Revert "[AggressiveInstCombine] Lower Table Based CTTZ"

This reverts commit fec01ee.

According to asan, this patch introduces a heap use after free.

Author: zygoloid

llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp

@@ -473,168 +473,6 @@ foldSqrt(Instruction &I, TargetTransformInfo &TTI, TargetLibraryInfo &TLI) {
   return false;
 }
 
-// Check if this array of constants represents a cttz table.
-// Iterate over the elements from \p Table by trying to find/match all
-// the numbers from 0 to \p InputBits that should represent cttz results.
-static bool isCTTZTable(const ConstantDataArray &Table, uint64_t Mul,
-                        uint64_t Shift, uint64_t InputBits) {
-  unsigned Length = Table.getNumElements();
-  if (Length < InputBits || Length > InputBits * 2)
-    return false;
-
-  APInt Mask = APInt::getBitsSetFrom(InputBits, Shift);
-  unsigned Matched = 0;
-
-  for (unsigned i = 0; i < Length; i++) {
-    uint64_t Element = Table.getElementAsInteger(i);
-    if (Element >= InputBits)
-      continue;
-
-    // Check if \p Element matches a concrete answer. It could fail for some
-    // elements that are never accessed, so we keep iterating over each element
-    // from the table. The number of matched elements should be equal to the
-    // number of potential right answers which is \p InputBits actually.
-    if ((((Mul << Element) & Mask.getZExtValue()) >> Shift) == i)
-      Matched++;
-  }
-
-  return Matched == InputBits;
-}
-
-// Try to recognize table-based ctz implementation.
-// E.g., an example in C (for more cases please see the llvm/tests):
-// int f(unsigned x) {
-//    static const char table[32] =
-//      {0, 1, 28, 2, 29, 14, 24, 3, 30,
-//       22, 20, 15, 25, 17, 4, 8, 31, 27,
-//       13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9};
-//    return table[((unsigned)((x & -x) * 0x077CB531U)) >> 27];
-// }
-// this can be lowered to `cttz` instruction.
-// There is also a special case when the element is 0.
-//
-// Here are some examples or LLVM IR for a 64-bit target:
-//
-// CASE 1:
-// %sub = sub i32 0, %x
-// %and = and i32 %sub, %x
-// %mul = mul i32 %and, 125613361
-// %shr = lshr i32 %mul, 27
-// %idxprom = zext i32 %shr to i64
-// %arrayidx = getelementptr inbounds [32 x i8], [32 x i8]* @ctz1.table, i64 0,
-// i64 %idxprom %0 = load i8, i8* %arrayidx, align 1, !tbaa !8
-//
-// CASE 2:
-// %sub = sub i32 0, %x
-// %and = and i32 %sub, %x
-// %mul = mul i32 %and, 72416175
-// %shr = lshr i32 %mul, 26
-// %idxprom = zext i32 %shr to i64
-// %arrayidx = getelementptr inbounds [64 x i16], [64 x i16]* @ctz2.table, i64
-// 0, i64 %idxprom %0 = load i16, i16* %arrayidx, align 2, !tbaa !8
-//
-// CASE 3:
-// %sub = sub i32 0, %x
-// %and = and i32 %sub, %x
-// %mul = mul i32 %and, 81224991
-// %shr = lshr i32 %mul, 27
-// %idxprom = zext i32 %shr to i64
-// %arrayidx = getelementptr inbounds [32 x i32], [32 x i32]* @ctz3.table, i64
-// 0, i64 %idxprom %0 = load i32, i32* %arrayidx, align 4, !tbaa !8
-//
-// CASE 4:
-// %sub = sub i64 0, %x
-// %and = and i64 %sub, %x
-// %mul = mul i64 %and, 283881067100198605
-// %shr = lshr i64 %mul, 58
-// %arrayidx = getelementptr inbounds [64 x i8], [64 x i8]* @table, i64 0, i64
-// %shr %0 = load i8, i8* %arrayidx, align 1, !tbaa !8
-//
-// All this can be lowered to @llvm.cttz.i32/64 intrinsic.
