[llvm] df868ed - "Recommit "[AggressiveInstCombine] Lower Table Based CTTZ""

Djordje Todorovic via llvm-commits llvm-commits at lists.llvm.org
Fri Sep 9 01:30:13 PDT 2022


Author: Djordje Todorovic
Date: 2022-09-09T10:29:39+02:00
New Revision: df868edee561eb973edd85ec9df41c67aa0bff6b

URL: https://github.com/llvm/llvm-project/commit/df868edee561eb973edd85ec9df41c67aa0bff6b
DIFF: https://github.com/llvm/llvm-project/commit/df868edee561eb973edd85ec9df41c67aa0bff6b.diff

LOG: "Recommit "[AggressiveInstCombine] Lower Table Based CTTZ""

This reverts commit 053841c5624ca7eacd108a26071d8a1cefe1bebd.

We faced a use-after-free after pushing the D113291, since the
foldSqrt() has a call to eraseFromParent(). The function
should be at the end of the main loop that folds the patterns.
This patch fixes that.

Added: 
    llvm/test/Transforms/AggressiveInstCombine/lower-table-based-cttz-basics.ll
    llvm/test/Transforms/AggressiveInstCombine/lower-table-based-cttz-dereferencing-pointer.ll
    llvm/test/Transforms/AggressiveInstCombine/lower-table-based-cttz-non-argument-value.ll
    llvm/test/Transforms/AggressiveInstCombine/lower-table-based-cttz-zero-element.ll
    llvm/test/Transforms/AggressiveInstCombine/negative-lower-table-based-cttz.ll
    llvm/test/Transforms/PhaseOrdering/lower-table-based-cttz.ll

Modified: 
    llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp b/llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp
index c3541b5ec58a6..2f01b1d7f7141 100644
--- a/llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp
+++ b/llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp
@@ -473,6 +473,168 @@ 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.
@@ -495,6 +657,10 @@ static bool foldUnusualPatterns(Function &F, DominatorTree &DT,
       MadeChange |= foldGuardedFunnelShift(I, DT);
       MadeChange |= tryToRecognizePopCount(I);
       MadeChange |= tryToFPToSat(I, TTI);
+      MadeChange |= tryToRecognizeTableBasedCttz(I);
+      // NOTE: This function introduces erasing of the instruction `I`, so it
+      // needs to be called at the end of this sequence, otherwise we may make
+      // bugs.
       MadeChange |= foldSqrt(I, TTI, TLI);
     }
   }

