From: David Malcolm <dmalcolm@redhat.com>
Date: Mon, 15 Dec 2025 16:48:49 +0000 (-0500)
Subject: analyzer: fold X + (-X) to zero [PR122975]
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c48970fc4a4d1747a50e6abd1634757212420c04;p=thirdparty%2Fgcc.git

analyzer: fold X + (-X) to zero [PR122975]

gcc/analyzer/ChangeLog:
	PR analyzer/122975
	* region-model-manager.cc (region_model_manager::maybe_fold_binop): Fold
	X + (-X) to zero.

gcc/testsuite/ChangeLog:
	PR analyzer/122975
	* c-c++-common/analyzer/arith-1.c: New test.
	* c-c++-common/analyzer/infinite-recursion-pr122975.c: New test.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>
---

diff --git a/gcc/analyzer/region-model-manager.cc b/gcc/analyzer/region-model-manager.cc
index 2a6d047f4ce..0b28b767a55 100644
--- a/gcc/analyzer/region-model-manager.cc
+++ b/gcc/analyzer/region-model-manager.cc
@@ -680,6 +680,11 @@ region_model_manager::maybe_fold_binop (tree type, enum tree_code op,
       /* (VAL + 0) -> VAL.  */
       if (cst1 && zerop (cst1))
 	return get_or_create_cast (type, arg0);
+      /* X + (-X) -> 0.  */
+      if (const unaryop_svalue *unary_op = arg1->dyn_cast_unaryop_svalue ())
+	if (unary_op->get_op () == NEGATE_EXPR
+	    && unary_op->get_arg () == arg0)
+	  return get_or_create_int_cst (type, 0);
       break;
     case MINUS_EXPR:
       /* (VAL - 0) -> VAL.  */
diff --git a/gcc/testsuite/c-c++-common/analyzer/arith-1.c b/gcc/testsuite/c-c++-common/analyzer/arith-1.c
new file mode 100644
index 00000000000..af58466c7bc
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/analyzer/arith-1.c
@@ -0,0 +1,13 @@
+#include "analyzer-decls.h"
+
+static int __attribute__((noipa))
+negate_int (int x)
+{
+  return -x;
+}
+
+void
+test_1 (int a)
+{
+  __analyzer_eval (a + negate_int (a) == 0); /* { dg-warning "TRUE" } */
+}
diff --git a/gcc/testsuite/c-c++-common/analyzer/infinite-recursion-pr122975.c b/gcc/testsuite/c-c++-common/analyzer/infinite-recursion-pr122975.c
new file mode 100644
index 00000000000..c241f4169f7
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/analyzer/infinite-recursion-pr122975.c
@@ -0,0 +1,5 @@
+void fun(int x, int y)
+{
+  if (x + y != 0) 
+    fun(x, -x); /* { dg-bogus "infinite recursion" } */
+}