[XRAY] [compiler-rt] [NFC] Fixing the bit twiddling of Function Id in…

… FDR logging mode.

Summary:
Fixing a bug I found when testing a reader for the FDR format. Function ID is
now correctly packed into the 28 bits which are documented for it instead of being
masked to all ones.

Reviewers: dberris, pelikan, eugenis

Reviewed By: dberris

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D29698

llvm-svn: 294563

compiler-rt/lib/xray/xray_fdr_logging.cc

@@ -459,7 +459,7 @@ void fdrLoggingHandleArg0(int32_t FuncId,
   FuncRecord.Type = RecordType::Function;
 
   // Only get the lower 28 bits of the function id.
-  FuncRecord.FuncId = FuncId | ~(0x03 << 28);
+  FuncRecord.FuncId = FuncId & ~(0x0F << 28);
 
   // Here we compute the TSC Delta. There are a few interesting situations we
   // need to account for: