From: Bernd Schmidt <bernds@redhat.co.uk>
Date: Mon, 18 Dec 2000 14:37:37 +0000 (+0000)
Subject: Backport a fix that restricts sharing of some MEMs.
X-Git-Tag: prereleases/gcc-2.95.3-test1~27
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=860480e60ce6201847bcfc13b23bc374c5f035b8;p=thirdparty%2Fgcc.git

Backport a fix that restricts sharing of some MEMs.

From-SVN: r38350
---

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 9ced870d7e60..7334ad2af7de 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,10 @@
 2000-12-18  Bernd Schmidt  <bernds@redhat.co.uk>
 
+	Mon Aug 30 01:02:09 1999  Jeffrey A Law  (law@cygnus.com)
+	* emit-rtl.c (copy_rtx_if_shared): A MEM which references
+	virtual_stack_vars_rtx or virtual_incoming_args_rtx can not
+	be shared.
+
 	2000-03-24  Geoff Keating  <geoffk@cygnus.com>
 	* flow.c (propagate_block): When we delete an ADDR_VEC,
 	also delete the BARRIER following it if there is one.
diff --git a/gcc/emit-rtl.c b/gcc/emit-rtl.c
index 222a1a937f09..54cee163738a 100644
--- a/gcc/emit-rtl.c
+++ b/gcc/emit-rtl.c
@@ -1847,25 +1847,17 @@ copy_rtx_if_shared (orig)
       return x;
 
     case MEM:
-      /* A MEM is allowed to be shared if its address is constant
-	 or is a constant plus one of the special registers.  */
-      if (CONSTANT_ADDRESS_P (XEXP (x, 0))
-	  || XEXP (x, 0) == virtual_stack_vars_rtx
-	  || XEXP (x, 0) == virtual_incoming_args_rtx)
+      /* A MEM is allowed to be shared if its address is constant.
+
+	 We used to allow sharing of MEMs which referenced 
+	 virtual_stack_vars_rtx or virtual_incoming_args_rtx, but
+	 that can lose.  instantiate_virtual_regs will not unshare
+	 the MEMs, and combine may change the structure of the address
+	 because it looks safe and profitable in one context, but
+	 in some other context it creates unrecognizable RTL.  */
+      if (CONSTANT_ADDRESS_P (XEXP (x, 0)))
 	return x;
 
-      if (GET_CODE (XEXP (x, 0)) == PLUS
-	  && (XEXP (XEXP (x, 0), 0) == virtual_stack_vars_rtx
-	      || XEXP (XEXP (x, 0), 0) == virtual_incoming_args_rtx)
-	  && CONSTANT_ADDRESS_P (XEXP (XEXP (x, 0), 1)))
-	{
-	  /* This MEM can appear in more than one place,
-	     but its address better not be shared with anything else.  */
-	  if (! x->used)
-	    XEXP (x, 0) = copy_rtx_if_shared (XEXP (x, 0));
-	  x->used = 1;
-	  return x;
-	}
       break;
 
     default: