[ADT][APInt] add sfloordiv_ov APInt's member function (#84720)

for mlir fold to avoid too many overflow state check

Author: lipracer

llvm/include/llvm/ADT/APInt.h

@@ -997,6 +997,12 @@ class [[nodiscard]] APInt {
   APInt ushl_ov(const APInt &Amt, bool &Overflow) const;
   APInt ushl_ov(unsigned Amt, bool &Overflow) const;
 
+  /// Signed integer floor division operation.
+  ///
+  /// Rounds towards negative infinity, i.e. 5 / -2 = -3. Iff minimum value
+  /// divided by -1 set Overflow to true.
+  APInt sfloordiv_ov(const APInt &RHS, bool &Overflow) const;
+
   // Operations that saturate
   APInt sadd_sat(const APInt &RHS) const;
   APInt uadd_sat(const APInt &RHS) const;

llvm/lib/Support/APInt.cpp

@@ -2022,6 +2022,13 @@ APInt APInt::ushl_ov(unsigned ShAmt, bool &Overflow) const {
   return *this << ShAmt;
 }
 
+APInt APInt::sfloordiv_ov(const APInt &RHS, bool &Overflow) const {
+  APInt quotient = sdiv_ov(RHS, Overflow);
+  if ((quotient * RHS != *this) && (isNegative() != RHS.isNegative()))
+    return quotient - 1;
+  return quotient;
+}
+
 APInt APInt::sadd_sat(const APInt &RHS) const {
   bool Overflow;
   APInt Res = sadd_ov(RHS, Overflow);

llvm/unittests/ADT/APIntTest.cpp

@@ -15,6 +15,7 @@
 #include "gtest/gtest.h"
 #include <array>
 #include <climits>
+#include <limits>
 #include <optional>
 
 using namespace llvm;
@@ -3048,6 +3049,69 @@ TEST(APIntTest, smul_ov) {
       }
 }
 
+TEST(APIntTest, sfloordiv_ov) {
+  // int16 test overflow
+  {
+    using IntTy = int16_t;
+    APInt divisor(8 * sizeof(IntTy), std::numeric_limits<IntTy>::lowest(),
+                  true);
+    APInt dividend(8 * sizeof(IntTy), IntTy(-1), true);
+    bool Overflow = false;
+    (void)divisor.sfloordiv_ov(dividend, Overflow);
+    EXPECT_TRUE(Overflow);
+  }
+  // int32 test overflow
+  {
+    using IntTy = int32_t;
+    APInt divisor(8 * sizeof(IntTy), std::numeric_limits<IntTy>::lowest(),
+                  true);
+    APInt dividend(8 * sizeof(IntTy), IntTy(-1), true);
+    bool Overflow = false;
+    (void)divisor.sfloordiv_ov(dividend, Overflow);
+    EXPECT_TRUE(Overflow);
+  }
+  // int64 test overflow
+  {
+    using IntTy = int64_t;
+    APInt divisor(8 * sizeof(IntTy), std::numeric_limits<IntTy>::lowest(),
+                  true);
+    APInt dividend(8 * sizeof(IntTy), IntTy(-1), true);
+    bool Overflow = false;
+    (void)divisor.sfloordiv_ov(dividend, Overflow);
+    EXPECT_TRUE(Overflow);
+  }
+  // test all of int8
+  {
+    bool Overflow = false;
+    for (int i = -128; i < 128; ++i) {
+      for (int j = -128; j < 128; ++j) {
+        if (j == 0)
+          continue;
+
+        int8_t a = static_cast<int8_t>(i);
+        int8_t b = static_cast<int8_t>(j);
+
+        APInt divisor(8, a, true);
+        APInt dividend(8, b, true);
+        APInt quotient = divisor.sfloordiv_ov(dividend, Overflow);
+
+        if (i == -128 && j == -1) {
+          EXPECT_TRUE(Overflow);
+          continue;
+        }
+
+        if (((i >= 0 && j > 0) || (i <= 0 && j < 0)) ||
+            (i % j == 0)) // if quotient >= 0 and remain == 0 floordiv
+                          // equivalent to div
+          EXPECT_EQ(quotient.getSExtValue(), a / b);
+        else
+          EXPECT_EQ(quotient.getSExtValue(), a / b - 1);
+        EXPECT_FALSE(Overflow);
+      }
+    }
+  }
+}
+
 TEST(APIntTest, SolveQuadraticEquationWrap) {
   // Verify that "Solution" is the first non-negative integer that solves
   // Ax^2 + Bx + C = "0 or overflow", i.e. that it is a correct solution