diff  --git a/llvm/test/Transforms/AggressiveInstCombine/lower-table-based-cttz-basics.ll b/llvm/test/Transforms/AggressiveInstCombine/lower-table-based-cttz-basics.ll
new file mode 100644
index 0000000000000..bb812010c9afd
--- /dev/null
+++ b/llvm/test/Transforms/AggressiveInstCombine/lower-table-based-cttz-basics.ll
@@ -0,0 +1,257 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -aggressive-instcombine -S < %s | FileCheck %s
+
+;; These cases test lowering of various implementations of table-based ctz
+;; algorithms to the llvm.cttz instruction.
+
+;; C reproducers:
+;; int ctz1 (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];
+;; }
+
+;; int ctz2(unsigned x)
+;; {
+;; #define u 0
+;;  static short table[64] =
+;;   {
+;;     32, 0, 1, 12, 2, 6, u, 13, 3, u, 7, u, u, u, u, 14,
+;;     10, 4, u, u, 8, u, u, 25, u, u, u, u, u, 21, 27, 15,
+;;     31, 11, 5, u, u, u, u, u, 9, u, u, 24, u, u, 20, 26,
+;;     30, u, u, u, u, 23, u, 19, 29, u, 22, 18, 28, 17, 16, u
+;;   };
+;; x = (x & -x) * 0x0450FBAF;
+;; return table[x >> 26];
+;; }
+
+;; int ctz3(unsigned x)
+;;{
+;; static int table[32] =
+;;   {
+;;     0, 1, 2, 24, 3, 19, 6, 25, 22, 4, 20, 10, 16, 7, 12, 26,
+;;      31, 23, 18, 5, 21, 9, 15, 11, 30, 17, 8, 14, 29, 13, 28, 27
+;;    };
+;;  if (x == 0) return 32;
+;;  x = (x & -x) * 0x04D7651F;
+;;  return table[x >> 27];
+;; }
+
+;; static const unsigned long long magic = 0x03f08c5392f756cdULL;
+;;
+;; static const int table[64] = {
+;;     0,  1, 12,  2, 13, 22, 17,  3, 14, 33, 23, 36, 18, 58, 28, 4,
+;;    62, 15, 34, 26, 24, 48, 50, 37, 19, 55, 59, 52, 29, 44, 39,  5,
+;;    63, 11, 21, 16, 32, 35, 57, 27, 61, 25, 47, 49, 54, 51, 43, 38,
+;;    10, 20, 31, 56, 60, 46, 53, 42, 9, 30, 45, 41,  8, 40,  7,  6,
+;; };
+;;
+;; int ctz4 (unsigned long long b)
+;; {
+;;    unsigned long long lsb = b & -b;
+;;    return table[(lsb * magic) >> 58];
+;; }
+;;
+;; int ctz5(unsigned x)
+;; {
+;;  static char table[32] =
+;;    {
+;;      0, 1, 2, 24, 3, 19, 6, 25, 22, 4, 20, 10, 16, 7, 12, 26,
+;;      31, 23, 18, 5, 21, 9, 15, 11, 30, 17, 8, 14, 29, 13, 28, 27
+;;    };
+;;  x = (x & -x)*0x04D7651F;
+;;  return table[x >> 27];
+;; }
+
+;; int indexes[] = {
+;;     63, 0, 58, 1, 59, 47, 53, 2,60, 39, 48, 27, 54, 33, 42, 3,
+;;     61, 51, 37, 40, 49, 18, 28, 20, 55, 30, 34, 11, 43, 14, 22, 4,
+;;     62, 57, 46, 52, 38, 26, 32, 41, 50, 36, 17, 19, 29, 10, 13, 21,
+;;     56, 45, 25, 31, 35, 16, 9, 12, 44, 24, 15, 8, 23, 7, 6, 5
+;; };
+;;
+;; int ctz6(unsigned long n)
+;; {
+;;       return indexes[((n & (~n + 1)) * 0x07EDD5E59A4E28C2ull) >> 58];
+;; }
+;;
+;; int ctz8(unsigned v)
+;; {
+;; static const int table[] =
+;; {
+;;  31 ,0 ,1 ,23 ,2 ,18 ,5 ,24 ,21 ,3 ,19 ,9 ,15 ,6 ,11 ,25 ,30 ,22 ,17 ,4 ,20 ;,8 ,14 ,10 ,29 ,16 ,7 ,13 ,28 ,12 ,27 ,26
+;; };
+;; unsigned x =(-v & v);
+;; return table[(unsigned)(x * 0x9AECA3EU) >> 27];
+;; }
+
+ at ctz7.table = internal unnamed_addr constant [32 x i8] c"\00\01\1C\02\1D\0E\18\03\1E\16\14\0F\19\11\04\08\1F\1B\0D\17\15\13\10\07\1A\0C\12\06\0B\05\0A\09", align 1
+
+define i32 @ctz1(i32 %x) {
+; CHECK-LABEL: @ctz1(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @llvm.cttz.i32(i32 [[X:%.*]], i1 true)
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i32 [[X]], 0
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i32 0, i32 [[TMP0]]
+; CHECK-NEXT:    [[TMP3:%.*]] = trunc i32 [[TMP2]] to i8
+; CHECK-NEXT:    [[CONV:%.*]] = zext i8 [[TMP3]] to i32
+; CHECK-NEXT:    ret i32 [[CONV]]
+;
+entry:
+  %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]* @ctz7.table, i64 0, i64 %idxprom
+  %0 = load i8, i8* %arrayidx, align 1
+  %conv = zext i8 %0 to i32
+  ret i32 %conv
+}
+
+ at ctz2.table = internal unnamed_addr constant [64 x i16] [i16 32, i16 0, i16 1, i16 12, i16 2, i16 6, i16 0, i16 13, i16 3, i16 0, i16 7, i16 0, i16 0, i16 0, i16 0, i16 14, i16 10, i16 4, i16 0, i16 0, i16 8, i16 0, i16 0, i16 25, i16 0, i16 0, i16 0, i16 0, i16 0, i16 21, i16 27, i16 15, i16 31, i16 11, i16 5, i16 0, i16 0, i16 0, i16 0, i16 0, i16 9, i16 0, i16 0, i16 24, i16 0, i16 0, i16 20, i16 26, i16 30, i16 0, i16 0, i16 0, i16 0, i16 23, i16 0, i16 19, i16 29, i16 0, i16 22, i16 18, i16 28, i16 17, i16 16, i16 0], align 2
+
+define i32 @ctz2(i32 %x) {
+; CHECK-LABEL: @ctz2(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @llvm.cttz.i32(i32 [[X:%.*]], i1 false)
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc i32 [[TMP0]] to i16
+; CHECK-NEXT:    [[CONV:%.*]] = sext i16 [[TMP1]] to i32
+; CHECK-NEXT:    ret i32 [[CONV]]
+;
+entry:
+  %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
+  %conv = sext i16 %0 to i32
+  ret i32 %conv
+}
+
+ at ctz3.table = internal unnamed_addr constant [32 x i32] [i32 0, i32 1, i32 2, i32 24, i32 3, i32 19, i32 6, i32 25, i32 22, i32 4, i32 20, i32 10, i32 16, i32 7, i32 12, i32 26, i32 31, i32 23, i32 18, i32 5, i32 21, i32 9, i32 15, i32 11, i32 30, i32 17, i32 8, i32 14, i32 29, i32 13, i32 28, i32 27], align 4
+
+define i32 @ctz3(i32 %x) {
+; CHECK-LABEL: @ctz3(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[X:%.*]], 0
+; CHECK-NEXT:    br i1 [[CMP]], label [[RETURN:%.*]], label [[IF_END:%.*]]
+; CHECK:       if.end:
+; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @llvm.cttz.i32(i32 [[X]], i1 true)
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i32 [[X]], 0
+; CHECK-NEXT:    br label [[RETURN]]
+; CHECK:       return:
+; CHECK-NEXT:    [[RETVAL_0:%.*]] = phi i32 [ [[TMP0]], [[IF_END]] ], [ 32, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    ret i32 [[RETVAL_0]]
+;
+entry:
+  %cmp = icmp eq i32 %x, 0
+  br i1 %cmp, label %return, label %if.end
+
+if.end:                                           ; preds = %entry
+  %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
+  br label %return
+
+return:                                           ; preds = %entry, %if.end
+  %retval.0 = phi i32 [ %0, %if.end ], [ 32, %entry ]
+  ret i32 %retval.0
+}
+
+ at table = internal unnamed_addr constant [64 x i32] [i32 0, i32 1, i32 12, i32 2, i32 13, i32 22, i32 17, i32 3, i32 14, i32 33, i32 23, i32 36, i32 18, i32 58, i32 28, i32 4, i32 62, i32 15, i32 34, i32 26, i32 24, i32 48, i32 50, i32 37, i32 19, i32 55, i32 59, i32 52, i32 29, i32 44, i32 39, i32 5, i32 63, i32 11, i32 21, i32 16, i32 32, i32 35, i32 57, i32 27, i32 61, i32 25, i32 47, i32 49, i32 54, i32 51, i32 43, i32 38, i32 10, i32 20, i32 31, i32 56, i32 60, i32 46, i32 53, i32 42, i32 9, i32 30, i32 45, i32 41, i32 8, i32 40, i32 7, i32 6], align 4
+
+define i32 @ctz4(i64 %b) {
+; CHECK-LABEL: @ctz4(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = call i64 @llvm.cttz.i64(i64 [[B:%.*]], i1 true)
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i64 [[B]], 0
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i64 0, i64 [[TMP0]]
+; CHECK-NEXT:    [[TMP3:%.*]] = trunc i64 [[TMP2]] to i32
+; CHECK-NEXT:    ret i32 [[TMP3]]
+;
+entry:
+  %sub = sub i64 0, %b
+  %and = and i64 %sub, %b
+  %mul = mul i64 %and, 283881067100198605
+  %shr = lshr i64 %mul, 58
+  %arrayidx = getelementptr inbounds [64 x i32], [64 x i32]* @table, i64 0, i64 %shr
+  %0 = load i32, i32* %arrayidx, align 4
+  ret i32 %0
+}
+
+ at ctz5.table = internal unnamed_addr constant [32 x i8] c"\00\01\02\18\03\13\06\19\16\04\14\0A\10\07\0C\1A\1F\17\12\05\15\09\0F\0B\1E\11\08\0E\1D\0D\1C\1B", align 1
+
+define i32 @ctz5(i32 %x) {
+; CHECK-LABEL: @ctz5(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @llvm.cttz.i32(i32 [[X:%.*]], i1 true)
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i32 [[X]], 0
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i32 0, i32 [[TMP0]]
+; CHECK-NEXT:    [[TMP3:%.*]] = trunc i32 [[TMP2]] to i8
+; CHECK-NEXT:    [[CONV:%.*]] = zext i8 [[TMP3]] to i32
+; CHECK-NEXT:    ret i32 [[CONV]]
+;
+entry:
+  %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 i8], [32 x i8]* @ctz5.table, i64 0, i64 %idxprom
+  %0 = load i8, i8* %arrayidx, align 1
+  %conv = zext i8 %0 to i32
+  ret i32 %conv
+}
+
+ at ctz6.table = global [64 x i32] [i32 63, i32 0, i32 58, i32 1, i32 59, i32 47, i32 53, i32 2, i32 60, i32 39, i32 48, i32 27, i32 54, i32 33, i32 42, i32 3, i32 61, i32 51, i32 37, i32 40, i32 49, i32 18, i32 28, i32 20, i32 55, i32 30, i32 34, i32 11, i32 43, i32 14, i32 22, i32 4, i32 62, i32 57, i32 46, i32 52, i32 38, i32 26, i32 32, i32 41, i32 50, i32 36, i32 17, i32 19, i32 29, i32 10, i32 13, i32 21, i32 56, i32 45, i32 25, i32 31, i32 35, i32 16, i32 9, i32 12, i32 44, i32 24, i32 15, i32 8, i32 23, i32 7, i32 6, i32 5], align 4
+
+define i32 @ctz6(i64 %n) {
+; CHECK-LABEL: @ctz6(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = call i64 @llvm.cttz.i64(i64 [[N:%.*]], i1 true)
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i64 [[N]], 0
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i64 63, i64 [[TMP0]]
+; CHECK-NEXT:    [[TMP3:%.*]] = trunc i64 [[TMP2]] to i32
+; CHECK-NEXT:    ret i32 [[TMP3]]
+;
+entry:
+  %add = sub i64 0, %n
+  %and = and i64 %add, %n
+  %mul = mul i64 %and, 571347909858961602
+  %shr = lshr i64 %mul, 58
+  %arrayidx = getelementptr inbounds [64 x i32], [64 x i32]* @ctz6.table, i64 0, i64 %shr
+  %0 = load i32, i32* %arrayidx, align 4
+  ret i32 %0
+}
+
+ at ctz8.table = internal unnamed_addr constant [32 x i32] [i32 31, i32 0, i32 1, i32 23, i32 2, i32 18, i32 5, i32 24, i32 21, i32 3, i32 19, i32 9, i32 15, i32 6, i32 11, i32 25, i32 30, i32 22, i32 17, i32 4, i32 20, i32 8, i32 14, i32 10, i32 29, i32 16, i32 7, i32 13, i32 28, i32 12, i32 27, i32 26], align 4
+
+define i32 @ctz8(i32 %v) {
+; CHECK-LABEL: @ctz8(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @llvm.cttz.i32(i32 [[V:%.*]], i1 true)
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i32 [[V]], 0
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i32 31, i32 [[TMP0]]
+; CHECK-NEXT:    ret i32 [[TMP2]]
+;
+entry:
+  %sub = sub i32 0, %v
+  %and = and i32 %sub, %v
+  %mul = mul i32 %and, 162449982
+  %shr = lshr i32 %mul, 27
+  %idxprom = zext i32 %shr to i64
+  %arrayidx = getelementptr inbounds [32 x i32], [32 x i32]* @ctz8.table, i64 0, i64 %idxprom
+  %0 = load i32, i32* %arrayidx, align 4
+  ret i32 %0
+}

