[midend-IVE]参考libdivide库，实现了魔数的正确求解，如果后续出错直接用API或者不要除法强度削弱了

src/midend/Pass/Optimize/LoopStrengthReduction.cpp

@@ -7,6 +7,8 @@
 #include <iostream>
 #include <algorithm>
 #include <cmath>
+#include <unordered_map>
+#include <climits>
 
 // 使用全局调试开关
 extern int DEBUG;
@@ -104,65 +106,188 @@ bool StrengthReductionContext::analyzeInductionVariableRange(
   return hasNegativePotential;
 }
 
-std::pair<int64_t, int> StrengthReductionContext::computeMulhMagicNumbers(int divisor) const {
-  // 计算用于除法的魔数 (magic number) 和移位量
-  // 基于 "Division by Invariant Integers using Multiplication" 算法
+//该实现参考了libdivide的算法
+std::pair<int, int> StrengthReductionContext::computeMulhMagicNumbers(int divisor) const {
   
-  int64_t magic = 0;
-  int shift = 0;
-  bool isPowerOfTwo = (divisor & (divisor - 1)) == 0;
-  
-  if (isPowerOfTwo) {
-    // 对于2的幂，不需要魔数，直接使用移位
-    magic = 1;
-    shift = __builtin_ctz(divisor); // 计算尾随零的个数
-    return {magic, shift};
+  if (DEBUG) {
+    std::cout << "\n[SR] ===== Computing magic numbers for divisor " << divisor << " (libdivide algorithm) =====" << std::endl;
   }
   
-  // 对于非2的幂的正数除数，计算魔数
-  // 使用32位有符号整数范围
-  const int bitWidth = 32;
-  const int64_t maxMagic = (1LL << (bitWidth - 1)) - 1;
+  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;
   
-  int64_t d = divisor;
-  int64_t nc = (1LL << (bitWidth - 1)) - (1LL << (bitWidth - 1)) % d;
-  int64_t delta = d - (1LL << (bitWidth - 1)) % d;
+  // 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);
+  };
   
-  shift = bitWidth - 1;
+  // 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;
   
-  // 找到合适的魔数和移位量
-  while (shift < bitWidth + 30) { // 避免无限循环
-    int64_t q1 = (1LL << shift) / nc;
-    int64_t r1 = (1LL << shift) - q1 * nc;
-    int64_t q2 = (1LL << shift) / delta;
-    int64_t r2 = (1LL << shift) - q2 * delta;
-    
-    if (q1 < q2 || (q1 == q2 && r1 < r2)) {
-      magic = q2 + 1;
-      if (magic <= maxMagic) {
-        break;
-      }
+  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;
     }
     
-    shift++;
-    nc = 2 * nc;
-    delta = 2 * delta;
+    // 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 (magic > maxMagic) {
-    // 回退到简单的魔数
-    magic = (1LL << bitWidth) / d + 1;
-    shift = bitWidth;
+  if (DEBUG) {
+    std::cout << "[SR] " << absD << " is not a power of 2, computing magic number" << std::endl;
   }
   
-  // 调整移位量以移除多余的2的幂因子
-  shift = shift - bitWidth;
-  if (shift < 0) shift = 0;
+  // 非2的幂除数的魔数计算
+  uint8_t more;
+  uint32_t rem, proposed_m;
   
-  return {magic, shift};
+  // 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()) {
     return false; // 空函数
@@ -651,7 +776,7 @@ bool StrengthReductionContext::createNewInductionVariable(StrengthReductionCandi
   // 2. 在循环头创建新的 phi 指令
   builder->setPosition(header, header->begin());
   candidate->newPhi = builder->createPhiInst(originalPhi->getType());
-  candidate->newPhi->setName(originalPhi->getName() + "_sr");
+  candidate->newPhi->setName("sr_" + originalPhi->getName());
 
   // 3. 计算新归纳变量的初始值和步长
   // 新IV的初始值 = 原IV初始值 * multiplier
@@ -895,14 +1020,35 @@ Value* StrengthReductionContext::generateConstantDivisionReplacement(
   // 使用mulh指令优化任意常数除法
   auto [magic, shift] = computeMulhMagicNumbers(candidate->multiplier);
   
