[RFA] [PR tree-optimization/90949] Don't propagate context sensitive non-nullness when copy-propagating pointers

[Jeff Law]

As outlined in the BZ, our alias analysis code is context insensitive.
So when we copy-propagate pointers, we can can and do copy PTA
information from members to the representative pointer in the copy-of
chain (we do this when the representative pointer has no associated PTA
information).

However, [E]VRP can set the non-nullness of a pointer using context
sensitive information.  So we have to be more careful when copying PTA
information.

We already have similar issues with alignment information as well.  This
patch just extends the hack to avoid copying alignment information in
some circumstances to also avoid copying the non-nullness property.

Bootstrapped and regression tested on x86_64-linux-gnu.  OK for the trunk?

Jeff
-------------- next part --------------
	* tree-ssa-copy.c (fini_copy_prop): Call clear_ptr_nonnull as needed.
	* tree-ssanames.c (clear_ptr_nonnull): New function.
	* tree-ssanames.h (clear_ptr_nonnull): Declare.

	* gcc.c-torture/execute/pr90949.c: New test.

diff --git a/gcc/testsuite/gcc.c-torture/execute/pr90949.c b/gcc/testsuite/gcc.c-torture/execute/pr90949.c
new file mode 100644
index 00000000000..12ae31d97a5
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/pr90949.c
@@ -0,0 +1,33 @@
+void __attribute__((noipa,noinline)) my_puts (const char *str) { }
+void __attribute__((noipa,noinline)) my_free (void *p) { }
+
+
+struct Node
+{
+    struct Node* child;
+};
+
+char *space[sizeof (struct Node) * 2] = { };
+
+void * __attribute__((noipa,noinline)) my_malloc (int bytes) { return &space;} 
+
+void walk(struct Node* module, int cleanup)
+{
+    if (module == 0) {
+        return;
+    }
+    if (!cleanup) {
+        my_puts("No cleanup");
+    }
+    walk(module->child, cleanup);
+    if (cleanup) {
+        my_free(module);
+    }
+}
+
+int main()
+{
+    struct Node* node = my_malloc(sizeof(struct Node));
+    node->child = 0;
+    walk(node, 1);
+}
diff --git a/gcc/tree-ssa-copy.c b/gcc/tree-ssa-copy.c
index 89532633e42..ccb95bf18b7 100644
--- a/gcc/tree-ssa-copy.c
+++ b/gcc/tree-ssa-copy.c
@@ -548,10 +548,28 @@ fini_copy_prop (void)
 		 but alignment info might be cfg sensitive, if it
 		 e.g. is derived from VRP derived non-zero bits.
 		 So, do not copy alignment info if the two SSA_NAMEs
-		 aren't defined in the same basic block.  */
+		 aren't defined in the same basic block.
+
+		 Similarly, we may have a context sensitive non-NULL
+		 state for an SSA_NAME (call it A), which in turn is
+		 used to derive a global non-NULL state for a different
+		 SSA_NAME (call it B) via a PHI node.
+
+		 That PHI node also represents a copy which we will try
+		 to eliminate here.  We will copy the alias info to the
+		 representative element in the copy-of chains.  If A is
+		 the representative element, then we just made A globally
+		 non-NULL which is incorrect.
+
+		 Arguably one might claim this is too fragile and that we
+		 should never dupicate the points-to information if the
+		 objects are in different blocks.  */
 	      if (var_bb != copy_of_bb)
-		mark_ptr_info_alignment_unknown
-				(SSA_NAME_PTR_INFO (copy_of[i].value));
+		{
+		  mark_ptr_info_alignment_unknown
+				  (SSA_NAME_PTR_INFO (copy_of[i].value));
+		  clear_ptr_nonnull (copy_of[i].value);
+		}
 	    }
 	  else if (!POINTER_TYPE_P (TREE_TYPE (var))
 		   && SSA_NAME_RANGE_INFO (var)
diff --git a/gcc/tree-ssanames.c b/gcc/tree-ssanames.c
index 5bac799e9a3..2114a9584ba 100644
--- a/gcc/tree-ssanames.c
+++ b/gcc/tree-ssanames.c
@@ -451,6 +451,16 @@ get_range_info (const_tree name, value_range_base &vr)
   return kind;
 }
 
+/* Clear nonnull attribute to pointer NAME.  */
+
+void
+clear_ptr_nonnull (tree name)
+{
+  gcc_assert (POINTER_TYPE_P (TREE_TYPE (name)));
+  struct ptr_info_def *pi = get_ptr_info (name);
+  pi->pt.null = 1;
+}
+
 /* Set nonnull attribute to pointer NAME.  */
 
 void
diff --git a/gcc/tree-ssanames.h b/gcc/tree-ssanames.h
index 6e6cffbce6a..6470d491deb 100644
--- a/gcc/tree-ssanames.h
+++ b/gcc/tree-ssanames.h
@@ -91,6 +91,7 @@ extern void set_ptr_info_alignment (struct ptr_info_def *, unsigned int,
 extern void adjust_ptr_info_misalignment (struct ptr_info_def *, poly_uint64);
 extern struct ptr_info_def *get_ptr_info (tree);
 extern void set_ptr_nonnull (tree);
+extern void clear_ptr_nonnull (tree);
 extern bool get_ptr_nonnull (const_tree);
 
 extern tree copy_ssa_name_fn (struct function *, tree, gimple *);