diff  --git a/llvm/test/Transforms/AggressiveInstCombine/lower-table-based-cttz-dereferencing-pointer.ll b/llvm/test/Transforms/AggressiveInstCombine/lower-table-based-cttz-dereferencing-pointer.ll
new file mode 100644
index 0000000000000..0bd4e2c2862b6
--- /dev/null
+++ b/llvm/test/Transforms/AggressiveInstCombine/lower-table-based-cttz-dereferencing-pointer.ll
@@ -0,0 +1,42 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -aggressive-instcombine -S < %s | FileCheck %s
+
+;; static const unsigned long long magic = 0x03f08c5392f756cdULL;
+;;
+;; static const int table[64] = {
+;;     0,  1, 12,  2, 13, 22, 17,  3,
+;;   14, 33, 23, 36, 18, 58, 28,  4,
+;;    62, 15, 34, 26, 24, 48, 50, 37,
+;;    19, 55, 59, 52, 29, 44, 39,  5,
+;;    63, 11, 21, 16, 32, 35, 57, 27,
+;;    61, 25, 47, 49, 54, 51, 43, 38,
+;;    10, 20, 31, 56, 60, 46, 53, 42,
+;;     9, 30, 45, 41,  8, 40,  7,  6,
+;; };
+;;
+;; int ctz6 (unsigned long long * const b) {
+;;    return table[(((*b) & -(*b)) * magic) >> 58];
+;; }
+
+ at table = internal unnamed_addr constant [64 x i32] [i32 0, i32 1, i32 12, i32 2, i32 13, i32 22, i32 17, i32 3, i32 14, i32 33, i32 23, i32 36, i32 18, i32 58, i32 28, i32 4, i32 62, i32 15, i32 34, i32 26, i32 24, i32 48, i32 50, i32 37, i32 19, i32 55, i32 59, i32 52, i32 29, i32 44, i32 39, i32 5, i32 63, i32 11, i32 21, i32 16, i32 32, i32 35, i32 57, i32 27, i32 61, i32 25, i32 47, i32 49, i32 54, i32 51, i32 43, i32 38, i32 10, i32 20, i32 31, i32 56, i32 60, i32 46, i32 53, i32 42, i32 9, i32 30, i32 45, i32 41, i32 8, i32 40, i32 7, i32 6], align 4
+
+define i32 @ctz6(i64* nocapture readonly %b) {
+; CHECK-LABEL: @ctz6(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = load i64, i64* [[B:%.*]], align 8
+; CHECK-NEXT:    [[TMP1:%.*]] = call i64 @llvm.cttz.i64(i64 [[TMP0]], i1 true)
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp eq i64 [[TMP0]], 0
+; CHECK-NEXT:    [[TMP3:%.*]] = select i1 [[TMP2]], i64 0, i64 [[TMP1]]
+; CHECK-NEXT:    [[TMP4:%.*]] = trunc i64 [[TMP3]] to i32
+; CHECK-NEXT:    ret i32 [[TMP4]]
+;
+entry:
+  %0 = load i64, i64* %b, align 8
+  %sub = sub i64 0, %0
+  %and = and i64 %0, %sub
+  %mul = mul i64 %and, 283881067100198605
+  %shr = lshr i64 %mul, 58
+  %arrayidx = getelementptr inbounds [64 x i32], [64 x i32]* @table, i64 0, i64 %shr
+  %1 = load i32, i32* %arrayidx, align 4
+  ret i32 %1
+}

