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constant_propagation_pass: Propagate constants across commutative operations

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e.g. (a & b) & c == a & (b & c) where b and c are constants
This commit is contained in:
MerryMage 2020-04-20 19:04:01 +01:00
parent f59b9fb020
commit 0d7476d3ec
2 changed files with 63 additions and 54 deletions
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18
src/frontend/ir/value.cpp
View file

@ -213,23 +213,7 @@ bool Value::IsUnsignedImmediate(u64 value) const {
}
bool Value::HasAllBitsSet() const {
ASSERT(IsImmediate());
switch (GetType()) {
case IR::Type::U1:
return GetU1();
case IR::Type::U8:
return GetU8() == 0xFF;
case IR::Type::U16:
return GetU16() == 0xFFFF;
case IR::Type::U32:
return GetU32() == 0xFFFFFFFF;
case IR::Type::U64:
return GetU64() == 0xFFFFFFFFFFFFFFFF;
default:
ASSERT_MSG(false, "HasAllBitsSet called on an incompatible Value type.");
return false;
}
return IsSignedImmediate(-1);
}
bool Value::IsZero() const {

87
src/ir_opt/constant_propagation_pass.cpp
View file

@ -23,6 +23,49 @@ void ReplaceUsesWith(IR::Inst& inst, bool is_32_bit, u64 value) {
}
}
IR::Value Value(bool is_32_bit, u64 value) {
return is_32_bit ? IR::Value{static_cast<u32>(value)} : IR::Value{value};
}
template <typename ImmFn>
bool FoldCommutative(IR::Inst& inst, bool is_32_bit, ImmFn imm_fn) {
const auto lhs = inst.GetArg(0);
const auto rhs = inst.GetArg(1);
const bool is_lhs_immediate = lhs.IsImmediate();
const bool is_rhs_immediate = rhs.IsImmediate();
if (is_lhs_immediate && is_rhs_immediate) {
const u64 result = imm_fn(lhs.GetImmediateAsU64(), rhs.GetImmediateAsU64());
ReplaceUsesWith(inst, is_32_bit, result);
return false;
}
if (is_lhs_immediate && !is_rhs_immediate) {
const IR::Inst* rhs_inst = rhs.GetInstRecursive();
if (rhs_inst->GetOpcode() == inst.GetOpcode() && rhs_inst->GetArg(1).IsImmediate()) {
const u64 combined = imm_fn(lhs.GetImmediateAsU64(), rhs_inst->GetArg(1).GetImmediateAsU64());
inst.SetArg(0, rhs_inst->GetArg(0));
inst.SetArg(1, Value(is_32_bit, combined));
} else {
// Normalize
inst.SetArg(0, rhs);
inst.SetArg(1, lhs);
}
}
if (!is_lhs_immediate && is_rhs_immediate) {
const IR::Inst* lhs_inst = lhs.GetInstRecursive();
if (lhs_inst->GetOpcode() == inst.GetOpcode() && lhs_inst->GetArg(1).IsImmediate()) {
const u64 combined = imm_fn(rhs.GetImmediateAsU64(), lhs_inst->GetArg(1).GetImmediateAsU64());
inst.SetArg(0, lhs_inst->GetArg(0));
inst.SetArg(1, Value(is_32_bit, combined));
}
}
return true;
}
// Folds AND operations based on the following:
//
// 1. imm_x & imm_y -> result
@ -32,21 +75,13 @@ void ReplaceUsesWith(IR::Inst& inst, bool is_32_bit, u64 value) {
// 5. x & y -> x (where y has all bits set to 1)
//
void FoldAND(IR::Inst& inst, bool is_32_bit) {
const auto lhs = inst.GetArg(0);
if (FoldCommutative(inst, is_32_bit, [](u64 a, u64 b) { return a & b; })) {
const auto rhs = inst.GetArg(1);
const bool is_lhs_immediate = lhs.IsImmediate();
const bool is_rhs_immediate = rhs.IsImmediate();
if (is_lhs_immediate && is_rhs_immediate) {
const u64 result = lhs.GetImmediateAsU64() & rhs.GetImmediateAsU64();
ReplaceUsesWith(inst, is_32_bit, result);
} else if (lhs.IsZero() || rhs.IsZero()) {
if (rhs.IsZero()) {
ReplaceUsesWith(inst, is_32_bit, 0);
} else if (is_lhs_immediate && lhs.HasAllBitsSet()) {
inst.ReplaceUsesWith(rhs);
} else if (is_rhs_immediate && rhs.HasAllBitsSet()) {
inst.ReplaceUsesWith(lhs);
} else if (rhs.HasAllBitsSet()) {
inst.ReplaceUsesWith(inst.GetArg(0));
}
}
}
@ -108,16 +143,11 @@ void FoldDivide(IR::Inst& inst, bool is_32_bit, bool is_signed) {
// 3. 0 ^ y -> y
//
void FoldEOR(IR::Inst& inst, bool is_32_bit) {
const auto lhs = inst.GetArg(0);
if (FoldCommutative(inst, is_32_bit, [](u64 a, u64 b) { return a ^ b; })) {
const auto rhs = inst.GetArg(1);
if (lhs.IsImmediate() && rhs.IsImmediate()) {
const u64 result = lhs.GetImmediateAsU64() ^ rhs.GetImmediateAsU64();
ReplaceUsesWith(inst, is_32_bit, result);
} else if (lhs.IsZero()) {
inst.ReplaceUsesWith(rhs);
} else if (rhs.IsZero()) {
inst.ReplaceUsesWith(lhs);
if (rhs.IsZero()) {
inst.ReplaceUsesWith(inst.GetArg(0));
}
}
}
@ -180,18 +210,13 @@ void FoldMostSignificantWord(IR::Inst& inst) {
// 5. 1 * y -> y
//
void FoldMultiply(IR::Inst& inst, bool is_32_bit) {
const auto lhs = inst.GetArg(0);
if (FoldCommutative(inst, is_32_bit, [](u64 a, u64 b) { return a * b; })) {
const auto rhs = inst.GetArg(1);
if (lhs.IsImmediate() && rhs.IsImmediate()) {
const u64 result = lhs.GetImmediateAsU64() * rhs.GetImmediateAsU64();
ReplaceUsesWith(inst, is_32_bit, result);
} else if (lhs.IsZero() || rhs.IsZero()) {
if (rhs.IsZero()) {
ReplaceUsesWith(inst, is_32_bit, 0);
} else if (lhs.IsUnsignedImmediate(1)) {
inst.ReplaceUsesWith(rhs);
} else if (rhs.IsUnsignedImmediate(1)) {
inst.ReplaceUsesWith(lhs);
inst.ReplaceUsesWith(inst.GetArg(0));
}
}
}