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


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  <jakub@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


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