[Patch] libgomp.texi: Reverse-offload updates (was: [Patch] libgomp: Handle OpenMP's reverse offloads)

[Tobias Burnus <tobias@codesourcery.com>]

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On 06.12.22 08:45, Tobias Burnus wrote:
> * As follow-up,  libgomp.texi must be updated

That is what the attached patch does – obviously, it is depending on the
main patch.

OK (once the main patch is in)?

Tobias
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libgomp.texi: Reverse-offload updates

libgomp/
	* libgomp.texi (5.0 Impl. Status): Update 'requires' and 'ancestor'.
	(GCN): Add item about 'omp requires'.
	(nvptx): Likewise; add item about reverse offload.

diff --git a/libgomp/libgomp.texi b/libgomp/libgomp.texi
index efa7d956a33..e9ab079ecf5 100644
--- a/libgomp/libgomp.texi
+++ b/libgomp/libgomp.texi
@@ -192,8 +192,8 @@ The OpenMP 4.5 specification is fully supported.
       env variable @tab Y @tab
 @item Nested-parallel changes to @emph{max-active-levels-var} ICV @tab Y @tab
 @item @code{requires} directive @tab P
-      @tab complete but no non-host devices provides @code{unified_address},
-      @code{unified_shared_memory} or @code{reverse_offload}
+      @tab complete but no non-host devices provides @code{unified_address} or
+      @code{unified_shared_memory}
 @item @code{teams} construct outside an enclosing target region @tab Y @tab
 @item Non-rectangular loop nests @tab Y @tab
 @item @code{!=} as relational-op in canonical loop form for C/C++ @tab Y @tab
@@ -228,7 +228,7 @@ The OpenMP 4.5 specification is fully supported.
 @item @code{allocate} clause @tab P @tab Initial support
 @item @code{use_device_addr} clause on @code{target data} @tab Y @tab
 @item @code{ancestor} modifier on @code{device} clause
-      @tab Y @tab See comment for @code{requires}
+      @tab Y @tab Host fallback with GCN devices
 @item Implicit declare target directive @tab Y @tab
 @item Discontiguous array section with @code{target update} construct
       @tab N @tab
@@ -288,7 +288,7 @@ The OpenMP 4.5 specification is fully supported.
       @code{append_args} @tab N @tab
 @item @code{dispatch} construct @tab N @tab
 @item device-specific ICV settings with environment variables @tab Y @tab
-@item @code{assume} directive @tab Y @tab
+@item @code{assume} and @code{assumes} directives @tab Y @tab
 @item @code{nothing} directive @tab Y @tab
 @item @code{error} directive @tab Y @tab
 @item @code{masked} construct @tab Y @tab
@@ -4455,6 +4455,9 @@ The implementation remark:
 @item I/O within OpenMP target regions and OpenACC parallel/kernels is supported
       using the C library @code{printf} functions and the Fortran
       @code{print}/@code{write} statements.
+@item OpenMP code that has a requires directive with @code{unified_address},
+      @code{unified_shared_memory} or @code{reverse_offload} will remove
+      any GCN device from the list of available devices (``host fallback'').
 @end itemize
 
 
@@ -4504,6 +4507,13 @@ The implementation remark:
 @item Compilation OpenMP code that contains @code{requires reverse_offload}
       requires at least @code{-march=sm_35}, compiling for @code{-march=sm_30}
       is not supported.
+@item For code containing reverse offload (i.e. @code{target} regions with
+      @code{device(ancestor:1)}), there is a slight performance penality
+      for @emph{all} target regions, consisting mostly of shutdown delay
+      between zero to one microsecond and a tiny device querying overhead.
+@item OpenMP code that has a requires directive with @code{unified_address}
+      or @code{unified_shared_memory} will remove any nvptx device from the
+      list of available devices (``host fallback'').
 @end itemize