[PATCH] Fix wrong-code aggregate propagate_with_phi bug (PR tree-optimization/81365)

[Jakub Jelinek <jakub@redhat.com>]

Hi!

As mentioned in the PR, for aggregate copies we fail to verify there
are no loads in between the PHI and the aggregate copy that could alias with the
lhs of the copy, which is needed, because we want to hoist the aggregate
copy onto predecessor edges of the bb with the PHI.

The following patch implements that, bootstrapped/regtested on x86_64-linux
and i686-linux, ok for trunk and after a while 7.x?

2017-07-13  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/81365
	* tree-ssa-phiprop.c (propagate_with_phi): When considering hoisting
	aggregate moves onto bb predecessor edges, make sure there are no
	loads that could alias the lhs in between the start of bb and the
	loads from *phi.  If there are any debug stmts that could alias,
	reset them.

	* g++.dg/torture/pr81365.C: New test.

--- gcc/tree-ssa-phiprop.c.jj	2017-05-22 10:50:11.000000000 +0200
+++ gcc/tree-ssa-phiprop.c	2017-07-11 16:52:41.012340615 +0200
@@ -327,7 +327,7 @@ propagate_with_phi (basic_block bb, gphi
       if (!dominated_by_p (CDI_POST_DOMINATORS,
 			   bb, gimple_bb (use_stmt)))
 	continue;
-         
+
       /* Check whether this is a load of *ptr.  */
       if (!(is_gimple_assign (use_stmt)
 	    && gimple_assign_rhs_code (use_stmt) == MEM_REF
@@ -356,6 +356,9 @@ propagate_with_phi (basic_block bb, gphi
          insert aggregate copies on the edges instead.  */
       if (!is_gimple_reg_type (TREE_TYPE (TREE_TYPE (ptr))))
 	{
+	  if (!gimple_vdef (use_stmt))
+	    goto next;
+
 	  /* As we replicate the lhs on each incoming edge all
 	     used SSA names have to be available there.  */
 	  if (! for_each_index (gimple_assign_lhs_ptr (use_stmt),
@@ -363,6 +366,51 @@ propagate_with_phi (basic_block bb, gphi
 				get_immediate_dominator (CDI_DOMINATORS,
 							 gimple_bb (phi))))
 	    goto next;
+
+	  gimple *vuse_stmt;
+	  imm_use_iterator vui;
+	  use_operand_p vuse_p;
+	  bool debug_use_seen = false;
+	  /* In order to move the aggregate copies earlier, make sure
+	     there are no statements that could read from memory
+	     aliasing the lhs in between the start of bb and use_stmt.
+	     As we require use_stmt to have a VDEF above, loads after
+	     use_stmt will use a different virtual SSA_NAME.  */
+	  FOR_EACH_IMM_USE_FAST (vuse_p, vui, vuse)
+	    {
+	      vuse_stmt = USE_STMT (vuse_p);
+	      if (vuse_stmt == use_stmt)
+		continue;
+	      if (!dominated_by_p (CDI_DOMINATORS,
+				   gimple_bb (vuse_stmt), bb))
+		continue;
+	      if (ref_maybe_used_by_stmt_p (vuse_stmt,
+					    gimple_assign_lhs (use_stmt)))
+		{
+		  if (is_gimple_debug (vuse_stmt))
+		    debug_use_seen = true;
+		  else
+		    goto next;
+		}
+	    }
+	  /* Debug stmt uses should not prevent the transformation, but
+	     if we saw any, reset those debug stmts.  */
+	  if (debug_use_seen)
+	    FOR_EACH_IMM_USE_STMT (vuse_stmt, vui, vuse)
+	      {
+		if (!is_gimple_debug (vuse_stmt))
+		  continue;
+		if (!dominated_by_p (CDI_DOMINATORS,
+				     gimple_bb (vuse_stmt), bb))
+		  continue;
+		if (ref_maybe_used_by_stmt_p (vuse_stmt,
+					      gimple_assign_lhs (use_stmt)))
+		  {
+		    gimple_debug_bind_reset_value (vuse_stmt);
+		    update_stmt (vuse_stmt);
+		  }
+	      }
+
 	  phiprop_insert_phi (bb, phi, use_stmt, phivn, n);
 
 	  /* Remove old stmt.  The phi is taken care of by DCE.  */
--- gcc/testsuite/g++.dg/torture/pr81365.C.jj	2017-07-11 17:07:11.107130111 +0200
+++ gcc/testsuite/g++.dg/torture/pr81365.C	2017-07-11 17:06:52.000000000 +0200
@@ -0,0 +1,39 @@
+// PR tree-optimization/81365
+// { dg-do run }
+
+struct A { unsigned a; };
+
+struct B {
+  B (const A *x)
+  {
+    __builtin_memcpy (b, x, 3 * sizeof (A));
+    __builtin_memcpy (c, x + 3, sizeof (A));
+    __builtin_memset (c + 1, 0, sizeof (A));
+  }
+  bool
+  foo (unsigned x)
+  {
+    A *it = c;
+    if (it->a == x || (++it)->a == x)
+      {
+	A t(b[0]);
+	b[0] = *it;
+	*it = t;
+	return true;
+      }
+    return false;
+  }
+  A b[3];
+  A c[2];
+};
+
+int
+main ()
+{
+  A x[] = { 4, 8, 12, 18 };
+  B y(x);
+  if (!y.foo (18))
+    __builtin_abort ();
+  if (!y.foo (4))
+    __builtin_abort ();
+}

	Jakub