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VarAction2: Detect and replace operations which always produce 0

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This commit is contained in:
Jonathan G Rennison
2022-05-25 20:04:36 +01:00
parent a21ae12c90
commit 3b5eede3fc
2 changed files with 47 additions and 0 deletions
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21
src/newgrf.cpp
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@@ -5677,6 +5677,27 @@ static void NewSpriteGroup(ByteReader *buf)
/* Delete useless zero operations */
group->adjusts.pop_back();
inference = prev_inference;
} else if (adjust.and_mask == 0 && IsEvalAdjustWithZeroAlwaysZero(adjust.operation)) {
/* Operation always returns 0, replace it and any useless prior operations */
group->adjusts.pop_back();
while (!group->adjusts.empty()) {
const DeterministicSpriteGroupAdjust &prev = group->adjusts.back();
if (prev.variable != 0x7E && !IsEvalAdjustWithSideEffects(prev.operation)) {
/* Delete useless operation */
group->adjusts.pop_back();
} else {
break;
}
}
DeterministicSpriteGroupAdjust &replacement = group->adjusts.emplace_back();
replacement.operation = group->adjusts.size() == 1 ? DSGA_OP_ADD : DSGA_OP_RST;
replacement.variable = 0x1A;
replacement.shift_num = 0;
replacement.type = DSGA_TYPE_NONE;
replacement.and_mask = 0;
replacement.add_val = 0;
replacement.divmod_val = 0;
inference = VA2AIF_SIGNED_NON_NEGATIVE | VA2AIF_ONE_OR_ZERO | VA2AIF_PREV_MASK_ADJUST;
} else {
switch (adjust.operation) {
case DSGA_OP_SMIN: