[Ada] Implement initialization of CUDA runtime

gcc/ada/

	* debug.adb: Document -gnatd_c flag as being used for CUDA.
	* gnat_cuda.ads: New file.
	* gnat_cuda.adb: New file.
	* rtsfind.ads: Add Interfaces_C_Strings package and
	RE_Fatbin_Wrapper, RE_Register_Fat_Binary,
	RE_Register_Fat_Binary_End, RE_Register_Function, RE_Chars_Ptr,
	RE_New_Char_Array entities.
	* rtsfind.adb: Create new Interfaces_C_Descendant subtype,
	handle it.
	* sem_ch7.adb (Analyze_Package_Body_Helper): Call CUDA init
	procedure.
	* sem_prag.adb (Analyze_Pragma): Call Add_Cuda_Kernel procedure.
	* gcc-interface/Make-lang.in (GNAT_ADA_OBJS): Add gnat_cuda.o.

1 files changed, 107 insertions, 0 deletions

diff --git a/gcc/ada/gnat_cuda.ads b/gcc/ada/gnat_cuda.ads
new file mode 100644
index 0000000..e27be34
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+++ b/gcc/ada/gnat_cuda.ads
@@ -0,0 +1,107 @@
+------------------------------------------------------------------------------
+--                                                                          --
+--                         GNAT COMPILER COMPONENTS                         --
+--                                                                          --
+--                                 C U D A                                  --
+--                                                                          --
+--                                 S p e c                                  --
+--                                                                          --
+--          Copyright (C) 2010-2020, Free Software Foundation, Inc.         --
+--                                                                          --
+-- GNAT is free software;  you can  redistribute it  and/or modify it under --
+-- terms of the  GNU General Public License as published  by the Free Soft- --
+-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
+-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
+-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
+-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
+-- for  more details.  You should have  received  a copy of the GNU General --
+-- Public License  distributed with GNAT; see file COPYING3.  If not, go to --
+-- http://www.gnu.org/licenses for a complete copy of the license.          --
+--                                                                          --
+-- GNAT was originally developed  by the GNAT team at  New York University. --
+-- Extensive contributions were provided by Ada Core Technologies Inc.      --
+--                                                                          --
+------------------------------------------------------------------------------
+
+--  This package defines CUDA-specific datastructures and subprograms.
+--
+--  Compiling for CUDA requires compiling for two targets. One is the CPU (more
+--  frequently named "host"), the other is the GPU (the "device"). Compiling
+--  for the host requires compiling the whole program. Compiling for the device
+--  only requires compiling packages that contain CUDA kernels.
+--
+--  When compiling for the device, GNAT-LLVM is used. It produces assembly
+--  tailored to Nvidia's GPU (NVPTX). This NVPTX code is then assembled into
+--  an object file by ptxas, an assembler provided by Nvidia. This object file
+--  is then combined with its source code into a fat binary by a tool named
+--  `fatbin`, also provided by Nvidia. The resulting fat binary is turned into
+--  a regular object file by the host's linker and linked with the program that
+--  executes on the host.
+--
+--  A CUDA kernel is a procedure marked with the CUDA_Global pragma or aspect.
+--  CUDA_Global does not have any effect when compiling for the device. When
+--  compiling for the host, the frontend stores procedures marked with
+--  CUDA_Global in a hash table the key of which is the Node_Id of the package
+--  body that contains the CUDA_Global procedure. This is done in sem_prag.adb.
+--  Once the declarations of a package body have been analyzed, variable, type
+--  and procedure declarations necessary for the initialization of the CUDA
+--  runtime are appended to the package that contains the CUDA_Global
+--  procedure.
+--
+--  These declarations are used to register the CUDA kernel with the CUDA
+--  runtime when the program is launched. Registering a CUDA kernel with the
+--  CUDA runtime requires multiple function calls:
+--  - The first one registers the fat binary which corresponds to the package
+--    with the CUDA runtime.
+--  - Then, as many function calls as there are kernels in order to bind them
+--    with the fat binary.
+--    fat binary.
+--  - The last call lets the CUDA runtime know that we are done initializing
+--    CUDA.
+--  Expansion of the CUDA_Global aspect is triggered in sem_ch7.adb, during
+--  analysis of the package. All of this expansion is performed in the
+--  Insert_CUDA_Initialization procedure defined in GNAT_CUDA.
+--
+--  Once a CUDA package is initialized, its kernels are ready to be used.
+--  Launching CUDA kernels is done by using the CUDA_Execute pragma. When
+--  compiling for the host, the CUDA_Execute pragma is expanded into a declare
+--  block which performs calls to the CUDA runtime functions.
+--  - The first one pushes a "launch configuration" on the "configuration
+--    stack" of the CUDA runtime.
+--  - The second call pops this call configuration, making it effective.
+--  - The third call actually launches the kernel.
+--  Light validation of the CUDA_Execute pragma is performed in sem_prag.adb
+--  and expansion is performed in exp_prag.adb.
+
+with Types; use Types;
+
+package GNAT_CUDA is
+
+   procedure Add_CUDA_Kernel (Pack_Id : Entity_Id; Kernel : Entity_Id);
+   --  Add Kernel to the list of CUDA_Global nodes that belong to Pack_Id.
+   --  Kernel is a procedure entity marked with CUDA_Global, Pack_Id is the
+   --  entity of its parent package body.
+
+   procedure Build_And_Insert_CUDA_Initialization (N : Node_Id);
+   --  Builds declarations necessary for CUDA initialization and inserts them
+   --  in N, the package body that contains CUDA_Global nodes. These
+   --  declarations are:
+   --
+   --    * A symbol to hold the pointer to the CUDA fat binary
+   --
+   --    * A type definition for a wrapper that contains the pointer to the
+   --      CUDA fat binary
+   --
+   --    * An object of the aforementioned type to hold the aforementioned
+   --      pointer.
+   --
+   --    * For each CUDA_Global procedure in the package, a declaration of a C
+   --      string containing the function's name.
+   --
+   --    * A function that takes care of calling CUDA functions that register
+   --      CUDA_Global procedures with the runtime.
+   --
+   --    * A boolean that holds the result of the call to the aforementioned
+   --      function.
+
+end GNAT_CUDA;