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[FuzzMutate] Fix getWeight of InstDeleterIRStrategy

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The comment states the following, for calculating the Line variable:

> Draw a line starting from when we only have 1k left and increasing
> linearly to double the current weight.

However, the value was not calculated as described. Instead, it would
result in a negative value, which resulted in the function always
returning 0 afterwards.

```
// Invariant: CurrentSize <= MaxSize - 200
// Invariant: CurrentWeight >= 0
int Line = (-2 * CurrentWeight) * (MaxSize - CurrentSize + 1000);
// {Line <= 0}
```

This commit fixes the issue and linearly interpolates as described.

Patch by Loris Reiff. Thanks!

Differential Revision: https://reviews.llvm.org/D96207
This commit is contained in:
Justin Bogner 2021-06-08 11:14:33 -07:00
parent 42052632ff
commit 880a1f20ab
1 changed files with 4 additions and 1 deletions
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5
lib/FuzzMutate/IRMutator.cpp
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@ -143,7 +143,10 @@ uint64_t InstDeleterIRStrategy::getWeight(size_t CurrentSize, size_t MaxSize,
return CurrentWeight ? CurrentWeight * 100 : 1;
// Draw a line starting from when we only have 1k left and increasing linearly
// to double the current weight.
int Line = (-2 * CurrentWeight) * (MaxSize - CurrentSize + 1000);
int64_t Line = (-2 * static_cast<int64_t>(CurrentWeight)) *
(static_cast<int64_t>(MaxSize) -
static_cast<int64_t>(CurrentSize) - 1000) /
1000;
// Clamp negative weights to zero.
if (Line < 0)
return 0;