Host and offload targets have no common meaning of address spaces

Message ID 877db4djc1.fsf@euler.schwinge.homeip.net
State New
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  • Host and offload targets have no common meaning of address spaces
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Commit Message

Thomas Schwinge Jan. 13, 2022, 10:24 a.m.
Hi!

Jakub, I'd still like your comment on the two "should we" questions cited
below.

On 2021-08-24T13:43:38+0200, Richard Biener via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
> On Tue, Aug 24, 2021 at 12:23 PM Thomas Schwinge <thomas@codesourcery.com> wrote:

>> On 2021-08-19T22:13:56+0200, I wrote:

>> > On 2021-08-16T10:21:04+0200, Jakub Jelinek <jakub@redhat.com> wrote:

>> >> On Mon, Aug 16, 2021 at 10:08:42AM +0200, Thomas Schwinge wrote:

>> > |> Concerning the current 'gcc/omp-low.c:omp_build_component_ref', for the

>> > |> current set of offloading testcases, we never see a

>> > |> '!ADDR_SPACE_GENERIC_P' there, so the address space handling doesn't seem

>> > |> to be necessary there (but also won't do any harm: no-op).

>> >>

>> >> Are you sure this can't trigger?

>> >> Say

>> >> extern int __seg_fs a;

>> >>

>> >> void

>> >> foo (void)

>> >> {

>> >>   #pragma omp parallel private (a)

>> >>   a = 2;

>> >> }

>> >

>> > That test case doesn't run into 'omp_build_component_ref' at all,

>> > but [I've pushed an altered and extended variant that does],

>> > "Add 'libgomp.c/address-space-1.c'".

>> >

>> > In this case, 'omp_build_component_ref' called via host compilation

>> > 'pass_lower_omp', it's the 'field_type' that has 'address-space-1'

>> > [...]:

>> >

>> >     (gdb) call debug_tree(field_type)

>> >      <pointer_type 0x7ffff7686b28

>> >         type <integer_type 0x7ffff7686498 int address-space-1 SI

>>

>> >> I think keeping the qual addr space here is the wrong thing to do,

>> >> it should keep the other quals and clear the address space instead,

>> >> the whole struct is going to be in generic addres space, isn't it?

>> >

>> > Correct for 'omp_build_component_ref' called via host compilation

>> > 'pass_lower_omp'

>>

>> > However, regarding the former comment -- shouldn't we force generic

>> > address space for all 'tree' types read in via LTO streaming for

>> > offloading compilation?  I assume that (in the general case) address

>> > spaces are never compatible between host and offloading compilation?

>> > For [...] "Add 'libgomp.c/address-space-1.c'", propagating the

>> > '__seg_fs' address space across the offloading boundary (assuming I did

>> > interpret the dumps correctly) doesn't seem to cause any problems

>>

>> As I found later, actually the 'address-space-1' per host '__seg_fs' does

>> cause the "Intel MIC (emulated) offloading execution failure"

>> mentioned/XFAILed for 'libgomp.c/address-space-1.c': SIGSEGV, like

>> (expected) for host execution.  For GCN offloading target, it maps to

>> GCN 'ADDR_SPACE_FLAT' which apparently doesn't cause any ill effects (for

>> that simple test case).  The nvptx offloading target doesn't consider

>> address spaces at all.

>>

>> Is the attached "Host and offload targets have no common meaning of

>> address spaces" OK to push?


> I'd

> say I agree that any host address-space should go away when the corresponding

> data is offloaded


Pushed to master branch commit 9fcc3a1dd2372deea8856c55d25337b06e201203
"Host and offload targets have no common meaning of address spaces", see
attached.


>> Then, is that the way to do this, or should we add in

>> 'gcc/tree-streamer-out.c:pack_ts_base_value_fields':

>>

>>     if (lto_stream_offload_p)

>>       gcc_assert (ADDR_SPACE_GENERIC_P (TYPE_ADDR_SPACE (expr)));

>>

>> ..., and elsewhere sanitize this for offloading compilation?  Jakub's

>> suggestion above, regarding 'gcc/omp-low.c:omp_build_component_ref':

>>

>> | I think keeping the qual addr space here is the wrong thing to do,

>> | it should keep the other quals and clear the address space instead

>>

>> But it's not obvious to me that indeed this is the one place where this

>> would need to be done?  (It ought to work for

>> 'libgomp.c/address-space-1.c', and any other occurrences would run into

>> the 'assert', so that ought to be "fine", though?)

