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* [Patch] nvptx: Add -mptx=6.0 + -misa=sm_70
@ 2022-02-17 17:24 Tobias Burnus
  2022-02-22 14:26 ` Tom de Vries
                   ` (2 more replies)
  0 siblings, 3 replies; 14+ messages in thread
From: Tobias Burnus @ 2022-02-17 17:24 UTC (permalink / raw)
  To: Tom de Vries, gcc-patches

[-- Attachment #1: Type: text/plain, Size: 4161 bytes --]

This patch exposes two -m* option values which are already
internally available. I think it makes sense to expose them
explicitly to the user (see below), but there are also arguments
against. Thoughts?


PTX version (-mptx=)
[patch adds -mptx=6.0 as option]

* Currently supported internally are 3.1 (CUDA 5.0, used by GCC <= 11),
   6.0 (CUDA 9.0, current GCC 12 default), 6.3 (CUDA 10.0), 7.0 (CUDA 11.0)
* -mptx= supports 3.1, 6.3, 7.0 – but not the internal default 6.0

First, I think all versions make sense:
* 3.1 is the previous default and permits running with older CUDA (if need)
* 6.0 is for CUDA 9 - and if we want to support it, it has to stay.
   6.0 is the default since commit
   https://gcc.gnu.org/pipermail/gcc-patches/2022-February/590007.html
* 6.3 is CUDA 10.0. In that PTX version, a lot of nice features
   were added like .alias
* 7.0 is CUDA 11.0. This adds support for sm_80 (honored in code gen).

PTX >= 6.0 makes sense as it permits newer sm_* (in particular: sm_53 and sm_70)
and
+  /* Pick at least 6.0, to enable using bar.warp.sync to have a way to force
+     warp convergence.  */
On the other hand, for older systems, CUDA 10.0 might be too new and we still
want to support CUDA 9. (At least that's how I understood one of nvpx gcc
emails, which I cannot find at the moment.)

Assuming we don't want to change the default minimal version from PTX 6.0
back to 6.3, it looks as both should stay.
Downside: we probably need one lib{c,gomp,gfortran,...} per PTX version,
i.e. 4 versions (3.1, 6.0, 6.3, 7.0).

I think it makes sense to expose the 6.0 value to the user and not
only use it internally behind the scenes. As it is already used internally,
the change is tiny but user visible. Thus, it has to stay when we will
bump the default in later GCC versions; on the other hand, if we bump
the default, it might be also a good reason to have it to permit the
user to have a backward compatible PTX output for linking libraries.

  * * *

SM version (-misa=)
[Patch adds -misa=sm_70]

* The compiler supports internally: SM_30, SM_35, SM_53, SM_70, SM_75, SM_80.
* GCC <= 11 only had sm_30 and sm_35 (supported since PTX 3.1/CUDA 5.0)
* GCC 12 exposes
   - sm_30, sm_35,
   - sm_53 (PTX 4.2, CUDA 7.0),
   - sm_75 (PTX 6.3, CUDA 10.0)
   - sm_80 (PTX 7.0, CUDA 11.0)
   but it does not permit using -misa=sm_70 (PTX 6.0, CUDA 9.0).
* Note: sm_75 + sm_80 imply a newer PTX version, which
   the compiler defaults to (if no -mptx= has been specified).

I think it makes sense to have sm_70 in addition:
* sm_70 enables several new features (see PTX documentation)
* sm_70 is the highest supported for CUDA 9 (default PTX version);
   as sm_75 will require CUDA 10, currently only sm_53 can be used with CUDA 9.
* The current code actually does generate different code for >= sm_70
   already.

  * * *

This patch updates -misa= and -mptx= documentation to match what actually has
been implemented. I think that makes sense as:
* The currently documented default for -mptx= is no longer true.
* The available values are already exposed via the diagnostic
* The multilib issue already occurs when the user explicitly specifies -mptx=6.3
   (or -mptx=3.1).
* If needed, we could note that certain PTX or ISA values are experimental.

