From 86efb5cd550babd6bf69ead21cc73f0012c55a97 Mon Sep 17 00:00:00 2001
From: Jakub Jelinek <jakub@redhat.com>
Date: Tue, 5 Mar 2013 07:04:14 +0100
Subject: 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/simplify-rtx.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

(limited to 'gcc/simplify-rtx.c')

diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
index 3f04b8b..43700cf 100644
--- a/gcc/simplify-rtx.c
+++ b/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)
-- 
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