Revise design for optional features and AOT

sycl/doc/design/DeviceConfigFile.md

@@ -28,7 +28,7 @@ for this target. This information is optional because we plan to implement an
 auto-detection mechanism that is able to infer the `aot-toolchain` from the
 target name for well known targets.
 - [Optional] `aot-toolchain-%option_name` information to be passed to the
-`aot-toolchain` command. This information is optional. For some targets, the 
+`aot-toolchain` command. This information is optional. For some targets, the
 auto-detection mechanism might be able to infer values for this. One example of this
 information would be `ocloc-device %device_id`.
 
@@ -41,12 +41,13 @@ different tools and compiler modules:
     - Compiler driver requires `aot-toolchain` and `ocloc-device` to trigger the
     compilation for the required targets.
     [https://github.com/intel/llvm/pull/6775/files]
-- `sycl-aspect-filter`:
-https://github.com/intel/llvm/blob/sycl/sycl/doc/design/OptionalDeviceFeatures.md#aspect-filter-tool
+- `sycl-post-link` (see the description in the
+  [OptionalDeviceFeatures](./OptionalDeviceFeatures.md#new-filtering-pass-in-the-post-link-tool)
+  design doc).
 
 Finally, overhead should be minimal. Particularly, users should not pay for what
 they do not use. This motivates our decision to embed the default Device
-Configuration File rather than releasing it as a separate file. 
+Configuration File rather than releasing it as a separate file.
 
 ## High-Level Design
 The default Device Configuration File is a `.td` file located in the compiler
@@ -68,10 +69,10 @@ to implement new TableGen backends. Also, the [Search
 Indexes](https://llvm.org/docs/TableGen/BackEnds.html#search-indexes) backend
 already does something very similar to what we seek. It generates a table that
 provides a lookup function, but it cannot be extended with new entries. We can
-use _Search Indexes_ backend as inspiration for ours. 
+use _Search Indexes_ backend as inspiration for ours.
 
 Our backend should generate a map where the key is the target name and the value
-is an object of a custom class/struct including all the information required. 
+is an object of a custom class/struct including all the information required.
 
 Firstly, we need to provide a file describing the `DynamicTable` class. An
 example for this is `SearchableTable.td`, which describes `GenericEnum`, and
@@ -135,8 +136,8 @@ class DynamicTable {
 This file should be included --either directly or indirectly-- in any other
 `.td` file that uses `DynamicTable` class.
 
-The default device configuration `.td` file should look like the one below: 
-``` 
+The default device configuration `.td` file should look like the one below:
+```
 include "llvm/TableGen/DynamicTable.td"
 
 // Aspect and all the aspects definitions could be outlined
@@ -182,8 +183,8 @@ def AspectExt_intel_device_id : Aspect<"ext_intel_device_id">;
 def AspectExt_intel_memory_clock_rate : Aspect<"ext_intel_memory_clock_rate">;
 def AspectExt_intel_memory_bus_width : Aspect<"ext_intel_memory_bus_width">;
 def AspectEmulated : Aspect<"emulated">;
-    
-def TargetTable : DynamicTable { 
+
+def TargetTable : DynamicTable {
     let FilterClass = "TargetInfo";
     let Fields = ["TargetName", "aspects", "maySupportOtherAspects",
                   "subGroupSizes", "aotToolchain", "aotToolchainOptions"];
@@ -201,19 +202,19 @@ class TargetInfo <string tgtName, list<Aspect> aspectList, bit otherAspects,
     string aotToolchainOptions = options;
 }
 
