Emit !callback metadata and introduce the callback attribute

  With commit r351627, LLVM gained the ability to apply (existing) IPO
  optimizations on indirections through callbacks, or transitive calls.
  The general idea is that we use an abstraction to hide the middle man
  and represent the callback call in the context of the initial caller.
  It is described in more detail in the commit message of the LLVM patch
  r351627, the llvm::AbstractCallSite class description, and the
  language reference section on callback-metadata.

  This commit enables clang to emit !callback metadata that is
  understood by LLVM. It does so in three different cases:
    1) For known broker functions declarations that are directly
       generated, e.g., __kmpc_fork_call for the OpenMP pragma parallel.
    2) For known broker functions that are identified by their name and
       source location through the builtin detection, e.g.,
       pthread_create from the POSIX thread API.
    3) For user annotated functions that carry the "callback(callee, ...)"
       attribute. The attribute has to include the name, or index, of
       the callback callee and how the passed arguments can be
       identified (as many as the callback callee has). See the callback
       attribute documentation for detailed information.

Differential Revision: https://reviews.llvm.org/D55483

llvm-svn: 351629

1 files changed, 27 insertions, 0 deletions

diff --git a/clang/lib/Basic/Builtins.cpp b/clang/lib/Basic/Builtins.cpp
index 7e7f67ca874..53e7df95f81 100644
--- a/clang/lib/Basic/Builtins.cpp
+++ b/clang/lib/Basic/Builtins.cpp
@@ -156,6 +156,33 @@ bool Builtin::Context::isScanfLike(unsigned ID, unsigned &FormatIdx,
   return isLike(ID, FormatIdx, HasVAListArg, "sS");
 }
 
+bool Builtin::Context::performsCallback(unsigned ID,
+                                        SmallVectorImpl<int> &Encoding) const {
+  const char *CalleePos = ::strchr(getRecord(ID).Attributes, 'C');
+  if (!CalleePos)
+    return false;
+
+  ++CalleePos;
+  assert(*CalleePos == '<' &&
+         "Callback callee specifier must be followed by a '<'");
+  ++CalleePos;
+
+  char *EndPos;
+  int CalleeIdx = ::strtol(CalleePos, &EndPos, 10);
+  assert(CalleeIdx >= 0 && "Callee index is supposed to be positive!");
+  Encoding.push_back(CalleeIdx);
+
+  while (*EndPos == ',') {
+    const char *PayloadPos = EndPos + 1;
+
+    int PayloadIdx = ::strtol(PayloadPos, &EndPos, 10);
+    Encoding.push_back(PayloadIdx);
+  }
+
+  assert(*EndPos == '>' && "Callback callee specifier must end with a '>'");
+  return true;
+}
+
 bool Builtin::Context::canBeRedeclared(unsigned ID) const {
   return ID == Builtin::NotBuiltin ||
          ID == Builtin::BI__va_start ||