combine.c (force_to_mode): Handle TRUNCATE.

	* combine.c (force_to_mode): Handle TRUNCATE.  Factor out
	truncation from operands in binary operations.

testsuite/
	* gcc.target/mips/truncate-4.c: New testcase.

From-SVN: r149154

1 files changed, 18 insertions, 6 deletions

diff --git a/gcc/combine.c b/gcc/combine.c
index b8c080c..a4f0d66 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -7358,6 +7358,10 @@ force_to_mode (rtx x, enum machine_mode mode, unsigned HOST_WIDE_INT mask,
 	return force_to_mode (SUBREG_REG (x), mode, mask, next_select);
       break;
 
+    case TRUNCATE:
+      /* Similarly for a truncate.  */
+      return force_to_mode (XEXP (x, 0), mode, mask, next_select);
+
     case AND:
       /* If this is an AND with a constant, convert it into an AND
 	 whose constant is the AND of that constant with MASK.  If it
@@ -7502,12 +7506,20 @@ force_to_mode (rtx x, enum machine_mode mode, unsigned HOST_WIDE_INT mask,
       /* For most binary operations, just propagate into the operation and
 	 change the mode if we have an operation of that mode.  */
 
-      op0 = gen_lowpart_or_truncate (op_mode,
-				     force_to_mode (XEXP (x, 0), mode, mask,
-						    next_select));
-      op1 = gen_lowpart_or_truncate (op_mode,
-				     force_to_mode (XEXP (x, 1), mode, mask,
-					next_select));
+      op0 = force_to_mode (XEXP (x, 0), mode, mask, next_select);
+      op1 = force_to_mode (XEXP (x, 1), mode, mask, next_select);
+
+      /* If we ended up truncating both operands, truncate the result of the
+	 operation instead.  */
+      if (GET_CODE (op0) == TRUNCATE
+	  && GET_CODE (op1) == TRUNCATE)
+	{
+	  op0 = XEXP (op0, 0);
+	  op1 = XEXP (op1, 0);
+	}
+
+      op0 = gen_lowpart_or_truncate (op_mode, op0);
+      op1 = gen_lowpart_or_truncate (op_mode, op1);
 
       if (op_mode != GET_MODE (x) || op0 != XEXP (x, 0) || op1 != XEXP (x, 1))
 	x = simplify_gen_binary (code, op_mode, op0, op1);