[PATCH] Fix UB in shrink-wrapping (PR rtl-optimization/85167)

[Richard Biener]

On April 3, 2018 6:07:17 PM GMT+02:00, Jakub Jelinek <jakub@redhat.com> wrote:
>Hi!
>
>The bb_uses and bb_defs bitmaps are never used if !*split_p, the
>comments
>even describe why:
>  /* For the new created basic block, there is no dataflow info at all.
>     So skip the following dataflow update and check.  */
>On the new bb in that case DF_LR_BB_INFO is NULL, so &(NULL->field) is
>UB.
>Fixed thusly, the NULL init added there just in case uninit can't
>figure it
>out in some bootstrap mode.
>
>Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

OK. 

Richard. 

>2018-04-03  Jakub Jelinek  <jakub@redhat.com>
>
>	PR rtl-optimization/85167
>	* shrink-wrap.c (move_insn_for_shrink_wrap): Don't set bb_uses and
>	bb_defs if *split_p, instead preinitialize it to NULL.
>
>	* gcc.dg/pr85167.c: New test.
>
>--- gcc/shrink-wrap.c.jj	2018-02-10 00:21:18.284975396 +0100
>+++ gcc/shrink-wrap.c	2018-04-03 13:06:54.183464995 +0200
>@@ -157,7 +157,7 @@ move_insn_for_shrink_wrap (basic_block b
> 			   struct dead_debug_local *debug)
> {
>   rtx set, src, dest;
>-  bitmap live_out, live_in, bb_uses, bb_defs;
>+  bitmap live_out, live_in, bb_uses = NULL, bb_defs = NULL;
>   unsigned int i, dregno, end_dregno;
>   unsigned int sregno = FIRST_PSEUDO_REGISTER;
>   unsigned int end_sregno = FIRST_PSEUDO_REGISTER;
>@@ -330,8 +330,11 @@ move_insn_for_shrink_wrap (basic_block b
>       /* Check whether BB uses DEST or clobbers DEST.  We need to add
> 	 INSN to BB if so.  Either way, DEST is no longer live on entry,
> 	 except for any part that overlaps SRC (next loop).  */
>-      bb_uses = &DF_LR_BB_INFO (bb)->use;
>-      bb_defs = &DF_LR_BB_INFO (bb)->def;
>+      if (!*split_p)
>+	{
>+	  bb_uses = &DF_LR_BB_INFO (bb)->use;
>+	  bb_defs = &DF_LR_BB_INFO (bb)->def;
>+	}
>       if (df_live)
> 	{
> 	  for (i = dregno; i < end_dregno; i++)
>--- gcc/testsuite/gcc.dg/pr85167.c.jj	2018-04-03 13:14:13.532523126
>+0200
>+++ gcc/testsuite/gcc.dg/pr85167.c	2018-04-03 13:08:36.883478590 +0200
>@@ -0,0 +1,16 @@
>+/* PR rtl-optimization/85167 */
>+/* { dg-do compile } */
>+/* { dg-options "-O2 -w" } */
>+
>+struct A { long b; };
>+int c, d, e;
>+int bar (void);
>+
>+int
>+foo (void)
>+{
>+  long g;
>+  for (; g == c ? 0 : (e = 1); g = ((struct A *)g)->b)
>+    if (bar ())
>+      return d;
>+}
>
>	Jakub