Fold some HW nodes for constant input

src/coreclr/jit/assertionprop.cpp

@@ -6119,6 +6119,9 @@ Compiler::fgWalkResult Compiler::optVNConstantPropCurStmt(BasicBlock* block, Sta
         case GT_NEG:
         case GT_CAST:
         case GT_INTRINSIC:
+#ifdef FEATURE_HW_INTRINSICS
+        case GT_HWINTRINSIC:
+#endif
         case GT_ARR_LENGTH:
             break;
 

src/coreclr/jit/valuenum.cpp

@@ -6001,6 +6001,59 @@ void ValueNumStore::SetVNIsCheckedBound(ValueNum vn)
     m_checkedBoundVNs.AddOrUpdate(vn, true);
 }
 
+#ifdef FEATURE_HW_INTRINSICS
+ValueNum ValueNumStore::EvalHWIntrinsicFunUnary(
+    var_types type, NamedIntrinsic ni, VNFunc func, ValueNum arg0VN, bool encodeResultType, ValueNum resultTypeVN)
+{
+    if (IsVNConstant(arg0VN))
+    {
+        switch (ni)
+        {
+#ifdef TARGET_ARM64
+            case NI_ArmBase_LeadingZeroCount:
+#else
+            case NI_LZCNT_LeadingZeroCount:
+#endif
+            {
+                UINT32 cns = (UINT32)GetConstantInt32(arg0VN);
+                int    lzc = 0;
+                while (cns != 0)
+                {
+                    cns = cns >> 1;
+                    lzc++;
+                }
+                return VNForIntCon(32 - lzc);
+            }
+
+#ifdef TARGET_ARM64
+            case NI_ArmBase_Arm64_LeadingZeroCount:
+#else
+            case NI_LZCNT_X64_LeadingZeroCount:
+#endif
+            {
+                UINT64 cns = (UINT64)GetConstantInt64(arg0VN);
+                int    lzc = 0;
+                while (cns != 0)
+                {
+                    cns = cns >> 1;
+                    lzc++;
+                }
+                return VNForIntCon(64 - lzc);
+            }
+
+            default:
+                break;
+        }
+    }
+
+    if (encodeResultType)
+    {
+        return VNForFunc(type, func, arg0VN, resultTypeVN);
+    }
+    return VNForFunc(type, func, arg0VN);
+}
+#endif
+
 ValueNum ValueNumStore::EvalMathFuncUnary(var_types typ, NamedIntrinsic gtMathFN, ValueNum arg0VN)
 {
     assert(arg0VN == VNNormalValue(arg0VN));
@@ -9765,25 +9818,21 @@ void Compiler::fgValueNumberHWIntrinsic(GenTreeHWIntrinsic* tree)
 
             if (tree->GetOperandCount() == 1)
             {
-                excSetPair = op1Xvnp;
+                ValueNum normalLVN =
+                    vnStore->EvalHWIntrinsicFunUnary(tree->TypeGet(), intrinsicId, func, op1vnp.GetLiberal(),
+                                                     encodeResultType, resultTypeVNPair.GetLiberal());
+                ValueNum normalCVN =
+                    vnStore->EvalHWIntrinsicFunUnary(tree->TypeGet(), intrinsicId, func, op1vnp.GetConservative(),
+                                                     encodeResultType, resultTypeVNPair.GetConservative());
 
-                if (encodeResultType)
-                {
-                    normalPair = vnStore->VNPairForFunc(tree->TypeGet(), func, op1vnp, resultTypeVNPair);
-                    assert((vnStore->VNFuncArity(func) == 2) || isVariableNumArgs);
-                }
-                else
-                {
-                    normalPair = vnStore->VNPairForFunc(tree->TypeGet(), func, op1vnp);
-                    assert((vnStore->VNFuncArity(func) == 1) || isVariableNumArgs);
-                }
+                normalPair = ValueNumPair(normalLVN, normalCVN);
+                excSetPair = op1Xvnp;
             }
             else
             {
                 ValueNumPair op2vnp;
                 ValueNumPair op2Xvnp;
                 getOperandVNs(tree->Op(2), &op2vnp, &op2Xvnp);
-
                 excSetPair = vnStore->VNPExcSetUnion(op1Xvnp, op2Xvnp);
                 if (encodeResultType)
                 {

src/coreclr/jit/valuenum.h

@@ -1108,6 +1108,9 @@ class ValueNumStore
                             EvalMathFuncBinary(typ, mthFunc, arg0VNP.GetConservative(), arg1VNP.GetConservative()));
     }
 
