Re: Remove noce_mem_write_may_trap_or_fault_p in ifcvt

[Bernd Schmidt <bschmidt at redhat dot com>]

On 11/25/2015 04:00 PM, Jakub Jelinek wrote:
> nonfreeing_call_p is one necessary condition (if that is true, it means
> the call could mean that the first access does not trap while the second one
> does).
> But I agree that we need a predicate for nonbarrier_call_p or similar.
> Some atomic builtins are not barriers though and IMHO should not be treated
> as such, at least relaxed atomic loads/stores and pehraps even other relaxed
> atomics.  And it would be nice to have IPA discovery of nonbarrier_call_p
> calls, like we have for nonfreeing_fn.

So here's a very basic version which I think is appropriate for the 
current stage, and can be extended later. Ok if it passes testing?


Bernd

diff --git a/gcc/gimple.c b/gcc/gimple.c
index 2764df8..bf552a7 100644
--- a/gcc/gimple.c
+++ b/gcc/gimple.c
@@ -2636,6 +2636,18 @@ nonfreeing_call_p (gimple *call)
   return n->nonfreeing_fn;
 }
 
+/* Return true when CALL is a call stmt that definitely need not
+   be considered to be a memory barrier.  */
+bool
+nonbarrier_call_p (gimple *call)
+{
+  if (gimple_call_flags (call) & (ECF_PURE | ECF_CONST))
+    return true;
+  /* Should extend this to have a nonbarrier_fn flag, just as above in
+     the nonfreeing case.  */
+  return false;
+}
+
 /* Callback for walk_stmt_load_store_ops.
  
    Return TRUE if OP will dereference the tree stored in DATA, FALSE
diff --git a/gcc/gimple.h b/gcc/gimple.h
index 6eb22de..0b04804 100644
--- a/gcc/gimple.h
+++ b/gcc/gimple.h
@@ -1507,6 +1507,7 @@ extern bool gimple_call_builtin_p (const gimple *, enum built_in_function);
 extern bool gimple_asm_clobbers_memory_p (const gasm *);
 extern void dump_decl_set (FILE *, bitmap);
 extern bool nonfreeing_call_p (gimple *);
+extern bool nonbarrier_call_p (gimple *);
 extern bool infer_nonnull_range (gimple *, tree);
 extern bool infer_nonnull_range_by_dereference (gimple *, tree);
 extern bool infer_nonnull_range_by_attribute (gimple *, tree);
diff --git a/gcc/tree-ssa-phiopt.c b/gcc/tree-ssa-phiopt.c
index 02d5aa0..56b3732 100644
--- a/gcc/tree-ssa-phiopt.c
+++ b/gcc/tree-ssa-phiopt.c
@@ -1519,7 +1519,10 @@ nontrapping_dom_walker::before_dom_children (basic_block bb)
     {
       gimple *stmt = gsi_stmt (gsi);
 
-      if (is_gimple_call (stmt) && !nonfreeing_call_p (stmt))
+      if (gimple_code (stmt) == GIMPLE_ASM
+	  || (is_gimple_call (stmt)
+	      && (!nonfreeing_call_p (stmt)
+		  || !nonbarrier_call_p (stmt))))
 	nt_call_phase++;
       else if (gimple_assign_single_p (stmt) && !gimple_has_volatile_ops (stmt))
 	{