[PATCH] Fix PR87024

[Richard Biener]

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk 
sofar.

Richard.

2018-08-23  Richard Biener  <rguent...@suse.de>

        PR middle-end/87024
        * tree-inline.c (copy_bb): Drop unused __builtin_va_arg_pack_len
        calls.

        * gcc.dg/pr87024.c: New testcase.

diff --git a/gcc/testsuite/gcc.dg/pr87024.c b/gcc/testsuite/gcc.dg/pr87024.c
new file mode 100644
index 00000000000..a8a58aafc26
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr87024.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fno-tree-dce" } */
+
+static inline void __attribute__((always_inline))
+mp ()
+{
+  (void) __builtin_va_arg_pack_len ();
+}
+
+void
+ui (void)
+{
+  mp ();
+}
diff --git a/gcc/tree-inline.c b/gcc/tree-inline.c
index 2b6bb5c0e31..ef615cc347e 100644
--- a/gcc/tree-inline.c
+++ b/gcc/tree-inline.c
@@ -1951,7 +1951,13 @@ copy_bb (copy_body_data *id, basic_block bb,
              for (p = DECL_ARGUMENTS (id->src_fn); p; p = DECL_CHAIN (p))
                nargs--;
 
-             if (!gimple_call_va_arg_pack_p (id->call_stmt))
+             if (!gimple_call_lhs (stmt))
+               {
+                 /* Drop unused calls.  */
+                 gsi_remove (&copy_gsi, false);
+                 continue;
+               }
+             else if (!gimple_call_va_arg_pack_p (id->call_stmt))
                {
                  count = build_int_cst (integer_type_node, nargs);
                  new_stmt = gimple_build_assign (gimple_call_lhs (stmt), 
count);