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Un-recursify OptimizeInstructions::optimizeAddedConstants #2157

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kripken merged 2 commits into from
Jun 1, 2019
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Un-recursify OptimizeInstructions::optimizeAddedConstants #2157

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un-recursify OptimizeInstructions::optimizeAddedConstants to avoid is…
kripken Jun 1, 2019
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kripken Jun 1, 2019
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43 changes: 27 additions & 16 deletions src/passes/OptimizeInstructions.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -986,46 +986,57 @@ struct OptimizeInstructions
Expression* optimizeAddedConstants(Binary* binary) {
uint32_t constant = 0;
std::vector<Const*> constants;
std::function<void(Expression*, int)> seek = [&](Expression* curr,
int mul) {

struct SeekState {
Expression* curr;
int mul;
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@dschuff dschuff Jun 1, 2019

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I guess this is pre-existing, but is 'mul' short for 'multiplier'? Could we maybe spend a few of our 80 columns and spell it out?

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@dschuff dschuff Jun 1, 2019

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oh, it makes more sense if you expand and read the function comment. either way.

SeekState(Expression* curr, int mul) : curr(curr), mul(mul) {}
};
std::vector<SeekState> seekStack;
seekStack.emplace_back(binary, 1);
while (!seekStack.empty()) {
auto state = seekStack.back();
seekStack.pop_back();
auto curr = state.curr;
auto mul = state.mul;
if (auto* c = curr->dynCast<Const>()) {
uint32_t value = c->value.geti32();
if (value != 0) {
constant += value * mul;
constants.push_back(c);
}
return;
continue;
} else if (auto* binary = curr->dynCast<Binary>()) {
if (binary->op == AddInt32) {
seek(binary->left, mul);
seek(binary->right, mul);
return;
seekStack.emplace_back(binary->right, mul);
seekStack.emplace_back(binary->left, mul);
continue;
} else if (binary->op == SubInt32) {
// if the left is a zero, ignore it, it's how we negate ints
auto* left = binary->left->dynCast<Const>();
seekStack.emplace_back(binary->right, -mul);
if (!left || left->value.geti32() != 0) {
seek(binary->left, mul);
seekStack.emplace_back(binary->left, mul);
}
seek(binary->right, -mul);
return;
continue;
} else if (binary->op == ShlInt32) {
if (auto* c = binary->right->dynCast<Const>()) {
seek(binary->left, mul * Pow2(Bits::getEffectiveShifts(c)));
return;
seekStack.emplace_back(binary->left,
mul * Pow2(Bits::getEffectiveShifts(c)));
continue;
}
} else if (binary->op == MulInt32) {
if (auto* c = binary->left->dynCast<Const>()) {
seek(binary->right, mul * c->value.geti32());
return;
seekStack.emplace_back(binary->right, mul * c->value.geti32());
continue;
} else if (auto* c = binary->right->dynCast<Const>()) {
seek(binary->left, mul * c->value.geti32());
return;
seekStack.emplace_back(binary->left, mul * c->value.geti32());
continue;
}
}
}
};
// find all factors
seek(binary, 1);
if (constants.size() <= 1) {
// nothing much to do, except for the trivial case of adding/subbing a
// zero
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