--- gcc/c/c-parser.cc.jj	2025-01-06 10:07:33.585493775 +0100
+++ gcc/c/c-parser.cc	2025-01-09 16:12:07.761005082 +0100
@@ -12906,6 +12906,7 @@ c_parser_postfix_expression (c_parser *p
 		  expr.value = build2_loc (loc, COMPOUND_EXPR,
 					   TREE_TYPE (expr.value),
 					   instrument_expr, expr.value);
+		set_c_expr_source_range (&expr, loc, close_paren_loc);
 		break;
 	      }
 	    tree barg1 = arg;
--- gcc/testsuite/gcc.dg/pr118376.c.jj	2025-01-09 16:26:19.621072359 +0100
+++ gcc/testsuite/gcc.dg/pr118376.c	2025-01-09 16:26:04.608283459 +0100
@@ -0,0 +1,11 @@
+/* PR c/118376 */
+/* { dg-do compile } */
+/* { dg-options "-Wsign-conversion" } */
+
+unsigned x;
+
+void
+foo ()
+{
+  __builtin_memset (&x, (long long) __builtin_stdc_rotate_right (x, 0), 1);
+} /* { dg-warning "conversion to 'int' from 'long long int' may change the sign of the result" "" { target *-*-* } .-1 } */