diff  --git a/llvm/test/Transforms/AggressiveInstCombine/lower-table-based-cttz-non-argument-value.ll b/llvm/test/Transforms/AggressiveInstCombine/lower-table-based-cttz-non-argument-value.ll
new file mode 100644
index 0000000000000..c034f88ff37df
--- /dev/null
+++ b/llvm/test/Transforms/AggressiveInstCombine/lower-table-based-cttz-non-argument-value.ll
@@ -0,0 +1,45 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -aggressive-instcombine -S < %s | FileCheck %s
+
+;; C reproducers:
+;; #include "stdio.h"
+;; unsigned x;
+;;
+;; int test ()
+;; {
+;;  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];
+;; }
+;;
+
+ at x = global i32 0, align 4
+ at .str = private constant [3 x i8] c"%u\00", align 1
+ at test.table = internal constant [32 x i8] c"\00\01\1C\02\1D\0E\18\03\1E\16\14\0F\19\11\04\08\1F\1B\0D\17\15\13\10\07\1A\0C\12\06\0B\05\0A\09", align 1
+
+define i32 @test() {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = load i32, i32* @x, align 4
+; CHECK-NEXT:    [[TMP1:%.*]] = call i32 @llvm.cttz.i32(i32 [[TMP0]], i1 true)
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp eq i32 [[TMP0]], 0
+; CHECK-NEXT:    [[TMP3:%.*]] = select i1 [[TMP2]], i32 0, i32 [[TMP1]]
+; CHECK-NEXT:    [[TMP4:%.*]] = trunc i32 [[TMP3]] to i8
+; CHECK-NEXT:    [[CONV:%.*]] = zext i8 [[TMP4]] to i32
+; CHECK-NEXT:    ret i32 [[CONV]]
+;
+entry:
+  %0 = load i32, i32* @x, align 4
+  %sub = sub i32 0, %0
+  %and = and i32 %0, %sub
+  %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]* @test.table, i64 0, i64 %idxprom
+  %1 = load i8, i8* %arrayidx, align 1
+  %conv = zext i8 %1 to i32
+  ret i32 %conv
+}