>>

>>

>> And, should we have a new hook

>> 'void targetm.addr_space.validate (addr_space_t as)' (better name?),

>> called via 'gcc/emit-rtl.c:set_mem_attrs' (only? -- assuming this is the

>> appropriate canonic function where address space use is observed?), to

>> make sure that the requested 'as' is valid for the target?

>> 'default_addr_space_validate' would refuse everything but

>> 'ADDR_SPACE_GENERIC_P (as)'; this hook would need implementing for all

>> handful of targets making use of address spaces (supposedly matching the

>> logic how they call 'c_register_addr_space'?).  (The closest existing

>> hook seems to be 'targetm.addr_space.diagnose_usage', only defined for

>> AVR, and called from "the front ends" (C only).)



Grüße
 Thomas


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Patch

From 9fcc3a1dd2372deea8856c55d25337b06e201203 Mon Sep 17 00:00:00 2001
From: Thomas Schwinge <thomas@codesourcery.com>
Date: Tue, 24 Aug 2021 11:14:10 +0200
Subject: [PATCH] Host and offload targets have no common meaning of address
 spaces

	gcc/
	* tree-streamer-out.c (pack_ts_base_value_fields): Don't pack
	'TYPE_ADDR_SPACE' for offloading.
	* tree-streamer-in.c (unpack_ts_base_value_fields): Don't unpack
	'TYPE_ADDR_SPACE' for offloading.
	libgomp/
	* testsuite/libgomp.c/address-space-1.c: Remove 'dg-xfail-run-if'
	for 'offload_device_intel_mic'.
---
 gcc/tree-streamer-in.c                        | 2 ++
 gcc/tree-streamer-out.c                       | 7 ++++++-
 libgomp/testsuite/libgomp.c/address-space-1.c | 4 ----
 3 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/gcc/tree-streamer-in.c b/gcc/tree-streamer-in.c
index adaf624bda7..0d5108e36a0 100644
--- a/gcc/tree-streamer-in.c
+++ b/gcc/tree-streamer-in.c
@@ -146,7 +146,9 @@  unpack_ts_base_value_fields (struct bitpack_d *bp, tree expr)
 	TYPE_REVERSE_STORAGE_ORDER (expr) = (unsigned) bp_unpack_value (bp, 1);
       else
 	TYPE_SATURATING (expr) = (unsigned) bp_unpack_value (bp, 1);
+#ifndef ACCEL_COMPILER
       TYPE_ADDR_SPACE (expr) = (unsigned) bp_unpack_value (bp, 8);
+#endif
     }
   else if (TREE_CODE (expr) == BIT_FIELD_REF || TREE_CODE (expr) == MEM_REF)
     {
diff --git a/gcc/tree-streamer-out.c b/gcc/tree-streamer-out.c
index 8742bf09c6a..23d15a50670 100644
--- a/gcc/tree-streamer-out.c
+++ b/gcc/tree-streamer-out.c
@@ -119,7 +119,12 @@  pack_ts_base_value_fields (struct bitpack_d *bp, tree expr)
 	bp_pack_value (bp, TYPE_REVERSE_STORAGE_ORDER (expr), 1);
       else
 	bp_pack_value (bp, TYPE_SATURATING (expr), 1);
-      bp_pack_value (bp, TYPE_ADDR_SPACE (expr), 8);
+      if (lto_stream_offload_p)
+	/* Host and offload targets have no common meaning of address
+	   spaces.  */
+	;
+      else
+	bp_pack_value (bp, TYPE_ADDR_SPACE (expr), 8);
     }
   else if (TREE_CODE (expr) == BIT_FIELD_REF || TREE_CODE (expr) == MEM_REF)
     {
diff --git a/libgomp/testsuite/libgomp.c/address-space-1.c b/libgomp/testsuite/libgomp.c/address-space-1.c
index 6ad57deec42..39ff82c1429 100644
--- a/libgomp/testsuite/libgomp.c/address-space-1.c
+++ b/libgomp/testsuite/libgomp.c/address-space-1.c
@@ -3,10 +3,6 @@ 
 /* { dg-do run { target i?86-*-* x86_64-*-* } } */
 /* { dg-require-effective-target offload_device_nonshared_as } */
 
-/* With Intel MIC (emulated) offloading:
-       offload error: process on the device 0 unexpectedly exited with code 0
-   { dg-xfail-run-if TODO { offload_device_intel_mic } } */
-
 #include <assert.h>
 
 int __seg_fs a;
-- 
2.34.1