[PATCH] Fix up get_reload_reg (PR rtl-optimization/56195)

[Jakub Jelinek]

Hi!

As the following testcase shows, get_reload_reg could sometimes return
a reused reg in a wrong mode.  If curr_insn_input_reloads[i].input
and original have VOIDmode, they could compare equal (same integer
constant), yet mode might be different from
GET_MODE (curr_insn_input_reloads[i].reg).
If we need a wider reg than we already have, we can't reuse it easily,
but if we need a narrower one, we can just use a subreg of the wider one.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2013-02-07  Jakub Jelinek  <ja...@redhat.com>

        PR rtl-optimization/56195
        * lra-constraints.c (get_reload_reg): Don't reuse regs
        if they have smaller mode than requested, if they have
        wider mode than requested, try to return a SUBREG.

        * gcc.dg/torture/pr56195.c: New test.

--- gcc/lra-constraints.c.jj    2013-02-07 18:34:39.000000000 +0100
+++ gcc/lra-constraints.c       2013-02-07 20:58:25.558920536 +0100
@@ -421,8 +421,20 @@ get_reload_reg (enum op_type type, enum
       if (rtx_equal_p (curr_insn_input_reloads[i].input, original)
          && in_class_p (curr_insn_input_reloads[i].reg, rclass, &new_class))
        {
-         *result_reg = curr_insn_input_reloads[i].reg;
-         regno = REGNO (*result_reg);
+         rtx reg = curr_insn_input_reloads[i].reg;
+         regno = REGNO (reg);
+         /* If input is equal to original and both are VOIDmode,
+            GET_MODE (reg) might be still different from mode.
+            Ensure we don't return *result_reg with wrong mode.  */
+         if (GET_MODE (reg) != mode)
+           {
+             if (GET_MODE_SIZE (GET_MODE (reg)) < GET_MODE_SIZE (mode))
+               continue;
+             reg = lowpart_subreg (mode, reg, GET_MODE (reg));
+             if (reg == NULL_RTX || GET_CODE (reg) != SUBREG)
+               continue;
+           }
+         *result_reg = reg;
          if (lra_dump_file != NULL)
            {
              fprintf (lra_dump_file, "  Reuse r%d for reload ", regno);
--- gcc/testsuite/gcc.dg/torture/pr56195.c.jj   2013-02-07 21:08:34.244334032 
+0100
+++ gcc/testsuite/gcc.dg/torture/pr56195.c      2013-02-07 21:08:18.000000000 
+0100
@@ -0,0 +1,31 @@
+/* PR rtl-optimization/56195 */
+/* { dg-do assemble } */
+
+int i, a, t, b, c, d, e, f, j, *h;
+
+void
+fn (void)
+{
+  if (b)
+    {
+      int *p, *q;
+      char g;
+
+      if (f++)
+       for (;; e++);
+    lbl:
+      for (b = 0; b < 2; b++)
+       t /= d + 1 ? : i || a < c < (d = f) ? : 1 | (j = 2);
+
+      *p = g >= *q ^ c != a ^ *p;
+
+      if (!e)
+       {
+         q = p;
+         goto lbl;
+       }
+    }
+
+  if (h++)
+    goto lbl;
+}

        Jakub