[XRay] Bug fixes for FDR custom event and arg-logging

Summary:
This change has a number of fixes for FDR mode in compiler-rt along with
changes to the tooling handling the traces in llvm.

In the runtime, we do the following:

- Advance the "last record" pointer appropriately when writing the
  custom event data in the log.

- Add XRAY_NEVER_INSTRUMENT in the rewinding routine.

- When collecting the argument of functions appropriately marked, we
  should not attempt to rewind them (and reset the counts of functions
  that can be re-wound).

In the tooling, we do the following:

- Remove the state logic in BlockIndexer and instead rely on the
  presence/absence of records to indicate blocks.

- Move the verifier into a loop associated with each block.

Reviewers: mboerger, eizan

Subscribers: llvm-commits, hiraditya

Differential Revision: https://reviews.llvm.org/D51965

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@342122 91177308-0d34-0410-b5e6-96231b3b80d8

lib/XRay/BlockIndexer.cpp

@@ -16,22 +16,7 @@
 namespace llvm {
 namespace xray {
 
-Error BlockIndexer::visit(BufferExtents &) {
-  if (CurrentState == State::ThreadIDFound) {
-    Index::iterator It;
-    std::tie(It, std::ignore) =
-        Indices.insert({{CurrentBlock.ProcessID, CurrentBlock.ThreadID}, {}});
-    It->second.push_back({CurrentBlock.ProcessID, CurrentBlock.ThreadID,
-                          CurrentBlock.WallclockTime,
-                          std::move(CurrentBlock.Records)});
-    CurrentBlock.ProcessID = 0;
-    CurrentBlock.ThreadID = 0;
-    CurrentBlock.WallclockTime = nullptr;
-    CurrentBlock.Records = {};
-  }
-  CurrentState = State::ExtentsFound;
-  return Error::success();
-}
+Error BlockIndexer::visit(BufferExtents &) { return Error::success(); }
 
 Error BlockIndexer::visit(WallclockRecord &R) {
   CurrentBlock.Records.push_back(&R);
@@ -66,14 +51,16 @@ Error BlockIndexer::visit(PIDRecord &R) {
 }
 
 Error BlockIndexer::visit(NewBufferRecord &R) {
-  CurrentState = State::ThreadIDFound;
+  if (!CurrentBlock.Records.empty())
+    if (auto E = flush())
+      return E;
+
   CurrentBlock.ThreadID = R.tid();
   CurrentBlock.Records.push_back(&R);
   return Error::success();
 }
 
 Error BlockIndexer::visit(EndBufferRecord &R) {
-  CurrentState = State::SeekExtents;
   CurrentBlock.Records.push_back(&R);
   return Error::success();
 }
@@ -84,7 +71,6 @@ Error BlockIndexer::visit(FunctionRecord &R) {
 }
 
 Error BlockIndexer::flush() {
-  CurrentState = State::SeekExtents;
   Index::iterator It;
   std::tie(It, std::ignore) =
       Indices.insert({{CurrentBlock.ProcessID, CurrentBlock.ThreadID}, {}});
@@ -94,6 +80,7 @@ Error BlockIndexer::flush() {
   CurrentBlock.ProcessID = 0;
   CurrentBlock.ThreadID = 0;
   CurrentBlock.Records = {};
+  CurrentBlock.WallclockTime = nullptr;
   return Error::success();
 }