Arm64/Sve: Enable Sve only if vector length is 128 (#104174)

* Enable InstructionSet_Sve only if system VL == 128

* Update src/coreclr/vm/codeman.cpp

Co-authored-by: Jan Kotas <jkotas@microsoft.com>

* Update src/coreclr/vm/codeman.cpp

* Remove hardcoding of 128 for windows

---------

Co-authored-by: Jan Kotas <jkotas@microsoft.com>

Author: kunalspathak

src/coreclr/vm/arm64/asmhelpers.asm

@@ -80,9 +80,7 @@
 
 ;; uint64_t GetSveLengthFromOS(void);
     LEAF_ENTRY GetSveLengthFromOS
-        ;; TODO-SVE: Remove the hardcoded value 128 and uncomment once CI machines are updated to use MASM 14.4 or later
-        ;; rdvl    x0, 1
-        mov     x0, #128
+        rdvl    x0, 1
         ret     lr
     LEAF_END
 

src/coreclr/vm/codeman.cpp

@@ -1514,8 +1514,10 @@ void EEJitManager::SetCpuInfo()
         uint32_t maxVectorTLength = (maxVectorTBitWidth / 8);
         uint64_t sveLengthFromOS = GetSveLengthFromOS();
 
-        // Do not enable SVE when the user specified vector length is smaller than the one offered by underlying OS.
-        if ((maxVectorTLength >= sveLengthFromOS) || (maxVectorTBitWidth == 0))
+        // For now, enable SVE only when the system vector length is 128-bits
+        // TODO: https://github.com/dotnet/runtime/issues/101477
+        if (sveLengthFromOS == 128)
+        // if ((maxVectorTLength >= sveLengthFromOS) || (maxVectorTBitWidth == 0))
         {
             CPUCompileFlags.Set(InstructionSet_Sve);
         }