Reland #2 - [Offload] Introduce offload-tblgen and initial new API im…

…plementation (llvm#108413. llvm#117704) (llvm#117894)

Relands llvm#117704, which relanded changes from llvm#108413 - this was reverted
due to build issues. The new offload library did not build with
`LIBOMPTARGET_OMPT_SUPPORT` enabled, which was not picked up by
pre-merge testing.

The last commit contains the fix; everything else is otherwise identical
to the approved PR.
___

### New API

Previous discussions at the LLVM/Offload meeting have brought up the
need for a new API for exposing the functionality of the plugins. This
change introduces a very small subset of a new API, which is primarily
for testing the offload tooling and demonstrating how a new API can fit
into the existing code base without being too disruptive. Exact designs
for these entry points and future additions can be worked out over time.

The new API does however introduce the bare minimum functionality to
implement device discovery for Unified Runtime and SYCL. This means that
the `urinfo` and `sycl-ls` tools can be used on top of Offload. A
(rough) implementation of a Unified Runtime adapter (aka plugin) for
Offload is available
[here](https://github.com/callumfare/unified-runtime/tree/offload_adapter).
Our intention is to maintain this and use it to implement and test
Offload API changes with SYCL.

### Demoing the new API

```sh
# From the runtime build directory
$ ninja LibomptUnitTests
$ OFFLOAD_TRACE=1 ./offload/unittests/OffloadAPI/offload.unittests 
```


### Open questions and future work
* Only some of the available device info is exposed, and not all the
possible device queries needed for SYCL are implemented by the plugins.
A sensible next step would be to refactor and extend the existing device
info queries in the plugins. The existing info queries are all strings,
but the new API introduces the ability to return any arbitrary type.
* It may be sensible at some point for the plugins to implement the new
API directly, and the higher level code on top of it could be made
generic, but this is more of a long-term possibility.

offload/CMakeLists.txt

@@ -353,6 +353,9 @@ add_subdirectory(tools)
 # Build target agnostic offloading library.
 add_subdirectory(src)
 
+add_subdirectory(tools/offload-tblgen)
+add_subdirectory(liboffload)
+
 # Add tests.
 add_subdirectory(test)
 

offload/cmake/OpenMPTesting.cmake

@@ -48,6 +48,17 @@ function(find_standalone_test_dependencies)
     return()
   endif()
 
+  find_program(OFFLOAD_TBLGEN_EXECUTABLE
+    NAMES offload-tblgen
+    PATHS ${OPENMP_LLVM_TOOLS_DIR})
+  if (NOT OFFLOAD_TBLGEN_EXECUTABLE)
+    message(STATUS "Cannot find 'offload-tblgen'.")
+    message(STATUS "Please put 'not' in your PATH, set OFFLOAD_TBLGEN_EXECUTABLE to its full path, or point OPENMP_LLVM_TOOLS_DIR to its directory.")
+    message(WARNING "The check targets will not be available!")
+    set(ENABLE_CHECK_TARGETS FALSE PARENT_SCOPE)
+    return()
+  endif()
+
   find_program(OPENMP_NOT_EXECUTABLE
     NAMES not
     PATHS ${OPENMP_LLVM_TOOLS_DIR})
@@ -82,6 +93,7 @@ else()
     set(OPENMP_FILECHECK_EXECUTABLE ${LLVM_RUNTIME_OUTPUT_INTDIR}/FileCheck)
   endif()
   set(OPENMP_NOT_EXECUTABLE ${LLVM_RUNTIME_OUTPUT_INTDIR}/not)
+  set(OFFLOAD_TBLGEN_EXECUTABLE ${LLVM_RUNTIME_OUTPUT_INTDIR}/offload-tblgen)
   set(OFFLOAD_DEVICE_INFO_EXECUTABLE ${LLVM_RUNTIME_OUTPUT_INTDIR}/llvm-offload-device-info)
 endif()
 

