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constant_propagation_pass: Fold Mul32 and Mul64 cases where applicable

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Multiplication operations can currently be folded if:

1. Both arguments are known constant values
2. Either operand is zero (in which case the result is also zero)
3. Either operand is one (in which case the result is the non-one
operand).
This commit is contained in:
Lioncash 2018-10-07 21:48:42 -04:00 committed by MerryMage
parent 546cfbc0ee
commit 72daf37208
1 changed files with 37 additions and 0 deletions
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37
src/ir_opt/constant_propagation_pass.cpp
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@ -74,6 +74,39 @@ void FoldEOR(IR::Inst& inst, bool is_32_bit) {
}
}
// Folds multiplication operations based on the following:
//
// 1. imm_x * imm_y -> result
// 2. x * 0 -> 0
// 3. 0 * y -> 0
// 4. x * 1 -> x
// 5. 1 * y -> y
//
void FoldMultiply(IR::Inst& inst, bool is_32_bit) {
const auto lhs = inst.GetArg(0);
const auto rhs = inst.GetArg(1);
if (lhs.IsImmediate() && rhs.IsImmediate()) {
const u64 result = lhs.GetImmediateAsU64() * rhs.GetImmediateAsU64();
if (is_32_bit) {
inst.ReplaceUsesWith(IR::Value{static_cast<u32>(result)});
} else {
inst.ReplaceUsesWith(IR::Value{result});
}
} else if (lhs.IsZero() || rhs.IsZero()) {
if (is_32_bit) {
inst.ReplaceUsesWith(IR::Value{u32{0}});
} else {
inst.ReplaceUsesWith(IR::Value{u64{0}});
}
} else if (lhs.IsUnsignedImmediate(1)) {
inst.ReplaceUsesWith(rhs);
} else if (rhs.IsUnsignedImmediate(1)) {
inst.ReplaceUsesWith(lhs);
}
}
// Folds NOT operations if the contained value is an immediate.
void FoldNOT(IR::Inst& inst, bool is_32_bit) {
const auto operand = inst.GetArg(0);
@ -174,6 +207,10 @@ void ConstantPropagation(IR::Block& block) {
}
break;
}
case IR::Opcode::Mul32:
case IR::Opcode::Mul64:
FoldMultiply(inst, opcode == IR::Opcode::Mul32);
break;
case IR::Opcode::And32:
case IR::Opcode::And64:
FoldAND(inst, opcode == IR::Opcode::And32);