re PR rtl-optimization/56494 (ICE in simplify_truncation, at simplify-rtx.c:619)

	PR rtl-optimization/56494
	* simplify-rtx.c (simplify_truncation): If C is narrower than A,
	optimize (truncate:A (subreg:B (truncate:C X) 0)) into
	(subreg:A (truncate:C X) 0) instead of (truncate:A X).

	* gcc.dg/pr56494.c: New test.

From-SVN: r196451

gcc/ChangeLog

 2013-03-05  Jakub Jelinek  <jakub@redhat.com>
 
+	PR rtl-optimization/56494
+	* simplify-rtx.c (simplify_truncation): If C is narrower than A,
+	optimize (truncate:A (subreg:B (truncate:C X) 0)) into
+	(subreg:A (truncate:C X) 0) instead of (truncate:A X).
+
 	PR middle-end/56461
 	* sel-sched-ir.c (free_sched_pools): Release
 	succs_info_pool.stack[succs_info_pool.max_top] vectors too

gcc/simplify-rtx.c

@@ -757,8 +757,17 @@ simplify_truncation (enum machine_mode mode, rtx op,
       && SCALAR_INT_MODE_P (GET_MODE (SUBREG_REG (op)))
       && GET_CODE (SUBREG_REG (op)) == TRUNCATE
       && subreg_lowpart_p (op))
-    return simplify_gen_unary (TRUNCATE, mode, XEXP (SUBREG_REG (op), 0),
-			       GET_MODE (XEXP (SUBREG_REG (op), 0)));
+    {
+      rtx inner = XEXP (SUBREG_REG (op), 0);
+      if (GET_MODE_PRECISION (mode)
+	  <= GET_MODE_PRECISION (GET_MODE (SUBREG_REG (op))))
+	return simplify_gen_unary (TRUNCATE, mode, inner, GET_MODE (inner));
+      else
+	/* If subreg above is paradoxical and C is narrower
+	   than A, return (subreg:A (truncate:C X) 0).  */
+	return simplify_gen_subreg (mode, SUBREG_REG (op),
+				    GET_MODE (SUBREG_REG (op)), 0);
+    }
 
   /* (truncate:A (truncate:B X)) is (truncate:A X).  */
   if (GET_CODE (op) == TRUNCATE)

gcc/testsuite/ChangeLog

+2013-03-05  Jakub Jelinek  <jakub@redhat.com>
+
+	PR rtl-optimization/56494
+	* gcc.dg/pr56494.c: New test.
+
 2013-01-04  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* gcc.dg/pr56424.c: New test.

gcc/testsuite/gcc.dg/pr56494.c

+/* PR rtl-optimization/56494 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -ftracer -w" } */
+
+char a;
+short b;
+void bar (int);
+
+void
+foo (void)
+{
+  bar ((!!b ? : (a *= a / 0)) >= (a = b));
+}