From: Richard Henderson <rth@cygnus.com>
Date: Thu, 26 Mar 1998 00:20:08 +0000 (-0800)
Subject: * combine.c (make_compound_operation): Simplify (subreg (*_extend) 0).
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=6f28d3e98257593850baca079e60a59eae47bc9f;p=gcc.git

* combine.c (make_compound_operation): Simplify (subreg (*_extend) 0).

From-SVN: r18836
---

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index dddc848c105..028e157752c 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,7 @@
+Thu Mar 26 00:19:47 1998  Richard Henderson  <rth@cygnus.com>
+
+	* combine.c (make_compound_operation): Simplify (subreg (*_extend) 0).
+
 Wed Mar 25 23:53:11 1998  Jeffrey A Law  (law@cygnus.com)
 
 	* pa.c (pa_adjust_cost): Avoid redundant calls to get_attr_type.
diff --git a/gcc/combine.c b/gcc/combine.c
index 8cb32dc67c6..4bef563f1b8 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -6038,6 +6038,23 @@ make_compound_operation (x, in_code)
 
 	  return newer;
 	}
+
+      /* If this is a paradoxical subreg, and the new code is a sign or
+	 zero extension, omit the subreg and widen the extension.  If it
+	 is a regular subreg, we can still get rid of the subreg by not
+	 widening so much, or in fact removing the extension entirely.  */
+      if ((GET_CODE (tem) == SIGN_EXTEND
+	   || GET_CODE (tem) == ZERO_EXTEND)
+	  && subreg_lowpart_p (x))
+	{
+	  if (GET_MODE_SIZE (mode) > GET_MODE_SIZE (GET_MODE (tem))
+	      || (GET_MODE_SIZE (mode) >
+		  GET_MODE_SIZE (GET_MODE (XEXP (tem, 0)))))
+	    tem = gen_rtx_combine (GET_CODE (tem), mode, XEXP (tem, 0));
+	  else
+	    tem = gen_lowpart_for_combine (mode, XEXP (tem, 0));
+	  return tem;
+	}
       break;
       
     default: