.

This patch also adds tests for the optimization rule.

Bootstrapped/regtested on x86_64-pc-linux-gnu.

	PR tree-optimization/104992

gcc/ChangeLog:

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

gcc/testsuite/ChangeLog:

	* g++.dg/pr104992-1.C: New test.
	* gcc.dg/pr104992.c: New test.
---
 gcc/match.pd                      |  6 ++++
 gcc/testsuite/g++.dg/pr104992-1.C | 30 ++++++++++++++++
 gcc/testsuite/gcc.dg/pr104992.c   | 57 +++++++++++++++++++++++++++++++
 3 files changed, 93 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/pr104992-1.C
 create mode 100644 gcc/testsuite/gcc.dg/pr104992.c

diff --git a/gcc/match.pd b/gcc/match.pd
index 330c1db0c8e..562138a8034 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -3982,6 +3982,12 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
    (plus:c (mult:c (div @0 @1) @1) (mod @0 @1))
    @0))
 
+/* x / y * y == x -> x % y == 0.  */
+(simplify
+  (eq:c (mult:c (trunc_div:s @0 @1) @1) @0)
+  (if (TREE_CODE (TREE_TYPE (@0)) != COMPLEX_TYPE)
+    (eq (trunc_mod @0 @1) { build_zero_cst (TREE_TYPE (@0)); })))
+
 /* ((X /[ex] A) +- B) * A  -->  X +- A * B.  */
 (for op (plus minus)
  (simplify
diff --git a/gcc/testsuite/g++.dg/pr104992-1.C b/gcc/testsuite/g++.dg/pr104992-1.C
new file mode 100644
index 00000000000..f5696b245ac
--- /dev/null
+++ b/gcc/testsuite/g++.dg/pr104992-1.C
@@ -0,0 +1,30 @@
+/* PR tree-optimization/104992 */
+/* { dg-do run } */
+/* { dg-options "-O2"} */
+
+#include "../gcc.dg/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..b9d91a13ad8
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr104992.c
@@ -0,0 +1,57 @@
+/* PR tree-optimization/104992 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+#define vector __attribute__((vector_size(4*sizeof(int))))
+
+/* 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;
+}
+
+/* Test for forward propogation.  */
+__attribute__((noipa)) unsigned corge(unsigned x, unsigned y) {
+    int z = x / y;
+    int q = z * y;
+    return q == x; 
+}
+
+/* Test vector case.  */
+__attribute__((noipa)) vector int thud(vector int x, vector int y) {
+    return x / y * y == x;
+}
+
+/* Complex type should not simplify because mod is different.  */
+__attribute__((noipa)) int goo(_Complex int x, _Complex int y)
+{
+    _Complex int z = x / y;
+    _Complex int q = z * y;
+    return q == 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 " % " 9 "optimized" } } */

base-commit: 6e0ca3fe88d8f98ba6b4009c9483e87afbcf4ee8
-- 
2.31.1