-def : TargetInfo<"TargetA", [AspectCpu, AspectAtomic64], 
-                                  0, [8, 16], "ocloc", "-device tgtA">; 
+def : TargetInfo<"TargetA", [AspectCpu, AspectAtomic64],
+                                  0, [8, 16], "ocloc", "-device tgtA">;
 def : TargetInfo<"TargetB", [AspectGpu, AspectFp16],
                                   0, [8, 16], "ocloc", "-device tgtB">;
 def : TargetInfo<"TargetC", [AspectEmulated, AspectImage],
                                    0, [8, 32], "ocloc", "-device tgtC, -option2 val">;
 ```
-Note: backends tested don't allow lists within `TargetInfo` class. This is a 
+Note: backends tested don't allow lists within `TargetInfo` class. This is a
 backend limitation, rather than a TableGen limitation. Thus, we should be able
 to lift this limitation in our own backend, as shown in the initial prototype
 implemented to drive the design.
 
-The generated `.inc` file should look like the example below: 
+The generated `.inc` file should look like the example below:
 ```c++
 std::map<std::string, TargetInfo> TargetTable = {
     {"TargetA",
@@ -228,7 +229,7 @@ We also need a header file that includes the `.inc` file generated by the
 TableGen backend. Other backends don't generate the definition of `struct
 TargetInfo`, and this seems a good idea to me: it simplifies the backend
 implementation, and it is easier for developers to check the data structure
-to understand how to work with it. The idea is simply to define the struct 
+to understand how to work with it. The idea is simply to define the struct
 in this header file. This header file should look like the code below:
 ```c++
 namespace DeviceConfigFile {
@@ -247,7 +248,7 @@ using TargetTable_t = std::map<std::string, TargetInfo>;
 
 Other modules can query the map to get the information like in the example
 below:
-```c++ 
+```c++
 DeviceConfigFile::TargetInfo info = DeviceConfigFile::targets.find("TargetA");
 if (info == DeviceConfigFile::targets.end()) {
   /* Target not found */
@@ -262,7 +263,7 @@ if (info == DeviceConfigFile::targets.end()) {
 
 ## Tools and Modules Interacting with Device Config File
 This is a list of the tools and compiler modules that require using the file:
-- The *compiler driver* needs the file to determine the set of legal values for 
+- The *compiler driver* needs the file to determine the set of legal values for
 `-fsycl-targets`.
 - The *compiler driver* needs the file to define macros for `any_device_has/all_devices_have`.
 - *Clang* needs the file to emit diagnostics related to `-fsycl-fixed-targets.`
@@ -299,8 +300,8 @@ map with the new information about targets. LLVM provides
 [YAML/IO](https://llvm.org/docs/YamlIO.html) library to easily parse `.yaml`
 files. The driver should propagate this option to all the tools that require
 the Device Configuration File (e.g. `sycl-post-link`) so that each of the
-tools can modify the map according to the user extensions described in the 
-`.yaml` file. 
+tools can modify the map according to the user extensions described in the
+`.yaml` file.
 
 As mentioned in [Requirements](#requirements), there is an auto-detection
 mechanism for `aot-toolchain` and `aot-toolchain-options` that is able to
@@ -317,13 +318,13 @@ the other hand, it simply processes each new entry and updates the map with the
 latest information found.
 
 The auto-detection mechanism is a best effort to relieve users from specifying
-`aot-toolchain` and `aot-toolchain-options` from well known devices. However, 
+`aot-toolchain` and `aot-toolchain-options` from well known devices. However,
 it has its own limitations and potential issues:
 - Rules for target names: As of now, auto-detection is only available for Intel GPU
 targets. All targets starting with `intel_gpu_` will automatically set
 `aot-toolchain=ocloc` and `aot-toolchain-options=-device suffix` being suffix the part
 left after `intel_gpu_` prefix.
-- User specifies `aot-toolchain` and `aot-toolchain-options` for a target name 
+- User specifies `aot-toolchain` and `aot-toolchain-options` for a target name
 that can be auto-detected: user-specified information has precedence over auto-detected
 information.
 
@@ -341,7 +342,7 @@ via `device::has` for each device listed in the `.td` file. Both lists should ma
 This test could copy the mechanism of the test for `any_device_has` that goes over each
 item in `aspects.def` and tries to instantiate `any_device_has` with that enumerator.
 
-Neither of the tests provides guarantees that nothing went out-of-sync *per se*, we 
+Neither of the tests provides guarantees that nothing went out-of-sync *per se*, we
 would require running the second test in all the targets described in the `.td` file
 for such guarantees, but at least provides the mechanism to detect potential desyncs.