[PATCH] Don't transform virtual PHIs into COND_EXPRs in tree ifcvt (PR tree-optimization/34140)

[Jakub Jelinek]

Hi!

On the attached testcase loop unswitching creates from admitedly
superfluous virtual PHI:
  # tD.1550_45 = PHI <tD.1550_47(13), tD.1550_47(11)>
  # tD.1550_46 = VDEF <tD.1550_45> { tD.1550 }
  tD.1550.tD.1542[iD.1549_43].sD.1540 = prephitmp.14D.1578_44;
created by loop unswitching a COND_EXPR, which is not valid
gimple:
tD.1550_45 = D.1561_49 != 0 ? tD.1550_47 : tD.1550_47;
(t is an aggregate).  While perhaps loop unswitching should be fixed not to
create PHIs with all args identical, I believe various other optimizations
can create these and even if it would be desirable to optimize them out,
we probably wouldn't do it after every pass, so I think the primary
bug is on the tree-if-conv.c side.  Only non-virtual PHIs can be really
converted, and as all PHIs on BBs other than loop header must be converted,
we should IMHO just not if-convert such loops.

I have tested that on no make check testcase other than the newly added one
we hit this.  Bootstrap/regression testing on x86_64-linux pending, ok
for trunk if it succeeds?

2007-11-28  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/34140
	* tree-if-conv.c (if_convertible_phi_p): Fail if BB other than
	loop->header has virtual phi nodes.

	* gcc.c-torture/compile/20071128-1.c: New test.

--- gcc/tree-if-conv.c.jj	2007-11-02 19:02:47.000000000 +0100
+++ gcc/tree-if-conv.c	2007-11-28 13:15:37.000000000 +0100
@@ -302,7 +302,8 @@ tree_if_convert_cond_expr (struct loop *
    and it belongs to basic block BB.
    PHI is not if-convertible
    - if it has more than 2 arguments.
-   - Virtual PHI is immediately used in another PHI node.  */
+   - Virtual PHI is immediately used in another PHI node.
+   - Virtual PHI on BB other than header.  */
 
 static bool
 if_convertible_phi_p (struct loop *loop, basic_block bb, tree phi)
@@ -324,6 +325,13 @@ if_convertible_phi_p (struct loop *loop,
     {
       imm_use_iterator imm_iter;
       use_operand_p use_p;
+
+      if (bb != loop->header)
+	{
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    fprintf (dump_file, "Virtual phi not on loop header.\n");
+	  return false;
+	}
       FOR_EACH_IMM_USE_FAST (use_p, imm_iter, PHI_RESULT (phi))
 	{
 	  if (TREE_CODE (USE_STMT (use_p)) == PHI_NODE)
--- gcc/testsuite/gcc.c-torture/compile/20071128-1.c.jj	2007-11-28 13:32:06.000000000 +0100
+++ gcc/testsuite/gcc.c-torture/compile/20071128-1.c	2007-11-28 13:45:27.000000000 +0100
@@ -0,0 +1,24 @@
+/* PR tree-optimization/34140 */
+/* Testcase by Martin Michlmayr <tbm@cyrius.com> */
+
+struct S
+{
+  unsigned int s;
+};
+struct T
+{
+  struct S t[2];
+  unsigned int u : 1;
+};
+
+void
+foo (int x, int y, int z)
+{
+  int i;
+  struct T t;
+
+  t.u = t.u;
+  for (i = 0; i < x; i++)
+    if (z != 1)
+      t.t[i].s = y || t.u;
+}

	Jakub