[release/9.0] JIT: Cast UInt64 to Single directly during const folding (#106720)

* Fix cast folding on ARM64

* Add test

* Fix weird comment spacing

* Fix test

* Fix test

* Flip params

* Run test on CoreCLR only

* Add RequiresProcessIsolation

* Do single-step conversion on all platforms

* Expand test coverage

* Update test

* Try running test on all CoreCLR platforms

* Fix condition

---------

Co-authored-by: Aman Khalid (from Dev Box) <[email protected]>

Author: github-actions[bot]

src/coreclr/jit/gentree.cpp

@@ -15607,7 +15607,7 @@ GenTree* Compiler::gtFoldExprConst(GenTree* tree)
 
                             case TYP_FLOAT:
                             {
-#if defined(TARGET_64BIT)
+#ifdef TARGET_64BIT
                                 if (tree->IsUnsigned() && (lval1 < 0))
                                 {
                                     f1 = FloatingPointUtils::convertUInt64ToFloat((uint64_t)lval1);

src/coreclr/jit/utils.cpp

@@ -2272,8 +2272,7 @@ double FloatingPointUtils::convertUInt64ToDouble(uint64_t uIntVal)
 
 float FloatingPointUtils::convertUInt64ToFloat(uint64_t u64)
 {
-    double d = convertUInt64ToDouble(u64);
-    return (float)d;
+    return (float)u64;
 }
 
 uint64_t FloatingPointUtils::convertDoubleToUInt64(double d)

src/tests/JIT/Regression/JitBlue/Runtime_106338/Runtime_106338.cs

@@ -0,0 +1,36 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+// Generated by Fuzzlyn v2.2 on 2024-08-13 00:04:04
+// Run on Arm64 MacOS
+// Seed: 13207615092246842583-vectort,vector64,vector128,armadvsimd,armadvsimdarm64,armaes,armarmbase,armarmbasearm64,armcrc32,armcrc32arm64,armdp,armrdm,armrdmarm64,armsha1,armsha256
+// Reduced from 226.8 KiB to 0.4 KiB in 00:02:12
+// Debug: Outputs 1600094603
+// Release: Outputs 1600094604
+using System;
+using System.Runtime.InteropServices;
+using System.Runtime.Intrinsics.X86;
+using Xunit;
+
+public class Runtime_106338
+{
+    [Fact]
+    [SkipOnMono("https://github.com/dotnet/runtime/issues/100368", TestPlatforms.Any)]
+    public static void TestEntryPoint()
+    {
+        ulong vr10 = 16105307123914158031UL;
+        float vr11 = 4294967295U | vr10;
+        uint result = BitConverter.SingleToUInt32Bits(vr11);
+
+        if ((RuntimeInformation.ProcessArchitecture == Architecture.Arm64) || ((RuntimeInformation.ProcessArchitecture == Architecture.X64) && Avx512F.IsSupported))
+        {
+            // Expected to cast ulong -> float directly
+            Assert.Equal(1600094603U, result);
+        }
+        else
+        {
+            // Expected to cast ulong -> double -> float
+            Assert.Equal(1600094604U, result);
+        }
+    }
+}

src/tests/JIT/Regression/JitBlue/Runtime_106338/Runtime_106338.csproj

@@ -0,0 +1,8 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>