From 49e8c14ef6f1f968602a04c8499a672182590e87 Mon Sep 17 00:00:00 2001
From: Eugene Rozenfeld <erozen@microsoft.com>
Date: Wed, 9 Dec 2020 16:44:25 -0800
Subject: [PATCH] Optimize combination of comparisons to dec+compare

This patch adds patterns for optimizing
x < y || y == XXX_MIN to x <= y-1
x >= y && y != XXX_MIN to x > y-1
if y is an integer with TYPE_OVERFLOW_WRAPS.

This fixes pr96674.

Tested on x86_64-pc-linux-gnu.

For this function

bool f(unsigned a, unsigned b)
{
    return (b == 0) | (a < b);
}

the code without the patch is

test   esi,esi
sete   al
cmp    esi,edi
seta   dl
or     eax,edx
ret

the code with the patch is

sub    esi,0x1
cmp    esi,edi
setae  al
ret

	PR tree-optimization/96674
gcc/
	* match.pd: New patterns: x < y || y == XXX_MIN --> x <= y - 1
	x >= y && y != XXX_MIN --> x > y - 1

gcc/testsuite
	* gcc.dg/pr96674.c: New tests.
---
 gcc/match.pd                   | 14 ++++++++++++
 gcc/testsuite/gcc.dg/pr96674.c | 40 ++++++++++++++++++++++++++++++++++
 2 files changed, 54 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/pr96674.c

diff --git a/gcc/match.pd b/gcc/match.pd
index 7158e983d21..05e7ba9a333 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -2159,6 +2159,20 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
     (if (eqne == NE_EXPR)
      { constant_boolean_node (true, type); }))))
 
+/* y == XXX_MIN || x < y --> x <= y - 1 */
+(simplify
+ (bit_ior:c (eq:s @1 min_value) (lt:s @0 @1))
+  (if (INTEGRAL_TYPE_P (TREE_TYPE (@1))
+       && TYPE_OVERFLOW_WRAPS (TREE_TYPE (@1)))
+  (le @0 (minus @1 { build_int_cst (TREE_TYPE (@1), 1); }))))
+
+/* y != XXX_MIN && x >= y --> x > y - 1 */
+(simplify
+ (bit_and:c (ne:s @1 min_value) (ge:s @0 @1))
+  (if (INTEGRAL_TYPE_P (TREE_TYPE (@1))
+       && TYPE_OVERFLOW_WRAPS (TREE_TYPE (@1)))
+  (gt @0 (minus @1 { build_int_cst (TREE_TYPE (@1), 1); }))))
+
 /* Convert (X == CST1) && (X OP2 CST2) to a known value
    based on CST1 OP2 CST2.  Similarly for (X != CST1).  */
 
diff --git a/gcc/testsuite/gcc.dg/pr96674.c b/gcc/testsuite/gcc.dg/pr96674.c
new file mode 100644
index 00000000000..194ce2e6352
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr96674.c
@@ -0,0 +1,40 @@
+/* { dg-do run } */
+/* { dg-options "-O -fdump-tree-optimized -fwrapv" } */
+
+#include <limits.h>
+#include <stdbool.h>
+
+bool __attribute__ ((noipa)) test1 (unsigned a, unsigned b)
+{
+    return (b == 0) | (a < b);
+}
+
+bool __attribute__ ((noipa)) test2 (int a, int b)
+{
+    return (b == INT_MIN) | (a < b);
+}
+
+bool __attribute__ ((noipa)) test3 (unsigned a, unsigned b)
+{
+    return (b != 0) & (a >= b);
+}
+
+bool __attribute__ ((noipa)) test4 (int a, int b)
+{
+    return (b != INT_MIN) & (a >= b);
+}
+
+int main()
+{
+    if (!test1 (1, 0) || !test1 (1, 2) || test1 (2, 1) ||
+        !test2 (1, INT_MIN) || !test2 (1, 2) || test2 (2, 1) ||
+        test3 (1, 0) || test3 (1, 2) || !test3 (2, 1) ||
+        test4 (1, INT_MIN) || test4 (1, 2) || !test4 (2, 1)) {
+        __builtin_abort();	
+    }    	
+
+    return 0;
+}
+
+/* { dg-final { scan-tree-dump-times "\\+ 4294967295;" 2 "optimized" } } */
+/* { dg-final { scan-tree-dump-times "\\+ -1;" 2 "optimized" } } */
-- 
2.30.2