[PATCH] gimple: Ignore *0 = {CLOBBER} in path isolation [PR96722]

[Jakub Jelinek <jakub@redhat.com>]

Hi!

Clobbers of MEM_REF with NULL address are just fancy nops, something we just
ignore and don't emit any code for it (ditto for other clobbers), they just
mark end of life on something, so we shouldn't infer from those that there
is some UB.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2020-08-24  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/96722
	* gimple.c (infer_nonnull_range): Formatting fix.
	(infer_nonnull_range_by_dereference): Return false for clobber stmts.

	* g++.dg/opt/pr96722.C: New test.

--- gcc/gimple.c.jj	2020-08-03 22:54:51.417531677 +0200
+++ gcc/gimple.c	2020-08-24 13:23:22.082312349 +0200
@@ -2917,8 +2917,8 @@ check_loadstore (gimple *, tree op, tree
 bool
 infer_nonnull_range (gimple *stmt, tree op)
 {
-  return infer_nonnull_range_by_dereference (stmt, op)
-    || infer_nonnull_range_by_attribute (stmt, op);
+  return (infer_nonnull_range_by_dereference (stmt, op)
+	  || infer_nonnull_range_by_attribute (stmt, op));
 }
 
 /* Return true if OP can be inferred to be non-NULL after STMT
@@ -2930,7 +2930,8 @@ infer_nonnull_range_by_dereference (gimp
      non-NULL if -fdelete-null-pointer-checks is enabled.  */
   if (!flag_delete_null_pointer_checks
       || !POINTER_TYPE_P (TREE_TYPE (op))
-      || gimple_code (stmt) == GIMPLE_ASM)
+      || gimple_code (stmt) == GIMPLE_ASM
+      || gimple_clobber_p (stmt))
     return false;
 
   if (walk_stmt_load_store_ops (stmt, (void *)op,
--- gcc/testsuite/g++.dg/opt/pr96722.C.jj	2020-08-24 13:24:45.357132323 +0200
+++ gcc/testsuite/g++.dg/opt/pr96722.C	2020-08-24 13:25:06.224836626 +0200
@@ -0,0 +1,20 @@
+// PR tree-optimization/96722
+// { dg-do run }
+// { dg-options "-O2" }
+
+struct S { int s; ~S () {} };
+
+void
+foo (S *a)
+{
+  if (a)
+    return;
+  a->~S ();
+}
+
+int
+main ()
+{
+  S s;
+  foo (&s);
+}

	Jakub