From: Reshma Roy <Reshma.Roy@amd.com>
Date: Thu, 30 Jul 2026 06:49:08 +0000 (+0530)
Subject: match: Fix incorrect identification of POPCOUNT pattern [PR126466]
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=7decbb57670c3c0f6136be00456fe9c8a41f7aed;p=thirdparty%2Fgcc.git

match: Fix incorrect identification of POPCOUNT pattern [PR126466]

This fixes r17-489-g8ca1e887847e2f, which added a third 32-bit
Hacker's Delight popcount matcher.  Its predicate checked
compare_tree_int (@5, 0x0F0F0F0F) twice and never validated the
final outer AND constant (@7), so any mask was accepted once the
earlier constants matched.

Require compare_tree_int (@7, 0x0000003F) so only the intended
popcount idiom is folded to IFN_POPCOUNT.

gcc/ChangeLog:

	PR tree-optimization/126466
	* match.pd: Fix incorrect POPCOUNT identification in the third
	32-bit Hacker's Delight matcher.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/popcount10.c: New test.
---

diff --git a/gcc/match.pd b/gcc/match.pd
index cfaead7c67d..00a0adaba87 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -11258,7 +11258,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 	&& compare_tree_int (@1, 0x55555555) == 0
 	&& compare_tree_int (@3, 0x33333333) == 0
 	&& compare_tree_int (@5, 0x0F0F0F0F) == 0
-	&& compare_tree_int (@5, 0x0F0F0F0F) == 0)
+	&& compare_tree_int (@7, 0x0000003F) == 0)
      (if (direct_internal_fn_supported_p (IFN_POPCOUNT, type,
 					  OPTIMIZE_FOR_BOTH))
 	(convert (IFN_POPCOUNT:type @0))))))
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/popcount10.c b/gcc/testsuite/gcc.dg/tree-ssa/popcount10.c
new file mode 100644
index 00000000000..ed894618690
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/popcount10.c
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target popcount } */
+/* { dg-require-effective-target int32plus } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+const unsigned m1  = 0x55555555UL;
+const unsigned m2  = 0x33333333UL;
+const unsigned m3  = 0x0F0F0F0FUL;
+const unsigned m4  = 0x0000FFFFUL;
+
+int popc(unsigned x) {
+  x = x - ((x >> 1) & m1);
+  x = x - 3*((x >> 2) & m2);
+  x = (x + (x >> 4)) & m3;
+  x = x + (x >> 8);
+  x = x + (x >> 16);
+  return x & m4;
+}
+
+/* { dg-final { scan-tree-dump-not "\.POPCOUNT" "optimized" } } */