[CmpInstAnalysis] Decompose icmp eq (and x, C) C2 (llvm#136367)

This type of decomposition is used in multiple places already. Adding it
to `CmpInstAnalysis` reduces code duplication.

Author: jrbyrnes

llvm/include/llvm/Analysis/CmpInstAnalysis.h

@@ -102,17 +102,21 @@ namespace llvm {
   };
 
   /// Decompose an icmp into the form ((X & Mask) pred C) if possible.
-  /// Unless \p AllowNonZeroC is true, C will always be 0.
+  /// Unless \p AllowNonZeroC is true, C will always be 0. If \p
+  /// DecomposeAnd is specified, then, for equality predicates, this will
+  /// decompose bitmasking via `and`.
   std::optional<DecomposedBitTest>
   decomposeBitTestICmp(Value *LHS, Value *RHS, CmpInst::Predicate Pred,
-                       bool LookThroughTrunc = true,
-                       bool AllowNonZeroC = false);
+                       bool LookThroughTrunc = true, bool AllowNonZeroC = false,
+                       bool DecomposeAnd = false);
 
   /// Decompose an icmp into the form ((X & Mask) pred C) if
   /// possible. Unless \p AllowNonZeroC is true, C will always be 0.
+  /// If \p DecomposeAnd is specified, then, for equality predicates, this
+  /// will decompose bitmasking via `and`.
   std::optional<DecomposedBitTest>
   decomposeBitTest(Value *Cond, bool LookThroughTrunc = true,
-                   bool AllowNonZeroC = false);
+                   bool AllowNonZeroC = false, bool DecomposeAnd = false);
 
 } // end namespace llvm
 

llvm/lib/Analysis/CmpInstAnalysis.cpp

@@ -75,11 +75,13 @@ Constant *llvm::getPredForFCmpCode(unsigned Code, Type *OpTy,
 
 std::optional<DecomposedBitTest>
 llvm::decomposeBitTestICmp(Value *LHS, Value *RHS, CmpInst::Predicate Pred,
-                           bool LookThruTrunc, bool AllowNonZeroC) {
+                           bool LookThruTrunc, bool AllowNonZeroC,
+                           bool DecomposeAnd) {
   using namespace PatternMatch;
 
   const APInt *OrigC;
-  if (!ICmpInst::isRelational(Pred) || !match(RHS, m_APIntAllowPoison(OrigC)))
+  if ((ICmpInst::isEquality(Pred) && !DecomposeAnd) ||
+      !match(RHS, m_APIntAllowPoison(OrigC)))
     return std::nullopt;
 
   bool Inverted = false;
@@ -128,7 +130,7 @@ llvm::decomposeBitTestICmp(Value *LHS, Value *RHS, CmpInst::Predicate Pred,
 
     return std::nullopt;
   }
-  case ICmpInst::ICMP_ULT:
+  case ICmpInst::ICMP_ULT: {
     // X <u 2^n is equivalent to (X & ~(2^n-1)) == 0.
     if (C.isPowerOf2()) {
       Result.Mask = -C;
@@ -147,6 +149,22 @@ llvm::decomposeBitTestICmp(Value *LHS, Value *RHS, CmpInst::Predicate Pred,
 
     return std::nullopt;
   }
+  case ICmpInst::ICMP_EQ:
+  case ICmpInst::ICMP_NE: {
+    assert(DecomposeAnd);
+    const APInt *AndC;
+    Value *AndVal;
+    if (match(LHS, m_And(m_Value(AndVal), m_APIntAllowPoison(AndC)))) {
+      LHS = AndVal;
+      Result.Mask = *AndC;
+      Result.C = C;
+      Result.Pred = Pred;
+      break;
+    }
+
+    return std::nullopt;
+  }
+  }
 
   if (!AllowNonZeroC && !Result.C.isZero())
     return std::nullopt;
@@ -166,16 +184,18 @@ llvm::decomposeBitTestICmp(Value *LHS, Value *RHS, CmpInst::Predicate Pred,
   return Result;
 }
 
