[llvm] r341444 - Prevent unsigned overflow.

[Richard Trieu via llvm-commits]

Author: rtrieu
Date: Tue Sep  4 21:19:15 2018
New Revision: 341444

URL: http://llvm.org/viewvc/llvm-project?rev=341444&view=rev
Log:
Prevent unsigned overflow.

The sum of the weights is caculated in an APInt, which has a width smaller than
64.  In certain cases, the sum of the widths would overflow when calculations
are done inside an APInt, but would not if done with uint64_t.  Since the
values will be passed as uint64_t in the function call anyways, do all the math
in 64 bits.  Also added an assert in case the probabilities overflow 64 bits.

Modified:
    llvm/trunk/lib/Transforms/Instrumentation/ControlHeightReduction.cpp

Modified: llvm/trunk/lib/Transforms/Instrumentation/ControlHeightReduction.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Instrumentation/ControlHeightReduction.cpp?rev=341444&r1=341443&r2=341444&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Instrumentation/ControlHeightReduction.cpp (original)
+++ llvm/trunk/lib/Transforms/Instrumentation/ControlHeightReduction.cpp Tue Sep  4 21:19:15 2018
@@ -614,13 +614,15 @@ static bool CheckMDProf(MDNode *MD, Bran
   ConstantInt *FalseWeight = mdconst::extract<ConstantInt>(MD->getOperand(2));
   if (!TrueWeight || !FalseWeight)
     return false;
-  APInt TrueWt = TrueWeight->getValue();
-  APInt FalseWt = FalseWeight->getValue();
-  APInt SumWt = TrueWt + FalseWt;
-  TrueProb = BranchProbability::getBranchProbability(TrueWt.getZExtValue(),
-                                                     SumWt.getZExtValue());
-  FalseProb = BranchProbability::getBranchProbability(FalseWt.getZExtValue(),
-                                                      SumWt.getZExtValue());
+  uint64_t TrueWt = TrueWeight->getValue().getZExtValue();
+  uint64_t FalseWt = FalseWeight->getValue().getZExtValue();
+  uint64_t SumWt = TrueWt + FalseWt;
+
+  assert(SumWt >= TrueWt && SumWt >= FalseWt &&
+         "Overflow calculating branch probabilities.");
+
+  TrueProb = BranchProbability::getBranchProbability(TrueWt, SumWt);
+  FalseProb = BranchProbability::getBranchProbability(FalseWt, SumWt);
   return true;
 }