emit-rtl.c (copy_rtx_if_shared): A MEM which references virtual_stack_vars_rtx…

emit-rtl.c (copy_rtx_if_shared): A MEM which references virtual_stack_vars_rtx or virtual_incoming_args_rtx can...

        * emit-rtl.c (copy_rtx_if_shared): A MEM which references
        virtual_stack_vars_rtx or virtual_incoming_args_rtx can not
        be shared.

From-SVN: r29001

gcc/ChangeLog

@@ -42,10 +42,6 @@ Mon Aug 30 16:07:49 1999  Richard Henderson  <rth@cygnus.com>
 	* flow.c (new_insn_dead_notes): Use sets_reg_or_subreg not
 	mark_set_resources.
 
-Mon Aug 30 16:36:33 1999  Jeffrey A Law  (law@cygnus.com)
-
-	* invoke.texi: Fix typo.
-
 Mon Aug 30 12:23:53 1999  Jim Wilson  <wilson@cygnus.com>
 
 	* fixinc/Makefile.in (subdir): New.
@@ -54,6 +50,12 @@ Mon Aug 30 12:23:53 1999  Jim Wilson  <wilson@cygnus.com>
 	
 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.
+
+	* invoke.texi: Fix typo.
+
 	* dwarf2out.c (mem_loc_descriptor): New argument MODE.  All callers
 	changed.  Handle autoincrement addressing modes.
 

gcc/emit-rtl.c

@@ -1678,16 +1678,18 @@ 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,