-static bool tryToRecognizeTableBasedCttz(Instruction &I) {
-  LoadInst *LI = dyn_cast<LoadInst>(&I);
-  if (!LI)
-    return false;
-
-  Type *AccessType = LI->getType();
-  if (!AccessType->isIntegerTy())
-    return false;
-
-  GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(LI->getPointerOperand());
-  if (!GEP || !GEP->isInBounds() || GEP->getNumIndices() != 2)
-    return false;
-
-  if (!GEP->getSourceElementType()->isArrayTy())
-    return false;
-
-  uint64_t ArraySize = GEP->getSourceElementType()->getArrayNumElements();
-  if (ArraySize != 32 && ArraySize != 64)
-    return false;
-
-  GlobalVariable *GVTable = dyn_cast<GlobalVariable>(GEP->getPointerOperand());
-  if (!GVTable || !GVTable->hasInitializer())
-    return false;
-
-  ConstantDataArray *ConstData =
-      dyn_cast<ConstantDataArray>(GVTable->getInitializer());
-  if (!ConstData)
-    return false;
-
-  if (!match(GEP->idx_begin()->get(), m_ZeroInt()))
-    return false;
-
-  Value *Idx2 = std::next(GEP->idx_begin())->get();
-  Value *X1;
-  uint64_t MulConst, ShiftConst;
-  // FIXME: 64-bit targets have `i64` type for the GEP index, so this match will
-  // probably fail for other (e.g. 32-bit) targets.
-  if (!match(Idx2, m_ZExtOrSelf(
-                       m_LShr(m_Mul(m_c_And(m_Neg(m_Value(X1)), m_Deferred(X1)),
-                                    m_ConstantInt(MulConst)),
-                              m_ConstantInt(ShiftConst)))))
-    return false;
-
-  unsigned InputBits = X1->getType()->getScalarSizeInBits();
-  if (InputBits != 32 && InputBits != 64)
-    return false;
-
-  // Shift should extract top 5..7 bits.
-  if (InputBits - Log2_32(InputBits) != ShiftConst &&
-      InputBits - Log2_32(InputBits) - 1 != ShiftConst)
-    return false;
-
-  if (!isCTTZTable(*ConstData, MulConst, ShiftConst, InputBits))
-    return false;
-
-  auto ZeroTableElem = ConstData->getElementAsInteger(0);
-  bool DefinedForZero = ZeroTableElem == InputBits;
-
-  IRBuilder<> B(LI);
-  ConstantInt *BoolConst = B.getInt1(!DefinedForZero);
-  Type *XType = X1->getType();
-  auto Cttz = B.CreateIntrinsic(Intrinsic::cttz, {XType}, {X1, BoolConst});
-  Value *ZExtOrTrunc = nullptr;
-
-  if (DefinedForZero) {
-    ZExtOrTrunc = B.CreateZExtOrTrunc(Cttz, AccessType);
-  } else {
-    // If the value in elem 0 isn't the same as InputBits, we still want to
-    // produce the value from the table.
-    auto Cmp = B.CreateICmpEQ(X1, ConstantInt::get(XType, 0));
-    auto Select =
-        B.CreateSelect(Cmp, ConstantInt::get(XType, ZeroTableElem), Cttz);
-
-    // NOTE: If the table[0] is 0, but the cttz(0) is defined by the Target
-    // it should be handled as: `cttz(x) & (typeSize - 1)`.
-
-    ZExtOrTrunc = B.CreateZExtOrTrunc(Select, AccessType);
-  }
-
-  LI->replaceAllUsesWith(ZExtOrTrunc);
-
-  return true;
-}
-
 /// This is the entry point for folds that could be implemented in regular
 /// InstCombine, but they are separated because they are not expected to
 /// occur frequently and/or have more than a constant-length pattern match.
@@ -658,7 +496,6 @@ static bool foldUnusualPatterns(Function &F, DominatorTree &DT,
       MadeChange |= tryToRecognizePopCount(I);
       MadeChange |= tryToFPToSat(I, TTI);
       MadeChange |= foldSqrt(I, TTI, TLI);
-      MadeChange |= tryToRecognizeTableBasedCttz(I);
     }
   }