From: Richard Stallman <rms@gnu.org>
Date: Fri, 28 May 1993 22:40:33 +0000 (+0000)
Subject: (fold_rtx): Correct check for associating shifts and ending up with a shift count... 
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=4908e5087063c4b310ab617e09230ad65f294efa;p=gcc.git

(fold_rtx): Correct check for associating shifts and ending up with a shift count too large...

(fold_rtx): Correct check for associating shifts and
ending up with a shift count too large; convert to the
largest valid for ASHIFTRT and don't fold all others.

From-SVN: r4585
---

diff --git a/gcc/cse.c b/gcc/cse.c
index 3d2702fbbe3..8ae97142760 100644
--- a/gcc/cse.c
+++ b/gcc/cse.c
@@ -5283,13 +5283,21 @@ fold_rtx (x, insn)
 		break;
 
 	      /* If we are associating shift operations, don't let this
-		 produce a shift of larger than the object.  This could
-		 occur when we following a sign-extend by a right shift on
-		 a machine that does a sign-extend as a pair of shifts.  */
+		 produce a shift of the size of the object or larger.
+		 This could occur when we follow a sign-extend by a right
+		 shift on a machine that does a sign-extend as a pair
+		 of shifts.  */
 
 	      if (is_shift && GET_CODE (new_const) == CONST_INT
-		  && INTVAL (new_const) > GET_MODE_BITSIZE (mode))
-		break;
+		  && INTVAL (new_const) >= GET_MODE_BITSIZE (mode))
+		{
+		  /* As an exception, we can turn an ASHIFTRT of this
+		     form into a shift of the number of bits - 1.  */
+		  if (code == ASHIFTRT)
+		    new_const = GEN_INT (GET_MODE_BITSIZE (mode) - 1);
+		  else
+		    break;
+		}
 
 	      y = copy_rtx (XEXP (y, 0));