[PATCH] D60763: Prototype OpenCL BIFs using Tablegen

Pierre via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Tue Apr 16 01:45:13 PDT 2019

Pierre created this revision.
Pierre added reviewers: Anastasia, svenvh.
Herald added subscribers: cfe-commits, yaxunl, mgorny.
Herald added a project: clang.

**This is a re-upload of the patch from Joey GOULY, posted at: https://reviews.llvm.org/D53023 . I am re-uploading it because I will continue his work on this, and it is better if I have control on the post on phabricator.**
This patch contains a prototype to generate OpenCL builtin functions with Tablegen. Not all builtin functions have been implemented. This prototype is intented to replace the use of the opencl-c.h file currently included in all OpenCL programs. To recall, this file contains contains all the overloaded builtin functions. Using clang-tblgen would allow to factorize all these function declarations and include them only if they are called.

**A copy-paste from the original description:**

This is the prototype for the approach that was mentioned by Anastasia in http://lists.llvm.org/pipermail/cfe-dev/2018-September/059529.html

The tablegen file describes the BIFs and all their overloads, in hopefully a concise manner.

There are 3 things generated from the OpenCLBuiltins.td file.

1. OpenCLArgTypes[], this is a table containing all the different types of overloads. This is a separate table so it can be shared by the BIFs.
2. OpenCLBuiltins[], this is a table that contains all the overloads for the BIFs.
3. isOpenCLBuiltin, this is a function that uses a trie-like switch/case to determine if a StringRef is the name of a BIF.

Just a quick snippet of the above:

  OpenCLType OpenCLArgTypes[] = {
  // 0
  { OCLT_float, 0, 0, clang::LangAS::Default, },
  // 1
  { OCLT_float, 2, 0, clang::LangAS::Default, },

  OpenCLBuiltinDecl OpenCLBuiltins[] = {
  // acos
    { { OCLT_float, 0, 0, clang::LangAS::Default, }, 1, 0, "", 100,  },
    { { OCLT_float, 2, 0, clang::LangAS::Default, }, 1, 1, "", 100,  },

  std::pair<unsigned, unsigned> isOpenCLBuiltin(llvm::StringRef name) {
    switch (name.size()) {
    default: break;
    case 3:  // 1 string to match.
      if (memcmp(name.data()+0, "foo", 3) != 0)
      return std::make_pair(707, 2);   // "foo"

While it's a prototype, I have tried to keep it as clean as possible.


1. Bit-pack the tables to reduce the size.
2. Include the return type in the ArgTypes table to reduce the size.
3. Measure the performance / size impact
4. Auto-generate parts of OCL2Qual, to reduce repeated typing
5. OCL2Qual does not support pointers-to-pointers currently, but I believe no BIFs use that.
6. InsertBuiltinDeclarations builds up an AST function declaration manually, perhaps there is a helper function for this.
7. There is a FIXME in SemaDecl.cpp that needs to be implemented.

  rC Clang



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