Fix a cfgcleanup head-merge issue on cc0 targets

[Bernd Schmidt]

This showed up with a coldfire-linux toolchain. get_condition can return
NULL in some cases when the condition is reversed and there are float
modes involved; in that case we will move instructions in between a cc0
user and setter.

This patch fixes it. Tested on cris-elf, since I currently have no way
of testing m68k. Will commit as obvious tomorrow if no objections.


Bernd

        * cfgcleanup.c (try_head_merge_bb): If get_condition returns
        NULL for a jump that is a cc0 insn, pick the previous insn for
        move_before.

        * gcc.c-torture/compile/20110907.c: New file.

Index: gcc/cfgcleanup.c
===================================================================
--- gcc/cfgcleanup.c    (revision 178596)
+++ gcc/cfgcleanup.c    (working copy)
@@ -2214,7 +2214,14 @@ try_head_merge_bb (basic_block bb)
 
   cond = get_condition (jump, &move_before, true, false);
   if (cond == NULL_RTX)
-    move_before = jump;
+    {
+#ifdef HAVE_cc0
+      if (reg_mentioned_p (cc0_rtx, jump))
+       move_before = prev_nonnote_nondebug_insn (jump);
+      else
+#endif
+       move_before = jump;
+    }
 
   for (ix = 0; ix < nedges; ix++)
     if (EDGE_SUCC (bb, ix)->dest == EXIT_BLOCK_PTR)
@@ -2376,7 +2383,14 @@ try_head_merge_bb (basic_block bb)
       jump = BB_END (final_dest_bb);
       cond = get_condition (jump, &move_before, true, false);
       if (cond == NULL_RTX)
-       move_before = jump;
+       {
+#ifdef HAVE_cc0
+         if (reg_mentioned_p (cc0_rtx, jump))
+           move_before = prev_nonnote_nondebug_insn (jump);
+         else
+#endif
+           move_before = jump;
+       }
     }
 
   do
Index: gcc/testsuite/gcc.c-torture/compile/20110907.c
===================================================================
--- gcc/testsuite/gcc.c-torture/compile/20110907.c      (revision 0)
+++ gcc/testsuite/gcc.c-torture/compile/20110907.c      (revision 0)
@@ -0,0 +1,26 @@
+struct ieee754_double {
+  double d;
+};
+extern const float __exp_deltatable[178];
+float __ieee754_expf (float x)
+{
+  static const float himark = 88.72283935546875;
+  static const float lomark = -103.972084045410;
+  if (__builtin_isless(x, himark) && __builtin_isgreater(x, lomark))
+    {
+      int tval;
+      double x22, t, result, dx;
+      float delta;
+      struct ieee754_double ex2_u;
+      dx -= t;
+      tval = (int) (t * 512.0);
+      if (t >= 0)
+       delta = - __exp_deltatable[tval];
+      else
+       delta = __exp_deltatable[-tval];
+      x22 = (0.5000000496709180453 * dx + 1.0000001192102037084) * dx + delta;
+      result = x22 * ex2_u.d + ex2_u.d;
+      return (float) result;
+    }
+  return x;
+}