Re: New post-LTO OpenACC pass

[Nathan Sidwell <nathan at acm dot org>]

On 09/25/15 06:28, Bernd Schmidt wrote:

> This is the c-c++-common/goacc/acc_on_device-2.c testcase. Is that expected to
> be handled? If I change it to use __builtin_acc_on_device, I can step right into
>
> Breakpoint 8, fold_call_stmt (stmt=0x7ffff0736e10, ignore=false) at
> ../../git/gcc/builtins.c:12277
> 12277      tree ret = NULL_TREE;
>
> Maybe you were compiling without optimization? In that case
> expand_builtin_acc_on_device (which already exists) should still end up doing
> the right thing. In no case should you see a RTL call to a function, that
> indicates that something else went wrong.

I think I was reading more into the std than it intended, as it claims 
on_deveice should evaluate 'to a constant'.  (no mention of 'when optimizing'). 
 It can't mean 'be useable in integral-constant-expression, as at the point we 
 need those, one doesn't know the value it should be.

thinking about it, I don't think a user can tell.  the case I had in mind (and 
have used it for), is something like

on_device (nvidia)  ? asm ("NVIDIA specific asm") : c-expr

and for that to work, one must turn the optimzer on to get the dead code 
removal, regardless of where on_device expands.  So my goal of  getting it 
expanded regardless of optimization level is not needed --- indeed getting it 
expanded in fold_call_stmt will mean the body of expand_on_device can go away (I 
think).

From the POV of what the programmer really cares about is that when optimizing 
the compiler  knows how to fold it.

> Can you send me the patch you tried (and possibly a testcase you expect to be
> handled), I'll see if I can find out what's going on.

Thanks!  When things didn't work, I tried getting it workong on the gomp4 
branch, as I new what to expect there.  So the patch is for that branch.

The fails I observed are:

FAIL: libgomp.oacc-c/../libgomp.oacc-c-c++-common/if-1.c 
-DACC_DEVICE_TYPE_nvidia=1 -DACC_MEM_SHARED=0 -foffload=nvptx-none execution test
FAIL: libgomp.oacc-c/../libgomp.oacc-c-c++-common/gang-static-2.c 
-DACC_DEVICE_TYPE_nvidia=1 -DACC_MEM_SHARED=0 -foffload=nvptx-none  -O0 
execution test
FAIL: libgomp.oacc-c/../libgomp.oacc-c-c++-common/gang-static-2.c 
-DACC_DEVICE_TYPE_nvidia=1 -DACC_MEM_SHARED=0 -foffload=nvptx-none  -O2 
execution test
FAIL: libgomp.oacc-c++/../libgomp.oacc-c-c++-common/if-1.c 
-DACC_DEVICE_TYPE_nvidia=1 -DACC_MEM_SHARED=0 -foffload=nvptx-none execution test
FAIL: libgomp.oacc-c++/../libgomp.oacc-c-c++-common/gang-static-2.c 
-DACC_DEVICE_TYPE_nvidia=1 -DACC_MEM_SHARED=0 -foffload=nvptx-none  -O0 
execution test
FAIL: libgomp.oacc-c++/../libgomp.oacc-c-c++-common/gang-static-2.c 
-DACC_DEVICE_TYPE_nvidia=1 -DACC_MEM_SHARED=0 -foffload=nvptx-none  -O2 
execution test


the diff I have is attached -- as you can see it's 'experimental'.

nathan

Index: builtins.c
===================================================================
--- builtins.c	(revision 228094)
+++ builtins.c	(working copy)
@@ -5866,6 +5866,8 @@ expand_stack_save (void)
 static rtx
 expand_builtin_acc_on_device (tree exp, rtx target)
 {
+   gcc_unreachable ();
+  
 #ifndef ACCEL_COMPILER
   gcc_assert (!get_oacc_fn_attrib (current_function_decl));
 #endif
@@ -10272,6 +10274,27 @@ fold_builtin_1 (location_t loc, tree fnd
 	return build_empty_stmt (loc);
       break;
 
+    case BUILT_IN_ACC_ON_DEVICE:
+      /* Don't fold on_device until we know which compiler is active.  */
+      if (symtab->state == EXPANSION)
+	{
+	  unsigned val_host = GOMP_DEVICE_HOST;
+	  unsigned val_dev = GOMP_DEVICE_NONE;
+
+#ifdef ACCEL_COMPILER
+	  val_host = GOMP_DEVICE_NOT_HOST;
+	  val_dev = ACCEL_COMPILER_acc_device;
+#endif
+	  tree host = build2 (EQ_EXPR, boolean_type_node, arg0,
+			      build_int_cst (integer_type_node, val_host));
+	  tree dev = build2 (EQ_EXPR, boolean_type_node, arg0,
+			     build_int_cst (integer_type_node, val_dev));
+
+	  tree result = build2 (TRUTH_OR_EXPR, boolean_type_node, host, dev);
+	  return fold_convert (integer_type_node, result);
+	}
+      break;
+
     default:
       break;
     }
Index: omp-low.c
===================================================================
--- omp-low.c	(revision 228094)
+++ omp-low.c	(working copy)
@@ -14725,21 +14725,20 @@ static void
 oacc_xform_on_device (gcall *call)
 {
   tree arg = gimple_call_arg (call, 0);
-  unsigned val = GOMP_DEVICE_HOST;
-	      
-#ifdef ACCEL_COMPILER
-  val = GOMP_DEVICE_NOT_HOST;
-#endif
-  tree result = build2 (EQ_EXPR, boolean_type_node, arg,
-			build_int_cst (integer_type_node, val));
+  unsigned val_host = GOMP_DEVICE_HOST;
+  unsigned val_dev = GOMP_DEVICE_NONE;
+
 #ifdef ACCEL_COMPILER
-  {
-    tree dev  = build2 (EQ_EXPR, boolean_type_node, arg,
-			build_int_cst (integer_type_node,
-				       ACCEL_COMPILER_acc_device));
-    result = build2 (TRUTH_OR_EXPR, boolean_type_node, result, dev);
-  }
+  val_host = GOMP_DEVICE_NOT_HOST;
+  val_dev = ACCEL_COMPILER_acc_device;
 #endif
+
+  tree host = build2 (EQ_EXPR, boolean_type_node, arg,
+		      build_int_cst (integer_type_node, val_host));
+  tree dev = build2 (EQ_EXPR, boolean_type_node, arg,
+		     build_int_cst (integer_type_node, val_dev));
+
+  tree result = build2 (TRUTH_OR_EXPR, boolean_type_node, host, dev);
   result = fold_convert (integer_type_node, result);
   tree lhs = gimple_call_lhs (call);
   gimple_seq seq = NULL;
@@ -14879,7 +14878,7 @@ execute_oacc_transform ()
 
 	gcall *call = as_a <gcall *> (stmt);
 	
-	if (gimple_call_builtin_p (call, BUILT_IN_ACC_ON_DEVICE))
+	if (0 && gimple_call_builtin_p (call, BUILT_IN_ACC_ON_DEVICE))
 	  /* acc_on_device must be evaluated at compile time for
 	     constant arguments.  */
 	  {