Fixes an issue with FeatureSIMD=0 and ArmBase.Yield (#62351)

* Mark ArmBase.Yiels with HW_Flag_NoFloatingPointUsed in src/coreclr/jit/hwintrinsiclistarm64.h

* Move handling of ArmBase.Yield to an earlier point in impSpecialIntrinsic and simplify the remaining logic in src/coreclr/jit/hwintrinsicarm64.cpp

* Address feedback

Author: echesakov

src/coreclr/jit/hwintrinsicarm64.cpp

@@ -308,8 +308,22 @@ GenTree* Compiler::impSpecialIntrinsic(NamedIntrinsic        intrinsic,
                                        var_types             retType,
                                        unsigned              simdSize)
 {
-    HWIntrinsicCategory category = HWIntrinsicInfo::lookupCategory(intrinsic);
-    int                 numArgs  = sig->numArgs;
+    const HWIntrinsicCategory category = HWIntrinsicInfo::lookupCategory(intrinsic);
+    const int                 numArgs  = sig->numArgs;
+
+    // The vast majority of "special" intrinsics are Vector64/Vector128 methods.
+    // The only exception is ArmBase.Yield which should be treated differently.
+    if (intrinsic == NI_ArmBase_Yield)
+    {
+        assert(sig->numArgs == 0);
+        assert(JITtype2varType(sig->retType) == TYP_VOID);
+        assert(simdSize == 0);
+
+        return gtNewScalarHWIntrinsicNode(TYP_VOID, intrinsic);
+    }
+
+    assert(category != HW_Category_Scalar);
+    assert(!HWIntrinsicInfo::isScalarIsa(HWIntrinsicInfo::lookupIsa(intrinsic)));
 
     if (!featureSIMD || !IsBaselineSimdIsaSupported())
     {
@@ -318,13 +332,8 @@ GenTree* Compiler::impSpecialIntrinsic(NamedIntrinsic        intrinsic,
 
     assert(numArgs >= 0);
 
-    var_types simdBaseType = TYP_UNKNOWN;
-
-    if (intrinsic != NI_ArmBase_Yield)
-    {
-        simdBaseType = JitType2PreciseVarType(simdBaseJitType);
-        assert(varTypeIsArithmetic(simdBaseType));
-    }
+    const var_types simdBaseType = JitType2PreciseVarType(simdBaseJitType);
+    assert(varTypeIsArithmetic(simdBaseType));
 
     GenTree* retNode = nullptr;
     GenTree* op1     = nullptr;
@@ -333,16 +342,6 @@ GenTree* Compiler::impSpecialIntrinsic(NamedIntrinsic        intrinsic,
 
     switch (intrinsic)
     {
-        case NI_ArmBase_Yield:
-        {
-            assert(sig->numArgs == 0);
-            assert(JITtype2varType(sig->retType) == TYP_VOID);
-            assert(simdSize == 0);
-
-            retNode = gtNewScalarHWIntrinsicNode(TYP_VOID, intrinsic);
-            break;
-        }
-
         case NI_Vector64_Abs:
         case NI_Vector128_Abs:
         {

src/coreclr/jit/hwintrinsiclistarm64.h

@@ -627,7 +627,7 @@ HARDWARE_INTRINSIC(Aes,           PolynomialMultiplyWideningUpper,
 //  Base Intrinsics
 HARDWARE_INTRINSIC(ArmBase,       LeadingZeroCount,                                                  0,      1,     {INS_invalid,        INS_invalid,        INS_invalid,        INS_invalid,        INS_clz,            INS_clz,            INS_invalid,        INS_invalid,        INS_invalid,        INS_invalid},     HW_Category_Scalar,                HW_Flag_BaseTypeFromFirstArg|HW_Flag_NoFloatingPointUsed)
 HARDWARE_INTRINSIC(ArmBase,       ReverseElementBits,                                                0,      1,     {INS_invalid,        INS_invalid,        INS_invalid,        INS_invalid,        INS_rbit,           INS_rbit,           INS_invalid,        INS_invalid,        INS_invalid,        INS_invalid},     HW_Category_Scalar,                HW_Flag_NoFloatingPointUsed)
-HARDWARE_INTRINSIC(ArmBase,       Yield,                                                             0,      0,     {INS_invalid,        INS_invalid,        INS_invalid,        INS_invalid,        INS_invalid,        INS_invalid,        INS_invalid,        INS_invalid,        INS_invalid,        INS_invalid},     HW_Category_Special,               HW_Flag_SpecialCodeGen|HW_Flag_SpecialImport)
+HARDWARE_INTRINSIC(ArmBase,       Yield,                                                             0,      0,     {INS_invalid,        INS_invalid,        INS_invalid,        INS_invalid,        INS_invalid,        INS_invalid,        INS_invalid,        INS_invalid,        INS_invalid,        INS_invalid},     HW_Category_Special,               HW_Flag_NoFloatingPointUsed|HW_Flag_SpecialCodeGen|HW_Flag_SpecialImport)
 
 // ***************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************
 //                 ISA            Function name                                              SIMD size  Number of arguments                                                                                            Instructions                                                                                        Category                           Flags