offload/liboffload/API/APIDefs.td

@@ -0,0 +1,212 @@
+//===-- APIDefs.td - Base definitions for Offload tablegen -*- tablegen -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains the class definitions used to implement the Offload API,
+// as well as helper functions used to help populate relevant records.
+// See offload/API/README.md for more detailed documentation.
+//
+//===----------------------------------------------------------------------===//
+
+// Prefix for API naming. This could be hard-coded in the future when a value
+// is agreed upon.
+defvar PREFIX = "OL";
+defvar prefix = !tolower(PREFIX);
+
+// Parameter flags
+defvar PARAM_IN = 0x1;
+defvar PARAM_OUT = 0x2;
+defvar PARAM_OPTIONAL = 0x4;
+defvar PARAM_IN_OPTIONAL = !or(PARAM_IN, PARAM_OPTIONAL);
+defvar PARAM_OUT_OPTIONAL = !or(PARAM_OUT, PARAM_OPTIONAL);
+
+// Does the type end with '_handle_t'?
+class IsHandleType<string Type> {
+  // size("_handle_t") == 9
+  bit ret = !if(!lt(!size(Type), 9), 0,
+                !ne(!find(Type, "_handle_t", !sub(!size(Type), 9)), -1));
+}
+
+// Does the type end with '*'?
+class IsPointerType<string Type> {
+  bit ret = !ne(!find(Type, "*", !sub(!size(Type), 1)), -1);
+}
+
+// Describes the valid range of a pointer parameter that reperesents an array
+class Range<string Begin, string End> {
+  string begin = Begin;
+  string end = End;
+}
+
+// Names the parameters that indicate the type and size of the data pointed to
+// by an opaque pointer parameter
+class TypeInfo<string TypeEnum, string TypeSize> {
+  string enum = TypeEnum;
+  string size = TypeSize;
+}
+
+class Param<string Type, string Name, string Desc, bits<3> Flags = 0> {
+  string type = Type;
+  string name = Name;
+  string desc = Desc;
+  bits<3> flags = Flags;
+  Range range = Range<"", "">;
+  TypeInfo type_info = TypeInfo<"", "">;
+  bit IsHandle = IsHandleType<type>.ret;
+  bit IsPointer = IsPointerType<type>.ret;
+}
+
+// A parameter whose range is described by other parameters in the function.
+class RangedParam<string Type, string Name, string Desc, bits<3> Flags, Range ParamRange> : Param<Type, Name, Desc, Flags> {
+  let range = ParamRange;
+}
+
+// A parameter (normally of type void*) which has its pointee type and size
+// described by other parameters in the function.
+class TypeTaggedParam<string Type, string Name, string Desc, bits<3> Flags, TypeInfo ParamTypeInfo> : Param<Type, Name, Desc, Flags> {
+  let type_info = ParamTypeInfo;
+}
+
+class Return<string Value, list<string> Conditions = []> {
+  string value = Value;
+  list<string> conditions = Conditions;
+}
+
+class ShouldCheckHandle<Param P> {
+  bit ret = !and(P.IsHandle, !eq(!and(PARAM_OPTIONAL, P.flags), 0));
+}
+
+class ShouldCheckPointer<Param P> {
+  bit ret = !and(P.IsPointer, !eq(!and(PARAM_OPTIONAL, P.flags), 0));
+}
+
+// For a list of returns that contains a specific return code, find and append
+// new conditions to that return
+class AppendConditionsToReturn<list<Return> Returns, string ReturnValue,
+                               list<string> Conditions> {
+  list<Return> ret =
+      !foreach(Ret, Returns,
+               !if(!eq(Ret.value, ReturnValue),
+                   Return<Ret.value, Ret.conditions#Conditions>, Ret));
+}
+
+// Add null handle checks to a function's return value descriptions
+class AddHandleChecksToReturns<list<Param> Params, list<Return> Returns> {
+  list<string> handle_params =
+      !foreach(P, Params, !if(ShouldCheckHandle<P>.ret, P.name, ""));
+  list<string> handle_params_filt =
+      !filter(param, handle_params, !ne(param, ""));
+  list<string> handle_param_conds =
+      !foreach(handle, handle_params_filt, "`NULL == "#handle#"`");
+
+  // Does the list of returns already contain ERROR_INVALID_NULL_HANDLE?
+  bit returns_has_inv_handle = !foldl(
+      0, Returns, HasErr, Ret,
+      !or(HasErr, !eq(Ret.value, PREFIX#"_ERRC_INVALID_NULL_HANDLE")));
+
+  list<Return> returns_out = !if(returns_has_inv_handle,
+        AppendConditionsToReturn<Returns, PREFIX # "_ERRC_INVALID_NULL_HANDLE", handle_param_conds>.ret,
+        !listconcat(Returns, [Return<PREFIX # "_ERRC_INVALID_NULL_HANDLE", handle_param_conds>])
+    );
+}
+
+// Add null pointer checks to a function's return value descriptions
+class AddPointerChecksToReturns<list<Param> Params, list<Return> Returns> {
+  list<string> ptr_params =
+      !foreach(P, Params, !if(ShouldCheckPointer<P>.ret, P.name, ""));
+  list<string> ptr_params_filt = !filter(param, ptr_params, !ne(param, ""));
+  list<string> ptr_param_conds =
+      !foreach(ptr, ptr_params_filt, "`NULL == "#ptr#"`");
+
+  // Does the list of returns already contain ERROR_INVALID_NULL_POINTER?
+  bit returns_has_inv_ptr = !foldl(
+      0, Returns, HasErr, Ret,
+      !or(HasErr, !eq(Ret.value, PREFIX#"_ERRC_INVALID_NULL_POINTER")));
+  list<Return> returns_out = !if(returns_has_inv_ptr,
+        AppendConditionsToReturn<Returns, PREFIX # "_ERRC_INVALID_NULL_POINTER", ptr_param_conds>.ret,
+        !listconcat(Returns, [Return<PREFIX # "_ERRC_INVALID_NULL_POINTER", ptr_param_conds>])
+    );
+}
+
+defvar DefaultReturns = [Return<PREFIX#"_RESULT_SUCCESS">,
+                         Return<PREFIX#"_ERRC_UNINITIALIZED">,
+                         Return<PREFIX#"_ERRC_DEVICE_LOST">];
+
+class APIObject {
+  string name;
+  string desc;
+}
+
+class Function : APIObject {
+  list<Param> params;
+  list<Return> returns;
+  list<string> details = [];
+  list<string> analogues = [];
+
+  list<Return> returns_with_def = !listconcat(DefaultReturns, returns);
+  list<Return> all_returns = AddPointerChecksToReturns<params,
+        AddHandleChecksToReturns<params, returns_with_def>.returns_out>.returns_out;
+}
+
+class Etor<string Name, string Desc> {
+  string name = Name;
+  string desc = Desc;
+  string tagged_type;
+}
+
+class TaggedEtor<string Name, string Type, string Desc> : Etor<Name, Desc> {
+  let tagged_type = Type;
+}
+
+class Enum : APIObject {
+  // This refers to whether the enumerator descriptions specify a return
+  // type for functions where this enum may be used as an output type. If set,
+  // all Etor values must be TaggedEtor records
+  bit is_typed = 0;
+
+  list<Etor> etors = [];
+}
+
+class StructMember<string Type, string Name, string Desc> {
+  string type = Type;
+  string name = Name;
+  string desc = Desc;
+}
+
+defvar DefaultPropStructMembers =
+    [StructMember<prefix#"_structure_type_t", "stype",
+                  "type of this structure">,
+     StructMember<"void*", "pNext", "pointer to extension-specific structure">];
+
+class StructHasInheritedMembers<string BaseClass> {
+  bit ret = !or(!eq(BaseClass, prefix#"_base_properties_t"),
+                !eq(BaseClass, prefix#"_base_desc_t"));
+}
+
+class Struct : APIObject {
+  string base_class = "";
+  list<StructMember> members;
+  list<StructMember> all_members =
+      !if(StructHasInheritedMembers<base_class>.ret,
+          DefaultPropStructMembers, [])#members;
+}
+
+class Typedef : APIObject { string value; }
+
+class FptrTypedef : APIObject {
+  list<Param> params;
+  list<Return> returns;
+}
+
+class Macro : APIObject {
+  string value;
+
+  string condition;
+  string alt_value;
+}
+
+class Handle : APIObject;