-std::optional<DecomposedBitTest>
-llvm::decomposeBitTest(Value *Cond, bool LookThruTrunc, bool AllowNonZeroC) {
+std::optional<DecomposedBitTest> llvm::decomposeBitTest(Value *Cond,
+                                                        bool LookThruTrunc,
+                                                        bool AllowNonZeroC,
+                                                        bool DecomposeAnd) {
   using namespace PatternMatch;
   if (auto *ICmp = dyn_cast<ICmpInst>(Cond)) {
     // Don't allow pointers. Splat vectors are fine.
     if (!ICmp->getOperand(0)->getType()->isIntOrIntVectorTy())
       return std::nullopt;
     return decomposeBitTestICmp(ICmp->getOperand(0), ICmp->getOperand(1),
                                 ICmp->getPredicate(), LookThruTrunc,
-                                AllowNonZeroC);
+                                AllowNonZeroC, DecomposeAnd);
   }
   Value *X;
   if (Cond->getType()->isIntOrIntVectorTy(1) &&

llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

@@ -875,22 +875,16 @@ static Value *foldSignedTruncationCheck(ICmpInst *ICmp0, ICmpInst *ICmp1,
                            APInt &UnsetBitsMask) -> bool {
     CmpPredicate Pred = ICmp->getPredicate();
     // Can it be decomposed into  icmp eq (X & Mask), 0  ?
-    auto Res =
-        llvm::decomposeBitTestICmp(ICmp->getOperand(0), ICmp->getOperand(1),
-                                   Pred, /*LookThroughTrunc=*/false);
+    auto Res = llvm::decomposeBitTestICmp(
+        ICmp->getOperand(0), ICmp->getOperand(1), Pred,
+        /*LookThroughTrunc=*/false, /*AllowNonZeroC=*/false,
+        /*DecomposeAnd=*/true);
     if (Res && Res->Pred == ICmpInst::ICMP_EQ) {
       X = Res->X;
       UnsetBitsMask = Res->Mask;
       return true;
     }
 
-    // Is it  icmp eq (X & Mask), 0  already?
-    const APInt *Mask;
-    if (match(ICmp, m_ICmp(Pred, m_And(m_Value(X), m_APInt(Mask)), m_Zero())) &&
-        Pred == ICmpInst::ICMP_EQ) {
-      UnsetBitsMask = *Mask;
-      return true;
-    }
     return false;
   };
 

llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp

@@ -2761,14 +2761,11 @@ static bool detectShiftUntilBitTestIdiom(Loop *CurLoop, Value *&BaseX,
                              m_LoopInvariant(m_Shl(m_One(), m_Value(BitPos)),
                                              CurLoop))));
   };
-  auto MatchConstantBitMask = [&]() {
-    return ICmpInst::isEquality(Pred) && match(CmpRHS, m_Zero()) &&
-           match(CmpLHS, m_And(m_Value(CurrX),
-                               m_CombineAnd(m_Value(BitMask), m_Power2()))) &&
-           (BitPos = ConstantExpr::getExactLogBase2(cast<Constant>(BitMask)));
-  };
+
   auto MatchDecomposableConstantBitMask = [&]() {
-    auto Res = llvm::decomposeBitTestICmp(CmpLHS, CmpRHS, Pred);
+    auto Res = llvm::decomposeBitTestICmp(
+        CmpLHS, CmpRHS, Pred, /*LookThroughTrunc=*/true,
+        /*AllowNonZeroC=*/false, /*DecomposeAnd=*/true);
     if (Res && Res->Mask.isPowerOf2()) {
       assert(ICmpInst::isEquality(Res->Pred));
       Pred = Res->Pred;
@@ -2780,8 +2777,7 @@ static bool detectShiftUntilBitTestIdiom(Loop *CurLoop, Value *&BaseX,
     return false;
   };
 
-  if (!MatchVariableBitMask() && !MatchConstantBitMask() &&
-      !MatchDecomposableConstantBitMask()) {
+  if (!MatchVariableBitMask() && !MatchDecomposableConstantBitMask()) {
     LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad backedge comparison.\n");
     return false;
   }