[llvm] r277849 - [AutoFDO] Fix handling of empty profiles

[David Callahan via llvm-commits]

Author: david2050
Date: Fri Aug  5 13:38:19 2016
New Revision: 277849

URL: http://llvm.org/viewvc/llvm-project?rev=277849&view=rev
Log:
[AutoFDO] Fix handling of empty profiles

Summary:
If a profile has no samples for a function, then the function "entry count" is set to the value 0. Several places in the code test that if the Function::getEntryCount is defined at all. Here we change to treat a 0 entry count the same as undefined.

In particular, this fixes a problem in getLayoutSuccessorProbThreshold in MachineBlockPlacement.cpp where we use a different and inferior heuristic for laying out basic blocks.

Reviewers: danielcdh, dnovillo

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D23082

Modified:
    llvm/trunk/lib/IR/Function.cpp

Modified: llvm/trunk/lib/IR/Function.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/Function.cpp?rev=277849&r1=277848&r2=277849&view=diff
==============================================================================
--- llvm/trunk/lib/IR/Function.cpp (original)
+++ llvm/trunk/lib/IR/Function.cpp Fri Aug  5 13:38:19 2016
@@ -1262,7 +1262,10 @@ Optional<uint64_t> Function::getEntryCou
     if (MDString *MDS = dyn_cast<MDString>(MD->getOperand(0)))
       if (MDS->getString().equals("function_entry_count")) {
         ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(1));
-        return CI->getValue().getZExtValue();
+        uint64_t Count = CI->getValue().getZExtValue();
+        if (Count == 0)
+          return None;
+        return Count;
       }
   return None;
 }