offload/liboffload/API/CMakeLists.txt

@@ -0,0 +1,25 @@
+# The OffloadGenerate target is used to regenerate the generated files in the
+# include directory. These files are checked in with the rest of the source,
+# therefore it is only needed when making changes to the API.
+
+find_program(CLANG_FORMAT clang-format PATHS ${LLVM_TOOLS_BINARY_DIR} NO_DEFAULT_PATH)
+if (CLANG_FORMAT)
+    set(LLVM_TARGET_DEFINITIONS ${CMAKE_CURRENT_SOURCE_DIR}/OffloadAPI.td)
+
+    tablegen(OFFLOAD OffloadAPI.h -gen-api)
+    tablegen(OFFLOAD OffloadEntryPoints.inc -gen-entry-points)
+    tablegen(OFFLOAD OffloadFuncs.inc -gen-func-names)
+    tablegen(OFFLOAD OffloadImplFuncDecls.inc -gen-impl-func-decls)
+    tablegen(OFFLOAD OffloadPrint.hpp -gen-print-header)
+
+    set(OFFLOAD_GENERATED_FILES ${TABLEGEN_OUTPUT})
+    add_public_tablegen_target(OffloadGenerate)
+    add_custom_command(TARGET OffloadGenerate POST_BUILD COMMAND ${CLANG_FORMAT}
+        -i ${OFFLOAD_GENERATED_FILES})
+    add_custom_command(TARGET OffloadGenerate POST_BUILD COMMAND ${CMAKE_COMMAND}
+        -E copy_if_different ${OFFLOAD_GENERATED_FILES} "${CMAKE_CURRENT_SOURCE_DIR}/../include/generated")
+else()
+    message(WARNING "clang-format was not found, so the OffloadGenerate target\
+        will not be available. Offload will still build, but you will not be\
+        able to make changes to the API.")
+endif()