Remove noce_mem_write_may_trap_or_fault_p in ifcvt

[Bernd Schmidt <bernds_cb1 at t-online dot de>]

The ifcvt scratchpad patch had some modifications to the function 
noce_mem_write_may_trap_or_fault_p in ifcvt, but as far as I can tell, 
that function itself makes no sense whatsoever. It returns true for 
MEM_READONLY_P which is sensible, but then it also goes on an unreliable 
search through the address, looking for SYMBOL_REFs that are in 
decl_readonly_section. Needless to say, this won't ever find anything on 
targets that don't allow symbolic addresses, and is not reliable even on 
targets that do. The MEM_READONLY_P test must suffice; if there's a 
reason why it doesn't, we'd need to figure out why and possibly disable 
if-conversion of stores more thoroughly.

As a sanity check I bootstrapped and tested the first of the two 
attached patches, which changes the "return true" paths to 
gcc_unreachable. Since that passed, I propose the second of the two 
attached patches, which removes the function and replaces it with a 
simpler check. Ok if that passes too?


Bernd

Index: gcc/ifcvt.c
===================================================================
--- gcc/ifcvt.c	(revision 229049)
+++ gcc/ifcvt.c	(working copy)
@@ -2868,11 +2868,12 @@ noce_mem_write_may_trap_or_fault_p (cons
 	  return false;
 	break;
       case LABEL_REF:
-	return true;
+	gcc_unreachable ();
       case SYMBOL_REF:
 	if (SYMBOL_REF_DECL (addr)
 	    && decl_readonly_section (SYMBOL_REF_DECL (addr), 0))
-	  return true;
+	  gcc_unreachable ();
+
 	return false;
       default:
 	return false;

	* ifcvt.c (noce_mem_write_may_trap_or_fault_p): Delete function.
	(noce_process_if_block): Don't call it, test MEM_READONLY_P and
	may_trap_or_fault_p instead.

Index: gcc/ifcvt.c
===================================================================
--- gcc/ifcvt.c	(revision 229049)
+++ gcc/ifcvt.c	(working copy)
@@ -2828,59 +2828,6 @@ noce_operand_ok (const_rtx op)
   return ! may_trap_p (op);
 }
 
-/* Return true if a write into MEM may trap or fault.  */
-
-static bool
-noce_mem_write_may_trap_or_fault_p (const_rtx mem)
-{
-  rtx addr;
-
-  if (MEM_READONLY_P (mem))
-    return true;
-
-  if (may_trap_or_fault_p (mem))
-    return true;
-
-  addr = XEXP (mem, 0);
-
-  /* Call target hook to avoid the effects of -fpic etc....  */
-  addr = targetm.delegitimize_address (addr);
-
-  while (addr)
-    switch (GET_CODE (addr))
-      {
-      case CONST:
-      case PRE_DEC:
-      case PRE_INC:
-      case POST_DEC:
-      case POST_INC:
-      case POST_MODIFY:
-	addr = XEXP (addr, 0);
-	break;
-      case LO_SUM:
-      case PRE_MODIFY:
-	addr = XEXP (addr, 1);
-	break;
-      case PLUS:
-	if (CONST_INT_P (XEXP (addr, 1)))
-	  addr = XEXP (addr, 0);
-	else
-	  return false;
-	break;
-      case LABEL_REF:
-	return true;
-      case SYMBOL_REF:
-	if (SYMBOL_REF_DECL (addr)
-	    && decl_readonly_section (SYMBOL_REF_DECL (addr), 0))
-	  return true;
-	return false;
-      default:
-	return false;
-      }
-
-  return false;
-}
-
 /* Return whether we can use store speculation for MEM.  TOP_BB is the
    basic block above the conditional block where we are considering
    doing the speculative store.  We look for whether MEM is set
@@ -3210,7 +3157,8 @@ noce_process_if_block (struct noce_if_in
 	 THEN and ELSE arms, then we can go ahead with the conversion;
 	 either the program is broken, or the condition is always
 	 false such that the other memory is selected.  */
-      if (noce_mem_write_may_trap_or_fault_p (orig_x))
+      if (may_trap_or_fault_p (orig_x)
+	  || MEM_READONLY_P (orig_x))
 	return FALSE;
 
       /* Avoid store speculation: given "if (...) x = a" where x is a