diff  --git a/llvm/test/Transforms/AggressiveInstCombine/lower-table-based-cttz-zero-element.ll b/llvm/test/Transforms/AggressiveInstCombine/lower-table-based-cttz-zero-element.ll
new file mode 100644
index 0000000000000..c744226e2651c
--- /dev/null
+++ b/llvm/test/Transforms/AggressiveInstCombine/lower-table-based-cttz-zero-element.ll
@@ -0,0 +1,26 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -aggressive-instcombine -S < %s | FileCheck %s
+
+ at ctz1.table = internal constant [32 x i8] c"\00\01\1C\02\1D\0E\18\03\1E\16\14\0F\19\11\04\08\1F\1B\0D\17\15\13\10\07\1A\0C\12\06\0B\05\0A\09", align 1
+
+define i32 @ctz1(i32 %x) {
+; CHECK-LABEL: @ctz1(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @llvm.cttz.i32(i32 [[X:%.*]], i1 true)
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i32 [[X]], 0
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i32 0, i32 [[TMP0]]
+; CHECK-NEXT:    [[TMP3:%.*]] = trunc i32 [[TMP2]] to i8
+; CHECK-NEXT:    [[CONV:%.*]] = zext i8 [[TMP3]] to i32
+; CHECK-NEXT:    ret i32 [[CONV]]
+;
+entry:
+  %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
+  %conv = zext i8 %0 to i32
+  ret i32 %conv
+}