-  if (magic == 1 && shift > 0) {
-    // 特殊情况：可以直接使用移位
-    Value* shiftConstant = ConstantInteger::get(shift);
+  // 检查是否无法优化（magic == -1, shift == -1 表示失败）
+  if (magic == -1 && shift == -1) {
+    if (DEBUG) {
+      std::cout << "[SR] Cannot optimize division by " << candidate->multiplier 
+                << ", keeping original division" << std::endl;
+    }
+    // 返回 nullptr 表示无法优化，调用方应该保持原始除法
+    return nullptr;
+  }
+  
+  // 2的幂次方除法可以用移位优化（但这不是魔数法的情况）这种情况应该不会被分类到这里但是还是做一个保护措施
+  if ((candidate->multiplier & (candidate->multiplier - 1)) == 0 && candidate->multiplier > 0) {
+    // 是2的幂次方，可以用移位
+    int shift_amount = 0;
+    int temp = candidate->multiplier;
+    while (temp > 1) {
+      temp >>= 1;
+      shift_amount++;
+    }
+    
+    Value* shiftConstant = ConstantInteger::get(shift_amount);
     if (candidate->hasNegativeValues) {
+      // 对于有符号除法，需要先加上除数-1然后再移位（为了正确处理负数舍入）
+      Value* divisor_minus_1 = ConstantInteger::get(candidate->multiplier - 1);
+      Value* adjusted = builder->createAddInst(candidate->inductionVar, divisor_minus_1);
       return builder->createBinaryInst(
         Instruction::Kind::kSra,  // 算术右移
         candidate->inductionVar->getType(),
-        candidate->inductionVar,
+        adjusted,
         shiftConstant
       );
     } else {
@@ -916,8 +1062,25 @@ Value* StrengthReductionContext::generateConstantDivisionReplacement(
   }
   
   // 创建魔数常量
+  // 检查魔数是否能放入32位，如果不能，则不进行优化
+  if (magic > INT32_MAX || magic < INT32_MIN) {
+    if (DEBUG) {
+      std::cout << "[SR] Magic number " << magic << " exceeds 32-bit range, skipping optimization" << std::endl;
+    }
+    return nullptr; // 无法优化，保持原始除法
+  }
+  
   Value* magicConstant = ConstantInteger::get((int32_t)magic);
   
+  // 检查是否需要ADD_MARKER处理（加法调整）
+  bool needAdd = (shift & 0x40) != 0;
+  int actualShift = shift & 0x3F; // 提取真实的移位量
+  
+  if (DEBUG) {
+    std::cout << "[SR] IR Generation: magic=" << magic << ", needAdd=" << needAdd 
+              << ", actualShift=" << actualShift << std::endl;
+  }
+  
   // 执行高位乘法：mulh(x, magic)
   Value* mulhResult = builder->createBinaryInst(
     Instruction::Kind::kMulh,  // 高位乘法
@@ -926,9 +1089,18 @@ Value* StrengthReductionContext::generateConstantDivisionReplacement(
     magicConstant
   );
   
-  if (shift > 0) {
+  if (needAdd) {
+    // ADD_MARKER 情况：需要在移位前加上被除数
+    // 这对应于 libdivide 的加法调整算法
+    if (DEBUG) {
+      std::cout << "[SR] Applying ADD_MARKER: adding dividend before shift" << std::endl;
+    }
+    mulhResult = builder->createAddInst(mulhResult, candidate->inductionVar);
+  }
+  
+  if (actualShift > 0) {
     // 如果需要额外移位
-    Value* shiftConstant = ConstantInteger::get(shift);
+    Value* shiftConstant = ConstantInteger::get(actualShift);
     mulhResult = builder->createBinaryInst(
       Instruction::Kind::kSra,  // 算术右移
       candidate->inductionVar->getType(),
@@ -937,14 +1109,11 @@ Value* StrengthReductionContext::generateConstantDivisionReplacement(
     );
   }
   
-  // 处理负数校正 - 简化版本
-  if (candidate->hasNegativeValues) {
-    // 简化处理：添加一个常数偏移来处理负数情况
-    // 这是一个简化的实现，实际的负数校正会更复杂
-    Value* zero = ConstantInteger::get(0);
-    Value* isNegative = builder->createICmpLTInst(candidate->inductionVar, zero);
-    // 这里应该有条件逻辑，但为了简化实现，暂时直接返回mulhResult
-  }
+  // 标准的有符号除法符号修正：如果被除数为负，商需要加1
+  // 这对所有有符号除法都需要，不管是否可能有负数
+  Value* isNegative = builder->createICmpLTInst(candidate->inductionVar, ConstantInteger::get(0));
+  // 将i1转换为i32：负数时为1，非负数时为0 ICmpLTInst的结果会默认转化为32位
+  mulhResult = builder->createAddInst(mulhResult, isNegative);
   
   return mulhResult;
 }