add stripNullTest and update isKnownNonZero

Author: el-ev

llvm/include/llvm/Analysis/ValueTracking.h

@@ -999,6 +999,11 @@ LLVM_ABI void
 findValuesAffectedByCondition(Value *Cond, bool IsAssume,
                               function_ref<void(Value *)> InsertAffected);
 
+/// Returns the inner value X if the expression has the form f(X)
+/// where f(X) == 0 if and only if X == 0, otherwise returns nullptr.
+LLVM_ABI Value *stripNullTest(Value *V);
+LLVM_ABI const Value *stripNullTest(const Value *V);
+
 } // end namespace llvm
 
 #endif // LLVM_ANALYSIS_VALUETRACKING_H

llvm/lib/Analysis/ValueTracking.cpp

@@ -3544,6 +3544,9 @@ bool isKnownNonZero(const Value *V, const APInt &DemandedElts,
       isKnownNonNullFromDominatingCondition(V, Q.CxtI, Q.DT))
     return true;
 
+  if (const Value *Stripped = stripNullTest(V))
+    return isKnownNonZero(Stripped, DemandedElts, Q, Depth + 1);
+
   return false;
 }
 
@@ -10193,3 +10196,26 @@ void llvm::findValuesAffectedByCondition(
     }
   }
 }
+
+const Value *llvm::stripNullTest(const Value *V) {
+  // (X >> C) or/add (X & mask(C) != 0)
+  if (const auto *BO = dyn_cast<BinaryOperator>(V)) {
+    if (BO->getOpcode() == Instruction::Add ||
+        BO->getOpcode() == Instruction::Or) {
+      const Value *X;
+      const APInt *C1, *C2;
+      if (match(BO, m_c_BinOp(m_LShr(m_Value(X), m_APInt(C1)),
+                              m_ZExt(m_SpecificICmp(
+                                  ICmpInst::ICMP_NE,
+                                  m_And(m_Deferred(X), m_LowBitMask(C2)),
+                                  m_Zero())))) &&
+          C2->popcount() == C1->getZExtValue())
+        return X;
+    }
+  }
+  return nullptr;
+}
+
+Value *llvm::stripNullTest(Value *V) {
+  return const_cast<Value *>(stripNullTest(const_cast<const Value *>(V)));
+}

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -1299,22 +1299,11 @@ Instruction *InstCombinerImpl::foldICmpWithZero(ICmpInst &Cmp) {
     // will fold to a constant elsewhere.
   }
 
-  // icmp eq/ne ((X >> C) or/add (X & mask(C) != 0)), 0 -> icmp eq/ne X, 0
-  if (ICmpInst::isEquality(Pred)) {
-    auto *BO = dyn_cast<BinaryOperator>(Cmp.getOperand(0));
-    Value *X;
-    const APInt *C1, *C2;
-    if (BO &&
-        (BO->getOpcode() == Instruction::Add ||
-         BO->getOpcode() == Instruction::Or) &&
-        match(BO, m_c_BinOp(m_LShr(m_Value(X), m_APInt(C1)),
-                            m_ZExt(m_SpecificICmp(
-                                ICmpInst::ICMP_NE,
-                                m_And(m_Deferred(X), m_LowBitMask(C2)),
-                                m_Zero())))) &&
-        C2->popcount() == C1->getZExtValue())
-      return new ICmpInst(Pred, X, ConstantInt::getNullValue(X->getType()));
-  }
+  // (icmp eq/ne f(X), 0) -> (icmp eq/ne X, 0)
+  // where f(X) == 0 if and only if X == 0
+  if (ICmpInst::isEquality(Pred))
+    if (Value *Stripped = stripNullTest(Cmp.getOperand(0)))
+      return new ICmpInst(Pred, Stripped, Cmp.getOperand(1));
 
   return nullptr;
 }