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Decompiler: Extend Rule2Comp2Sub to constants #8628

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Decompiler: Extend Rule2Comp2Sub to constants #8628

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@LukeSerne LukeSerne commented Nov 15, 2025

Before, the cleanup rule Rule2Comp2Sub only worked on explicit negations that used INT_2COMP. However, subtractions with constants are also replaced by additions during decompilation. This resulted in decompiler output like x + -1. With this change, constants are also considered. As such, the same example now looks like x - 1.

Before

void DecreaseValue(struct *param_1,int param_2)

{
  int new_value;

  if (param_1->mItems[param_2].mIsActive == true)
  {
    new_value = param_1->mItems[param_2].mValue + -0x1a;
    param_1->mItems[param_2].mValue = new_value;
  }
  return;
}

After

void DecreaseValue(struct *param_1,int param_2)

{
  int new_value;

  if (param_1->mItems[param_2].mIsActive == true)
  {
    new_value = param_1->mItems[param_2].mValue - 0x1a;
    param_1->mItems[param_2].mValue = new_value;
  }
  return;
}

@LukeSerne
Decompiler: Extend Rule2Comp2Sub to constants
cdd380d 
Before, Rule2Comp2Sub only worked on explicit negations using INT_2COMP,
but subtractions with constants are also replaced by additions during
decompilation. This resulted in decompiler output like "x + -1". With
this change, constants are also considered. As such, the same example
now looks like "x - 1".
@ryanmkurtz ryanmkurtz added Feature: Decompiler Status: Triage Information is being gathered labels Nov 17, 2025
@LukeSerne
Ensure no dangling INT_2COMPs remain
7d6f865 
If we have removed the only output of the INT_2COMP, remove the op as
well to avoid useless statements appearing in the final decompiled code.
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Feature: Decompiler Status: Triage Information is being gathered

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@LukeSerne @ryanmkurtz @caheckman