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From: "hubicka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/103266] [12 regression] llvm-13
 miscompilation: __builtin_assume_aligned causes over-aggressive dce
Date: Thu, 18 Nov 2021 17:08:48 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103266

--- Comment #7 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
I am testing
diff --git a/gcc/ipa-modref.c b/gcc/ipa-modref.c
index c94f0589d44..e5d2b11025a 100644
--- a/gcc/ipa-modref.c
+++ b/gcc/ipa-modref.c
@@ -2033,10 +2033,7 @@ modref_eaf_analysis::merge_call_lhs_flags (gcall *ca=
ll,
int arg,
                                           bool indirect)
 {
   int index =3D SSA_NAME_VERSION (name);
-
-  /* If value is not returned at all, do nothing.  */
-  if (!direct && !indirect)
-    return;
+  bool returned_directly =3D false;

   /* If there is no return value, no flags are affected.  */
   if (!gimple_call_lhs (call))
@@ -2047,10 +2044,23 @@ modref_eaf_analysis::merge_call_lhs_flags (gcall *c=
all,
int arg,
   if (arg >=3D 0)
     {
       int flags =3D gimple_call_return_flags (call);
-      if ((flags & ERF_RETURNS_ARG)
-         && (flags & ERF_RETURN_ARG_MASK) !=3D arg)
-       return;
+      if (flags & ERF_RETURNS_ARG)
+       {
+         if ((flags & ERF_RETURN_ARG_MASK) =3D=3D arg)
+           returned_directly =3D true;
+         else
+          return;
+       }
+    }
+  /* Make ERF_RETURNS_ARG overwrite EAF_UNUSED.  */
+  if (returned_directly)
+    {
+      direct =3D true;
+      indirect =3D false;
     }
+  /* If value is not returned at all, do nothing.  */
+  else if (!direct && !indirect)
+    return;

   /* If return value is SSA name determine its flags.  */
   if (TREE_CODE (gimple_call_lhs (call)) =3D=3D SSA_NAME)
@@ -2273,11 +2283,13 @@ modref_eaf_analysis::analyze_ssa_name (tree name)
                if (gimple_call_arg (call, i) =3D=3D name)
                  {
                    int call_flags =3D gimple_call_arg_flags (call, i);
-                   if (!ignore_retval && !(call_flags & EAF_UNUSED))
+                   if (!ignore_retval)
                      merge_call_lhs_flags
                              (call, i, name,
-                              !(call_flags & EAF_NOT_RETURNED_DIRECTLY),
-                              !(call_flags & EAF_NOT_RETURNED_INDIRECTLY));
+                              !(call_flags & (EAF_NOT_RETURNED_DIRECTLY
+                                              | EAF_UNUSED)),
+                              !(call_flags & (EAF_NOT_RETURNED_INDIRECTLY
+                                              | EAF_UNUSED)));
                    if (!(ecf_flags & (ECF_CONST | ECF_NOVOPS)))
                      {
                        call_flags =3D callee_to_caller_flags=