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[midend-GSR]将魔数求解移动到utils的静态方法中。

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This commit is contained in:
rain2133
2025-08-18 20:37:20 +08:00
parent c9a0c700e1
commit 5c34cbc7b8
6 changed files with 279 additions and 440 deletions
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183
src/midend/Pass/Optimize/LoopStrengthReduction.cpp
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@@ -106,187 +106,6 @@ bool StrengthReductionContext::analyzeInductionVariableRange(
return hasNegativePotential;
}
//该实现参考了libdivide的算法
std::pair<int, int> StrengthReductionContext::computeMulhMagicNumbers(int divisor) const {
if (DEBUG) {
std::cout << "\n[SR] ===== Computing magic numbers for divisor " << divisor << " (libdivide algorithm) =====" << std::endl;
}
if (divisor == 0) {
if (DEBUG) std::cout << "[SR] Error: divisor must be != 0" << std::endl;
return {-1, -1};
}
// libdivide 常数
const uint8_t LIBDIVIDE_ADD_MARKER = 0x40;
const uint8_t LIBDIVIDE_NEGATIVE_DIVISOR = 0x80;
// 辅助函数：计算前导零个数
auto count_leading_zeros32 = [](uint32_t val) -> uint32_t {
if (val == 0) return 32;
return __builtin_clz(val);
};
// 辅助函数：64位除法返回32位商和余数
auto div_64_32 = [](uint32_t high, uint32_t low, uint32_t divisor, uint32_t* rem) -> uint32_t {
uint64_t dividend = ((uint64_t)high << 32) | low;
uint32_t quotient = dividend / divisor;
*rem = dividend % divisor;
return quotient;
};
if (DEBUG) {
std::cout << "[SR] Input divisor: " << divisor << std::endl;
}
// libdivide_internal_s32_gen 算法实现
int32_t d = divisor;
uint32_t ud = (uint32_t)d;
uint32_t absD = (d < 0) ? -ud : ud;
if (DEBUG) {
std::cout << "[SR] absD = " << absD << std::endl;
}
uint32_t floor_log_2_d = 31 - count_leading_zeros32(absD);
if (DEBUG) {
std::cout << "[SR] floor_log_2_d = " << floor_log_2_d << std::endl;
}
// 检查 absD 是否为2的幂
if ((absD & (absD - 1)) == 0) {
if (DEBUG) {
std::cout << "[SR] " << absD << " 是2的幂，使用移位方法" << std::endl;
}
// 对于2的幂，我们只使用移位，不需要魔数
int shift = floor_log_2_d;
if (d < 0) shift |= 0x80; // 标记负数
if (DEBUG) {
std::cout << "[SR] Power of 2 result: magic=0, shift=" << shift << std::endl;
std::cout << "[SR] ===== End magic computation =====" << std::endl;
}
// 对于我们的目的，我们将在IR生成中以不同方式处理2的幂
// 返回特殊标记
return {0, shift};
}
if (DEBUG) {
std::cout << "[SR] " << absD << " is not a power of 2, computing magic number" << std::endl;
}
// 非2的幂除数的魔数计算
uint8_t more;
uint32_t rem, proposed_m;
// 计算 proposed_m = floor(2^(floor_log_2_d + 31) / absD)
proposed_m = div_64_32((uint32_t)1 << (floor_log_2_d - 1), 0, absD, &rem);
const uint32_t e = absD - rem;
if (DEBUG) {
std::cout << "[SR] proposed_m = " << proposed_m << ", rem = " << rem << ", e = " << e << std::endl;
}
// 确定是否需要"加法"版本
const bool branchfree = false; // 使用分支版本
if (!branchfree && e < ((uint32_t)1 << floor_log_2_d)) {
// 这个幂次有效
more = (uint8_t)(floor_log_2_d - 1);
if (DEBUG) {
std::cout << "[SR] Using basic algorithm, shift = " << (int)more << std::endl;
}
} else {
// 我们需要上升一个等级
proposed_m += proposed_m;
const uint32_t twice_rem = rem + rem;
if (twice_rem >= absD || twice_rem < rem) {
proposed_m += 1;
}
more = (uint8_t)(floor_log_2_d | LIBDIVIDE_ADD_MARKER);
if (DEBUG) {
std::cout << "[SR] Using add algorithm, proposed_m = " << proposed_m << ", more = " << (int)more << std::endl;
}
}
proposed_m += 1;
int32_t magic = (int32_t)proposed_m;
// 处理负除数
if (d < 0) {
more |= LIBDIVIDE_NEGATIVE_DIVISOR;
if (!branchfree) {
magic = -magic;
}
if (DEBUG) {
std::cout << "[SR] Negative divisor, magic = " << magic << ", more = " << (int)more << std::endl;
}
}
// 为我们的IR生成提取移位量和标志
int shift = more & 0x3F; // 移除标志，保留移位量（位0-5）
bool need_add = (more & LIBDIVIDE_ADD_MARKER) != 0;
bool is_negative = (more & LIBDIVIDE_NEGATIVE_DIVISOR) != 0;
if (DEBUG) {
std::cout << "[SR] Final result: magic = " << magic << ", more = " << (int)more
<< " (0x" << std::hex << (int)more << std::dec << ")" << std::endl;
std::cout << "[SR] Shift = " << shift << ", need_add = " << need_add
<< ", is_negative = " << is_negative << std::endl;
// Test the magic number using the correct libdivide algorithm
std::cout << "[SR] Testing magic number (libdivide algorithm):" << std::endl;
int test_values[] = {1, 7, 37, 100, 999, -1, -7, -37, -100};
for (int test_val : test_values) {
int64_t quotient;
// 实现正确的libdivide算法
int64_t product = (int64_t)test_val * magic;
int64_t high_bits = product >> 32;
if (need_add) {
// ADD_MARKER情况：移位前加上被除数
// 这是libdivide的关键洞察！
high_bits += test_val;
quotient = high_bits >> shift;
} else {
// 正常情况：只是移位
quotient = high_bits >> shift;
}
// 符号修正：这是libdivide有符号除法的关键部分！
// 如果被除数为负，商需要加1来匹配C语言的截断除法语义
if (test_val < 0) {
quotient += 1;
}
int expected = test_val / divisor;
bool correct = (quotient == expected);
std::cout << "[SR] " << test_val << " / " << divisor << " = " << quotient
<< " (expected " << expected << ") " << (correct ? "✓" : "✗") << std::endl;
}
std::cout << "[SR] ===== End magic computation =====" << std::endl;
}
// 返回魔数、移位量，并在移位中编码ADD_MARKER标志
// 我们将使用移位的第6位表示ADD_MARKER，第7位表示负数（如果需要）
int encoded_shift = shift;
if (need_add) {
encoded_shift |= 0x40; // 设置第6位表示ADD_MARKER
if (DEBUG) {
std::cout << "[SR] Encoding ADD_MARKER in shift: " << encoded_shift << std::endl;
}
}
return {magic, encoded_shift};
}
bool LoopStrengthReduction::runOnFunction(Function* F, AnalysisManager& AM) {
if (F->getBasicBlocks().empty()) {
@@ -1018,7 +837,7 @@ Value* StrengthReductionContext::generateConstantDivisionReplacement(
IRBuilder* builder
) const {
// 使用mulh指令优化任意常数除法
auto [magic, shift] = computeMulhMagicNumbers(candidate->multiplier);
auto [magic, shift] = SysYIROptUtils::computeMulhMagicNumbers(candidate->multiplier);
// 检查是否无法优化（magic == -1, shift == -1 表示失败）
if (magic == -1 && shift == -1) {