[llvm] [LoopIdiomRecognizer] Implement CRC recognition (PR #79295)

[Craig Topper via llvm-commits]

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@@ -2868,3 +2889,888 @@ bool LoopIdiomRecognize::recognizeShiftUntilZero() {
   ++NumShiftUntilZero;
   return MadeChange;
 }
+
+static uint64_t reverseBits(uint64_t Num, unsigned NumBits) {
+  uint64_t Reversed = 0;
+  for (unsigned i = 1; i <= NumBits; i++) {
+    Reversed |= (Num & 1) << (NumBits - i);
+    Num >>= 1;
+  }
+  return Reversed;
+}
+
+class ValueBits {
+  // This is a representation of a value's bits in terms of references to
+  // other values' bits, or 1/0 if the bit is known. This allows symbolic
+  // execution of bitwise instructions without knowing the exact values.
+  //
+  // Example:
+  //
+  // LLVM IR Value i8 %x:
+  // [%x[7], %x[6], %x[5], %x[4], %x[3], %x[2], %x[1], %x[0]]
+  //
+  // %shr = lshr i8 %x, 2
+  // [ 0, 0, %x[7], %x[6], %x[5], %x[4], %x[3], %x[2]]
+  //
+  // %shl = shl i8 %shr, 1
+  // [ 0, %x[7], %x[6], %x[5], %x[4], %x[3], %x[2], 0]
+  //
+  // %xor = xor i8 %shl, 0xb
+  // [ 0, %x[7], %x[6], %x[5], %x[4]^1, %x[3], %x[2]^1, 1]
+public:
+  class ValueBit {
+  public:
+    enum BitType { ONE, ZERO, REF, XOR };
+
+  private:
+    BitType _Type;
+    std::pair<Value *, uint64_t> _BitRef;
+    ValueBit *_LHS;
+    ValueBit *_RHS;
+
+    ValueBit(BitType Type) : _Type(Type) {}
+    ValueBit(BitType Type, std::pair<Value *, uint64_t> BitRef)
+        : _Type(Type), _BitRef(BitRef) {}
+    ValueBit(BitType Type, ValueBit *LHS, ValueBit *RHS)
+        : _Type(Type), _LHS(LHS), _RHS(RHS) {}
+
+  public:
+    static ValueBit *CreateOneBit() { return new ValueBit(BitType::ONE); }
+    static ValueBit *CreateZeroBit() { return new ValueBit(BitType::ZERO); }
+    static ValueBit *CreateRefBit(Value *Ref, uint64_t Offset) {
+      return new ValueBit(BitType::REF, std::make_pair(Ref, Offset));
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topperc wrote:

Is this memory ever freed? A quick search doesn't show any calls to `delete` or `unique_ptr`

https://github.com/llvm/llvm-project/pull/79295