[PATCH] D96207: [FuzzMutate] Fix getWeight of InstDeleterIRStrategy

[Loris Reiff via Phabricator via llvm-commits]

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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.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D96207

Files:
  llvm/lib/FuzzMutate/IRMutator.cpp


Index: llvm/lib/FuzzMutate/IRMutator.cpp
===================================================================
--- llvm/lib/FuzzMutate/IRMutator.cpp
+++ llvm/lib/FuzzMutate/IRMutator.cpp
@@ -143,7 +143,10 @@
     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;


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