I think besides > sm_35 being experimental, there is no reason that higher sm_*
should not be used. Except for the pre-existing multilib issue and for the ICE
when bootstrapping with sm_53 (instead of sm_35) as default ISA version.
But that's solved by Roger's patch (pending ME (and then BE) review),
https://gcc.gnu.org/pipermail/gcc-patches/2022-February/590545.html

* * *

Comments to any of those three patches (-mptx=6.0, -misa=sm_70, documentation)?
(Lightly tested on x86-64 with nvptx offloading.)
OK? (All, some?)

Tobias
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nvptx: Add -mptx=6.0 + -misa=sm_70

gcc/ChangeLog:

	* config/nvptx/nvptx-c.cc (nvptx_cpu_cpp_builtins): Handle SM70.
	* gcc/config/nvptx/nvptx.cc (first_ptx_version_supporting_sm):
	Likewise.
	* config/nvptx/nvptx.opt (misa): Add sm_70 alias PTX_ISA_SM70.
	(mptx): Add 6.0 alias PTX_VERSION_6_0.
	* config/nvptx/t-omp-device: Add sm_53, sm_70, sm_75, sm_80.
	* doc/invoke.texi (-misa, -mptx): Update for new values and
	defaults.

 gcc/config/nvptx/nvptx-c.cc   |  2 ++
 gcc/config/nvptx/nvptx.cc     |  2 ++
 gcc/config/nvptx/nvptx.opt    |  6 ++++++
 gcc/config/nvptx/t-omp-device |  2 +-
 gcc/doc/invoke.texi           | 17 +++++++++++------
 5 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/gcc/config/nvptx/nvptx-c.cc b/gcc/config/nvptx/nvptx-c.cc
index d68b9910d7e..b2375fb5b16 100644
--- a/gcc/config/nvptx/nvptx-c.cc
+++ b/gcc/config/nvptx/nvptx-c.cc
@@ -43,6 +43,8 @@ nvptx_cpu_cpp_builtins (void)
     cpp_define (parse_in, "__PTX_SM__=800");
   else if (TARGET_SM75)
     cpp_define (parse_in, "__PTX_SM__=750");
+  else if (TARGET_SM70)
+    cpp_define (parse_in, "__PTX_SM__=700");
   else if (TARGET_SM53)
     cpp_define (parse_in, "__PTX_SM__=530");
   else if (TARGET_SM35)
diff --git a/gcc/config/nvptx/nvptx.cc b/gcc/config/nvptx/nvptx.cc
index afbad5bdde6..f3f3201a7ba 100644
--- a/gcc/config/nvptx/nvptx.cc
+++ b/gcc/config/nvptx/nvptx.cc
@@ -217,6 +217,8 @@ first_ptx_version_supporting_sm (enum ptx_isa sm)
       return PTX_VERSION_3_1;
     case PTX_ISA_SM53:
       return PTX_VERSION_4_2;
+    case PTX_ISA_SM70:
+      return PTX_VERSION_6_0;
     case PTX_ISA_SM75:
       return PTX_VERSION_6_3;
     case PTX_ISA_SM80:
diff --git a/gcc/config/nvptx/nvptx.opt b/gcc/config/nvptx/nvptx.opt
index e3f65b2d0b1..c00af111829 100644
--- a/gcc/config/nvptx/nvptx.opt
+++ b/gcc/config/nvptx/nvptx.opt
@@ -64,6 +64,9 @@ Enum(ptx_isa) String(sm_35) Value(PTX_ISA_SM35)
 EnumValue
 Enum(ptx_isa) String(sm_53) Value(PTX_ISA_SM53)
 
+EnumValue
+Enum(ptx_isa) String(sm_70) Value(PTX_ISA_SM70)
+
 EnumValue
 Enum(ptx_isa) String(sm_75) Value(PTX_ISA_SM75)
 
@@ -82,6 +85,9 @@ Known PTX versions (for use with the -mptx= option):
 EnumValue
 Enum(ptx_version) String(3.1) Value(PTX_VERSION_3_1)
 
