Clear EAF_NOCLOBBER for indirect calls

gcc/ChangeLog:

2021-08-22  Jan Hubicka  <hubicka@ucw.cz>
	    Martin Liska  <mliska@suse.cz>

	PR middle-end/101949
	* ipa-modref.c (analyze_ssa_name_flags): Indirect call implies
	~EAF_NOCLOBBER.

gcc/testsuite/ChangeLog:

2021-08-22  Jan Hubicka  <hubicka@ucw.cz>
	    Martin Liska  <mliska@suse.cz>

	* gcc.dg/lto/pr101949_0.c: New test.
	* gcc.dg/lto/pr101949_1.c: New test.

gcc/ipa-modref.c

@@ -1700,6 +1700,15 @@ analyze_ssa_name_flags (tree name, vec<modref_lattice> &lattice, int depth,
       else if (gcall *call = dyn_cast <gcall *> (use_stmt))
 	{
 	  tree callee = gimple_call_fndecl (call);
+
+	  /* IPA PTA internally it treats calling a function as "writing" to
+	     the argument space of all functions the function pointer points to
+	     (PR101949).  We can not drop EAF_NOCLOBBER only when ipa-pta
+	     is on since that would allow propagation of this from -fno-ipa-pta
+	     to -fipa-pta functions.  */
+	  if (gimple_call_fn (use_stmt) == name)
+	    lattice[index].merge (~EAF_NOCLOBBER);
+
 	  /* Return slot optimization would require bit of propagation;
 	     give up for now.  */
 	  if (gimple_call_return_slot_opt_p (call)

gcc/testsuite/gcc.dg/lto/pr101949_0.c

@@ -0,0 +1,20 @@
+/* { dg-lto-do run } */
+/* { dg-lto-options { "-O2 -fipa-pta -flto -flto-partition=1to1" } } */
+
+extern int bar (int (*)(int *), int *);
+
+static int x;
+
+static int __attribute__ ((noinline)) foo (int *p)
+{
+  *p = 1;
+  x = 0;
+  return *p;
+}
+
+int main ()
+{
+  if (bar (foo, &x) != 0)
+    __builtin_abort ();
+  return 0;
+}

gcc/testsuite/gcc.dg/lto/pr101949_1.c

@@ -0,0 +1,4 @@
+int __attribute__((noinline,noclone)) bar (int (*fn)(int *), int *p)
+{
+  return fn (p);
+}