+    ValueNum EvalHWIntrinsicFunUnary(
+        var_types type, NamedIntrinsic ni, VNFunc func, ValueNum arg0VN, bool encodeResultType, ValueNum resultTypeVN);
+
     // Returns "true" iff "vn" represents a function application.
     bool IsVNFunc(ValueNum vn);
 

src/tests/JIT/HardwareIntrinsics/General/ConstantFolding/ScalarConstantFoldings.cs

@@ -0,0 +1,54 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Runtime.CompilerServices;
+using System.Runtime.Intrinsics.Arm;
+using System.Runtime.Intrinsics.X86;
+using Xunit;
+
+public class ScalarConstantFoldings
+{
+    [Fact]
+    public static void LeadingZeroCountTests()
+    {
+        if (Lzcnt.IsSupported)
+        {
+            Assert.Equal(32U, Lzcnt.LeadingZeroCount(0));
+            Assert.Equal(31U, Lzcnt.LeadingZeroCount(1));
+            Assert.Equal(17U, Lzcnt.LeadingZeroCount(31400));
+            Assert.Equal(0U, Lzcnt.LeadingZeroCount(1U << 31));
+            Assert.Equal(0U, Lzcnt.LeadingZeroCount(uint.MaxValue));
+            Assert.Equal(0U, Lzcnt.LeadingZeroCount(uint.MaxValue - 1));
+        }
+        if (Lzcnt.X64.IsSupported)
+        {
+            Assert.Equal(64UL, Lzcnt.X64.LeadingZeroCount(0));
+            Assert.Equal(63UL, Lzcnt.X64.LeadingZeroCount(1));
+            Assert.Equal(49UL, Lzcnt.X64.LeadingZeroCount(31400));
+            Assert.Equal(32UL, Lzcnt.X64.LeadingZeroCount(1UL << 31));
+            Assert.Equal(0UL, Lzcnt.X64.LeadingZeroCount(1UL << 63));
+            Assert.Equal(0UL, Lzcnt.X64.LeadingZeroCount(ulong.MaxValue));
+            Assert.Equal(0UL, Lzcnt.X64.LeadingZeroCount(ulong.MaxValue - 1));
+        }
+        if (ArmBase.IsSupported)
+        {
+            Assert.Equal(32, ArmBase.LeadingZeroCount(0));
+            Assert.Equal(31, ArmBase.LeadingZeroCount(1));
+            Assert.Equal(17, ArmBase.LeadingZeroCount(31400));
+            Assert.Equal(0, ArmBase.LeadingZeroCount(1U << 31));
+            Assert.Equal(0, ArmBase.LeadingZeroCount(uint.MaxValue));
+            Assert.Equal(0, ArmBase.LeadingZeroCount(uint.MaxValue - 1));
+        }
+        if (ArmBase.Arm64.IsSupported)
+        {
+            Assert.Equal(64, ArmBase.Arm64.LeadingZeroCount(0));
+            Assert.Equal(63, ArmBase.Arm64.LeadingZeroCount(1));
+            Assert.Equal(49, ArmBase.Arm64.LeadingZeroCount(31400));
+            Assert.Equal(32, ArmBase.Arm64.LeadingZeroCount(1UL << 31));
+            Assert.Equal(0, ArmBase.Arm64.LeadingZeroCount(1UL << 63));
+            Assert.Equal(0, ArmBase.Arm64.LeadingZeroCount(ulong.MaxValue));
+            Assert.Equal(0, ArmBase.Arm64.LeadingZeroCount(ulong.MaxValue - 1));
+        }
+    }
+}

src/tests/JIT/HardwareIntrinsics/General/ConstantFolding/ScalarConstantFoldings.csproj

@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <BuildAsStandalone>false</BuildAsStandalone>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>