+EnumValue
+Enum(ptx_version) String(6.0) Value(PTX_VERSION_6_0)
+
 EnumValue
 Enum(ptx_version) String(6.3) Value(PTX_VERSION_6_3)
 
diff --git a/gcc/config/nvptx/t-omp-device b/gcc/config/nvptx/t-omp-device
index 8765d9f1881..4228218a424 100644
--- a/gcc/config/nvptx/t-omp-device
+++ b/gcc/config/nvptx/t-omp-device
@@ -1,4 +1,4 @@
 omp-device-properties-nvptx: $(srcdir)/config/nvptx/nvptx.cc
 	echo kind: gpu > $@
 	echo arch: nvptx >> $@
-	echo isa: sm_30 sm_35 >> $@
+	echo isa: sm_30 sm_35 sm_53 sm_70 sm_75 sm_80 >> $@
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index e1a00c80307..54ca0070356 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -27250,15 +27250,20 @@ supported.
 
 @item -misa=@var{ISA-string}
 @opindex march
-Generate code for given the specified PTX ISA (e.g.@: @samp{sm_35}).  ISA
-strings must be lower-case.  Valid ISA strings include @samp{sm_30} and
-@samp{sm_35}.  The default ISA is sm_35.
+Generate code for given the specified PTX ISA (e.g.@: @samp{sm_70}).  ISA
+strings must be lower-case.  Valid ISA strings include @samp{sm_30},
+@samp{sm_35}, @samp{sm_53}, @samp{sm_70}, @samp{sm_75}, and @samp{sm_80}.
+The default ISA is sm_35.
 
 @item -mptx=@var{version-string}
 @opindex mptx
-Generate code for given the specified PTX version (e.g.@: @samp{6.3}).
-Valid version strings include @samp{3.1} and @samp{6.3}.  The default PTX
-version is 3.1.
+Generate code for given the specified PTX version (e.g.@: @samp{7.0}).
+Valid version strings include @samp{3.1}, @samp{6.0}, @samp{6.3}, and
+@samp{7.0}.  The default PTX version is 6.0, unless a higher minimal
+version is required for specified PTX ISA via option @option{-misa=}.
+
+the lowest supported
+PTX version supporting
 
 @item -mmainkernel
 @opindex mmainkernel

^ permalink raw reply	[flat|nested] 14+ messages in thread
end of thread, other threads:[~2023-11-30 14:59 UTC | newest]

Thread overview: 14+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-02-17 17:24 [Patch] nvptx: Add -mptx=6.0 + -misa=sm_70 Tobias Burnus
2022-02-22 14:26 ` Tom de Vries
2022-02-22 14:39 ` Tom de Vries
2022-02-22 14:43 ` Tom de Vries
2022-02-22 16:03   ` Tobias Burnus
2022-02-24  8:29     ` Tom de Vries
2022-02-24 10:01       ` [PATCH][libgomp, testsuite, nvptx] Add libgomp.c/declare-variant-3-sm*.c Tom de Vries
2022-02-24 10:09         ` Jakub Jelinek
2022-02-24 10:32           ` Tom de Vries
2022-02-24 10:38             ` Jakub Jelinek
2023-11-30 14:48             ` Fix 'libgomp.c/declare-variant-3-*.c' compilation for configurations where GCN offloading is enabled in addition to nvptx (was: [PATCH][libgomp, testsuite, nvptx] Add libgomp.c/declare-variant-3-sm*.c) Thomas Schwinge
2023-11-30 14:49               ` Thomas Schwinge
2023-11-30 14:57             ` In 'libgomp.c/declare-variant-{3,4}-*.c', restrict 'scan-offload-tree-dump's to 'only_for_offload_target [...]' " Thomas Schwinge
2023-11-30 14:59             ` Spin 'dg-do run' part of 'libgomp.c/declare-variant-3-sm30.c' off into new 'libgomp.c/declare-variant-3.c' " Thomas Schwinge

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