diff  --git a/llvm/test/Transforms/AggressiveInstCombine/negative-lower-table-based-cttz.ll b/llvm/test/Transforms/AggressiveInstCombine/negative-lower-table-based-cttz.ll
new file mode 100644
index 0000000000000..67c79111e3626
--- /dev/null
+++ b/llvm/test/Transforms/AggressiveInstCombine/negative-lower-table-based-cttz.ll
@@ -0,0 +1,112 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -aggressive-instcombine -S < %s | FileCheck %s --implicit-check-not=llvm.cttz
+
+;; These cases should ensure we are not lowering of some wrong implementations
+;; of table-based ctz algorithms to the llvm.cttz instruction.
+
+ at ctz7.table = internal unnamed_addr constant [32 x i8] c"\05\01\1C\02\1D\0E\18\03\1E\16\14\0F\19\11\04\08\1F\1B\0D\17\15\13\10\07\1A\0C\12\06\0B\05\0A\09", align 1
+
+;; This is a negative test with a wrong table constant.
+
+define i32 @ctz1(i32 %x) {
+entry:
+  %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]* @ctz7.table, i64 0, i64 %idxprom
+  %0 = load i8, i8* %arrayidx, align 1
+  %conv = zext i8 %0 to i32
+  ret i32 %conv
+}
+
+;; These are some negative tests with a wrong instruction sequences.
+
+ at ctz1.table = internal unnamed_addr constant [32 x i8] c"\00\01\1C\02\1D\0E\18\03\1E\16\14\0F\19\11\04\08\1F\1B\0D\17\15\13\10\07\1A\0C\12\06\0B\05\0A\09", align 1
+
+define i32 @ctz2(i32 %x) {
+entry:
+  %sub = sub i32 1, %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
+  %conv = zext i8 %0 to i32
+  ret i32 %conv
+}
+
+define i32 @ctz3(i32 %x) {
+entry:
+  %sub = sub i32 0, %x
+  %and = and i32 %sub, %x
+  %mul = mul i32 %and, 125613362
+  %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
+  %conv = zext i8 %0 to i32
+  ret i32 %conv
+}
+
+define i32 @ctz4(i32 %x) {
+entry:
+  %sub = sub i32 0, %x
+  %and = and i32 %sub, %x
+  %mul = mul i32 %and, 125613361
+  %shr = lshr i32 %mul, 26
+  %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
+  %conv = zext i8 %0 to i32
+  ret i32 %conv
+}
+
+;; This is a negative test with a wrong table size and constants.
+
+ at ctz3.table = internal unnamed_addr constant [128 x i8] c"\00\01\1C\02\1D\0E\18\03\1E\16\14\0F\19\11\04\08\1F\1B\0D\17\15\13\10\07\1A\0C\12\06\0B\05\0A\09\00\01\1C\02\1D\0E\18\03\1E\16\14\0F\19\11\04\08\1F\1B\0D\17\15\13\10\07\1A\0C\12\06\0B\05\0A\09\00\01\1C\02\1D\0E\18\03\1E\16\14\0F\19\11\04\08\1F\1B\0D\17\15\13\10\07\1A\0C\12\06\0B\05\0A\09\00\01\1C\02\1D\0E\18\03\1E\16\14\0F\19\11\04\08\1F\1B\0D\17\15\13\10\07\1A\0C\12\06\0B\05\0A\09", align 1
+
+define i32 @ctz5(i32 %x) {
+entry:
+  %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 [128 x i8], [128 x i8]* @ctz3.table, i64 0, i64 %idxprom
+  %0 = load i8, i8* %arrayidx, align 1
+  %conv = zext i8 %0 to i32
+  ret i32 %conv
+}
+
+;; A test with an extern global variable representing the table.
+;; extern int table[32];
+;;
+;;  int ctz6(unsigned x) {
+;;    if (x == 0) return 32;
+;;    x = (x & -x) * 0x04D7651F;
+;;    return table[x >> 27];
+;;  }
+
+ at table = external global [32 x i32], align 16
+define i32 @ctz6(i32 noundef %x) {
+entry:
+  %cmp = icmp eq i32 %x, 0
+  br i1 %cmp, label %return, label %if.end
+
+if.end:                                           ; preds = %entry
+  %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]* @table, i64 0, i64 %idxprom
+  %0 = load i32, i32* %arrayidx, align 4
+  br label %return
+
+return:                                           ; preds = %entry, %if.end
+  %retval.0 = phi i32 [ %0, %if.end ], [ 32, %entry ]
+  ret i32 %retval.0
+}

