[llvm-commits] [llvm] r132613 - in /llvm/trunk: include/llvm/Analysis/BranchProbabilityInfo.h include/llvm/InitializePasses.h lib/Analysis/Analysis.cpp lib/Analysis/BranchProbabilityInfo.cpp lib/Analysis/CMakeLists.txt

[Alistair Lynn]

Hi-

Given that

> +  // Returned value is between 1 and UINT_MAX. Look at BranchProbabilityInfo.cpp
> +  // for details.

Is this function not prone to integer overflow issues?

> +// TODO: This currently hardcodes 80% as a fraction 4/5. We will soon add a
> +// BranchProbability class to encapsulate the fractional probability and
> +// define a few static instances of the class for use as predefined thresholds.
> +bool BranchProbabilityInfo::isEdgeHot(BasicBlock *Src, BasicBlock *Dst) const {
> +  unsigned Sum = 0;
> +  for (succ_iterator I = succ_begin(Src), E = succ_end(Src); I != E; ++I) {
> +    BasicBlock *Succ = *I;
> +    unsigned Weight = getEdgeWeight(Src, Succ);
> +    unsigned PrevSum = Sum;
> +
> +    Sum += Weight;
> +    assert(Sum > PrevSum); (void) PrevSum;
> +  }
> +
> +  return getEdgeWeight(Src, Dst) * 5 > Sum * 4;
> +}

The sum itself is checked for overflow in the assert, but surely there's nothing preventing overflow on the multiplies on the condition at the end?

Alistair