Ensure that the CpuId tests set preferredVectorByteLength to a non-zero value

src/coreclr/jit/compiler.cpp

@@ -2306,13 +2306,10 @@ void Compiler::compSetProcessor()
             // users can override this with `DOTNET_PreferredVectorBitWidth=512` to
             // allow using such instructions where hardware support is available.
             //
-            // Under stress, sometimes leave the preferred vector width at 512, even if that means
-            // throttling. This helps with test coverage on test machines that might be older.
+            // Do not condition this based on stress mode as it makes the support
+            // reported inconsistent across methods and breaks expectations/functionality
 
-            if (!compStressCompile(STRESS_GENERIC_VARN, 20))
-            {
-                preferredVectorByteLength = 256 / 8;
-            }
+            preferredVectorByteLength = 256 / 8;
         }
     }
 

src/coreclr/jit/hwintrinsic.cpp

@@ -495,8 +495,9 @@ NamedIntrinsic HWIntrinsicInfo::lookupId(Compiler*         comp,
         return NI_Illegal;
     }
 
-    bool isIsaSupported            = comp->compSupportsHWIntrinsic(isa);
-    bool isHardwareAcceleratedProp = (strcmp(methodName, "get_IsHardwareAccelerated") == 0);
+    bool     isIsaSupported            = comp->compSupportsHWIntrinsic(isa);
+    bool     isHardwareAcceleratedProp = (strcmp(methodName, "get_IsHardwareAccelerated") == 0);
+    uint32_t vectorByteLength          = 0;
 
 #ifdef TARGET_XARCH
     if (isHardwareAcceleratedProp)
@@ -505,25 +506,21 @@ NamedIntrinsic HWIntrinsicInfo::lookupId(Compiler*         comp,
         // but we want IsHardwareAccelerated to return true only when all of them are (there are
         // still can be cases where e.g. Sse41 might give an additional boost for Vector128, but it's
         // not important enough to bump the minimal Sse version here)
+
         if (strcmp(className, "Vector128") == 0)
         {
-            isa = InstructionSet_SSE2;
+            isa              = InstructionSet_SSE2;
+            vectorByteLength = 16;
         }
         else if (strcmp(className, "Vector256") == 0)
         {
-            if (comp->getPreferredVectorByteLength() < 32)
-            {
-                return NI_IsSupported_False;
-            }
-            isa = InstructionSet_AVX2;
+            isa              = InstructionSet_AVX2;
+            vectorByteLength = 32;
         }
         else if (strcmp(className, "Vector512") == 0)
         {
-            if (comp->getPreferredVectorByteLength() < 64)
-            {
-                return NI_IsSupported_False;
-            }
-            isa = InstructionSet_AVX512F;
+            isa              = InstructionSet_AVX512F;
+            vectorByteLength = 64;
         }
     }
 #endif
@@ -556,7 +553,8 @@ NamedIntrinsic HWIntrinsicInfo::lookupId(Compiler*         comp,
         // When the compiler doesn't support ISA or when it does but the target hardware does
         // not and we aren't in a scenario with support for a dynamic check, we want to return false.
 
-        if (isIsaSupported && comp->compSupportsHWIntrinsic(isa))
+        if (isIsaSupported && comp->compSupportsHWIntrinsic(isa) &&
+            (vectorByteLength <= comp->getPreferredVectorByteLength()))
         {
             if (!comp->IsTargetAbi(CORINFO_NATIVEAOT_ABI) || comp->compExactlyDependsOn(isa))
             {

src/tests/JIT/HardwareIntrinsics/X86/X86Base/CpuId.cs

@@ -256,10 +256,14 @@ public unsafe static void CpuId()
                     }
                 }
 
-                if (isVector512Throttling)
+                if (isAvx512HierarchyDisabled || isVector512Throttling)
                 {
                     preferredVectorByteLength = 256 / 8;
                 }
+                else
+                {
+                    preferredVectorByteLength = 512 / 8;
+                }
             }
 
             if (IsBitIncorrect(ecx, 1, typeof(Avx512Vbmi), Avx512Vbmi.IsSupported, "AVX512VBMI", ref isHierarchyDisabled))

src/tests/readytorun/HardwareIntrinsics/X86/CpuId.cs

@@ -251,10 +251,14 @@ public unsafe static int Main()
                     }
                 }
 
-                if (isVector512Throttling)
+                if (isAvx512HierarchyDisabled || isVector512Throttling)
                 {
                     preferredVectorByteLength = 256 / 8;
                 }
+                else
+                {
+                    preferredVectorByteLength = 512 / 8;
+                }
             }
 
             if (IsBitIncorrect(ecx, 1, typeof(Avx512Vbmi), Avx512Vbmi.IsSupported, "AVX512VBMI", ref isHierarchyDisabled))