diff  --git a/llvm/test/Transforms/PhaseOrdering/lower-table-based-cttz.ll b/llvm/test/Transforms/PhaseOrdering/lower-table-based-cttz.ll
new file mode 100644
index 0000000000000..284873a973762
--- /dev/null
+++ b/llvm/test/Transforms/PhaseOrdering/lower-table-based-cttz.ll
@@ -0,0 +1,37 @@
+;; This tests lowering of the implementations of table-based ctz
+;; algorithm to the llvm.cttz instruction in the -O3 case.
+
+;; C producer:
+;; int ctz1 (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];
+;; }
+;; Compiled as: clang -O3 test.c -S -emit-llvm -Xclang -disable-llvm-optzns
+
+; RUN: opt -O3 -S < %s | FileCheck %s
+
+; CHECK: call i32 @llvm.cttz.i32
+
+ at ctz1.table = internal constant [32 x i8] c"\00\01\1C\02\1D\0E\18\03\1E\16\14\0F\19\11\04\08\1F\1B\0D\17\15\13\10\07\1A\0C\12\06\0B\05\0A\09", align 16
+
+define i32 @ctz1(i32 noundef %x) {
+entry:
+  %x.addr = alloca i32, align 4
+  store i32 %x, ptr %x.addr, align 4
+  %0 = load i32, ptr %x.addr, align 4
+  %1 = load i32, ptr %x.addr, align 4
+  %sub = sub i32 0, %1
+  %and = and i32 %0, %sub
+  %mul = mul i32 %and, 125613361
+  %shr = lshr i32 %mul, 27
+  %idxprom = zext i32 %shr to i64
+  %arrayidx = getelementptr inbounds [32 x i8], ptr @ctz1.table, i64 0, i64 %idxprom
+  %2 = load i8, ptr %arrayidx, align 1
+  %conv = sext i8 %2 to i32
+  ret i32 %conv
+}


        


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