[llvm] r250240 - Update MachineBranchProbabilityInfo::normalizeEdgeWeights to make sure there is no zero weight in the output, and also add a missing test for JumpThreading.

[Manman Ren via llvm-commits]

Our internal bot is still failing with this:
Assertion failed: (Sum >= PrevSum), function getSumForBlock, file /Users/buildslave/jenkins/sharedspace/apple-clang-stage2-RA at 2/clang/src/lib/Analysis/BranchProbabilityInfo.cpp, line 533.

clang: error: unable to execute command: Illegal instruction: 4

I am going to revert this and 250204.

I will give you a reduced testing case, so you can work on the fix tomorrow.

Thanks,
Manman

> On Oct 13, 2015, at 3:27 PM, Cong Hou via llvm-commits <llvm-commits at lists.llvm.org> wrote:
> 
> Author: conghou
> Date: Tue Oct 13 17:27:41 2015
> New Revision: 250240
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=250240&view=rev
> Log:
> Update MachineBranchProbabilityInfo::normalizeEdgeWeights to make sure there is no zero weight in the output, and also add a missing test for JumpThreading.
> 
> The test is for the patch in http://reviews.llvm.org/D10979 but was missing when committing that patch.
> 
> 
> Added:
>    llvm/trunk/test/Transforms/JumpThreading/update-edge-weight.ll
> Modified:
>    llvm/trunk/include/llvm/CodeGen/MachineBranchProbabilityInfo.h
> 
> Modified: llvm/trunk/include/llvm/CodeGen/MachineBranchProbabilityInfo.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/CodeGen/MachineBranchProbabilityInfo.h?rev=250240&r1=250239&r2=250240&view=diff
> ==============================================================================
> --- llvm/trunk/include/llvm/CodeGen/MachineBranchProbabilityInfo.h (original)
> +++ llvm/trunk/include/llvm/CodeGen/MachineBranchProbabilityInfo.h Tue Oct 13 17:27:41 2015
> @@ -86,35 +86,43 @@ public:
>                                     const MachineBasicBlock *Dst) const;
> 
>   // Normalize a list of weights by scaling them down so that the sum of them
> -  // doesn't exceed UINT32_MAX. Return the scale.
> +  // doesn't exceed UINT32_MAX.
>   template <class WeightListIter>
> -  static uint32_t normalizeEdgeWeights(WeightListIter Begin,
> -                                       WeightListIter End);
> +  static void normalizeEdgeWeights(WeightListIter Begin, WeightListIter End);
> };
> 
> template <class WeightListIter>
> -uint32_t
> -MachineBranchProbabilityInfo::normalizeEdgeWeights(WeightListIter Begin,
> -                                                   WeightListIter End) {
> +void MachineBranchProbabilityInfo::normalizeEdgeWeights(WeightListIter Begin,
> +                                                        WeightListIter End) {
>   // First we compute the sum with 64-bits of precision.
>   uint64_t Sum = std::accumulate(Begin, End, uint64_t(0));
> 
> -  // If Sum is zero, set all weights to 1.
> -  if (Sum == 0)
> -    std::fill(Begin, End, uint64_t(1));
> -
> -  // If the computed sum fits in 32-bits, we're done.
> -  if (Sum <= UINT32_MAX)
> -    return 1;
> -
> -  // Otherwise, compute the scale necessary to cause the weights to fit, and
> -  // re-sum with that scale applied.
> -  assert((Sum / UINT32_MAX) < UINT32_MAX &&
> -         "The sum of weights exceeds UINT32_MAX^2!");
> -  uint32_t Scale = (Sum / UINT32_MAX) + 1;
> -  for (auto I = Begin; I != End; ++I)
> -    *I /= Scale;
> -  return Scale;
> +  if (Sum > UINT32_MAX) {
> +    // Compute the scale necessary to cause the weights to fit, and re-sum with
> +    // that scale applied.
> +    assert(Sum / UINT32_MAX < UINT32_MAX &&
> +           "The sum of weights exceeds UINT32_MAX^2!");
> +    uint32_t Scale = Sum / UINT32_MAX + 1;
> +    for (auto I = Begin; I != End; ++I)
> +      *I /= Scale;
> +    Sum = std::accumulate(Begin, End, uint64_t(0));
> +  }
> +
> +  // Eliminate zero weights.
> +  auto ZeroWeightNum = std::count(Begin, End, 0u);
> +  if (ZeroWeightNum > 0) {
> +    // If all weights are zeros, replace them by 1.
> +    if (Sum == 0)
> +      std::fill(Begin, End, 1u);
> +    else {
> +      // Scale up non-zero weights and turn zero weights into ones.
> +      uint64_t ScalingFactor = (UINT32_MAX - ZeroWeightNum) / Sum;
> +      if (ScalingFactor > 1)
> +        for (auto I = Begin; I != End; ++I)
> +          *I *= ScalingFactor;
> +      std::replace(Begin, End, 0u, 1u);
> +    }
> +  }
> }
> 
> }
> 
> Added: llvm/trunk/test/Transforms/JumpThreading/update-edge-weight.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/JumpThreading/update-edge-weight.ll?rev=250240&view=auto
> ==============================================================================
> --- llvm/trunk/test/Transforms/JumpThreading/update-edge-weight.ll (added)
> +++ llvm/trunk/test/Transforms/JumpThreading/update-edge-weight.ll Tue Oct 13 17:27:41 2015
> @@ -0,0 +1,43 @@
> +; RUN: opt -S -jump-threading %s | FileCheck %s
> +
> +; Test if edge weights are properly updated after jump threading.
> +
> +; CHECK: !2 = !{!"branch_weights", i32 22, i32 7}
> +
> +define void @foo(i32 %n) !prof !0 {
> +entry:
> +  %cmp = icmp sgt i32 %n, 10
> +  br i1 %cmp, label %if.then.1, label %if.else.1, !prof !1
> +
> +if.then.1:
> +  tail call void @a()
> +  br label %if.cond
> +
> +if.else.1:
> +  tail call void @b()
> +  br label %if.cond
> +
> +if.cond:
> +  %cmp1 = icmp sgt i32 %n, 5
> +  br i1 %cmp1, label %if.then.2, label %if.else.2, !prof !2
> +
> +if.then.2:
> +  tail call void @c()
> +  br label %if.end
> +
> +if.else.2:
> +  tail call void @d()
> +  br label %if.end
> +
> +if.end:
> +  ret void
> +}
> +
> +declare void @a()
> +declare void @b()
> +declare void @c()
> +declare void @d()
> +
> +!0 = !{!"function_entry_count", i64 1}
> +!1 = !{!"branch_weights", i32 10, i32 5}
> +!2 = !{!"branch_weights", i32 10, i32 1}
> 
> 
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