JIT: Add out-of-bounds fallback for AdvSimd.ShiftRightLogical (#105777)

Fixes #105621. When its immediate is out-of-bounds, AdvSimd.ShiftRightLogical can be transformed into AdvSimd.ShiftLogical, which takes the immediate in a register. This means AdvSimd.ShiftRightLogical will no longer throw ArgumentOutOfRangeException in Debug or Release; when optimizing, we'd previously fold the intrinsic away, thus creating behavioral discrepancies.

Author: amanasifkhalid

src/coreclr/jit/hwintrinsic.cpp

@@ -1660,7 +1660,24 @@ bool Compiler::CheckHWIntrinsicImmRange(NamedIntrinsic intrinsic,
         {
             assert(!mustExpand);
             // The imm-HWintrinsics that do not accept all imm8 values may throw
-            // ArgumentOutOfRangeException when the imm argument is not in the valid range
+            // ArgumentOutOfRangeException when the imm argument is not in the valid range,
+            // unless the intrinsic can be transformed into one that does accept all imm8 values
+
+#ifdef TARGET_ARM64
+            switch (intrinsic)
+            {
+                case NI_AdvSimd_ShiftRightLogical:
+                    *useFallback = true;
+                    break;
+
+                    // TODO: Implement more AdvSimd fallbacks in Compiler::impNonConstFallback
+
+                default:
+                    assert(*useFallback == false);
+                    break;
+            }
+#endif // TARGET_ARM64
+
             return false;
         }
     }

src/coreclr/jit/hwintrinsicarm64.cpp

@@ -564,7 +564,26 @@ void HWIntrinsicInfo::lookupImmBounds(
 //
 GenTree* Compiler::impNonConstFallback(NamedIntrinsic intrinsic, var_types simdType, CorInfoType simdBaseJitType)
 {
-    return nullptr;
+    switch (intrinsic)
+    {
+        case NI_AdvSimd_ShiftRightLogical:
+        {
+            // AdvSimd.ShiftRightLogical be replaced with AdvSimd.ShiftLogical, which takes op2 in a simd register
+
+            GenTree* op2 = impPopStack().val;
+            GenTree* op1 = impSIMDPopStack();
+
+            // AdvSimd.ShiftLogical does right-shifts with negative immediates, hence the negation
+            GenTree* tmpOp =
+                gtNewSimdCreateBroadcastNode(simdType, gtNewOperNode(GT_NEG, genActualType(op2->TypeGet()), op2),
+                                             simdBaseJitType, genTypeSize(simdType));
+            return gtNewSimdHWIntrinsicNode(simdType, op1, tmpOp, NI_AdvSimd_ShiftLogical, simdBaseJitType,
+                                            genTypeSize(simdType));
+        }
+
+        default:
+            return nullptr;
+    }
 }
 
 //------------------------------------------------------------------------

src/tests/JIT/Regression/JitBlue/Runtime_105621/Runtime_105621.cs

@@ -0,0 +1,38 @@
+// 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 v2.1 on 2024-07-28 20:49:49
+// Run on Arm64 Linux
+// Seed: 14204794442367797079-vectort,vector64,vector128,armadvsimd,armadvsimdarm64,armaes,armarmbase,armarmbasearm64,armcrc32,armcrc32arm64,armdp,armrdm,armrdmarm64,armsha1,armsha256
+// Reduced from 12.6 KiB to 0.4 KiB in 00:00:17
+// Debug: Throws 'System.ArgumentOutOfRangeException'
+// Release: Runs successfully
+using System;
+using System.Runtime.Intrinsics;
+using System.Runtime.Intrinsics.Arm;
+using Xunit;
+
+public class Runtime_105621
+{
+    [Fact]
+    public static void TestShiftByZero()
+    {
+        if (AdvSimd.IsSupported)
+        {
+            var vr3 = Vector64.Create<byte>(0);
+            var vr4 = AdvSimd.ShiftRightLogical(vr3, 0);
+            Assert.Equal(vr3, vr4);
+        }
+    }
+
+    [Fact]
+    public static void TestShiftToZero()
+    {
+        if (AdvSimd.IsSupported)
+        {
+            var vr3 = Vector64.Create<byte>(128);
+            var vr4 = AdvSimd.ShiftRightLogical(vr3, 9);
+            Assert.Equal(vr4, Vector64<byte>.Zero);
+        }
+    }
+}

src/tests/JIT/Regression/JitBlue/Runtime_105621/Runtime_105621.csproj

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