How to detect AVX2 in Delphi?

Question

Following code returns True if CPU has AVX1 or AVX2. Does anybody know how to modify this code to detect exactly AVX2 instruction support?

function isAvxSupported: Boolean;
asm
{$IFDEF CPUX86}
    push ebx
{$ENDIF}
{$IFDEF CPUX64}
    mov r10, rbx
{$ENDIF}
    xor eax, eax
    cpuid
    cmp eax, 1
    jb @not_supported
    mov eax, 1
    cpuid
    and ecx, 018000000h
    cmp ecx, 018000000h
    jne @not_supported
    xor ecx, ecx
    db 0Fh, 01h, 0D0h //XGETBV
    and eax, 110b
    cmp eax, 110b
    jne @not_supported
    mov eax, 1
    jmp @done
@not_supported:
    xor eax, eax
@done:
{$IFDEF CPUX86}
    pop ebx
{$ENDIF}
{$IFDEF CPUX64}
    mov rbx, r10
{$ENDIF}
end;

Answer 1

Essentially, before using AVX2, you need to check

1. if the AVX2 instruction set is supported by checking CPUID.(EAX=07H, ECX=0H):EBX.AVX2[bit 5]=1
2. if use of YMM registers is enabled by the OS

Step 1 can be done e.g. using this function:

function IsAVX2supported: boolean;
asm
    // Save EBX
    {$IFDEF CPUx86}
      push ebx
    {$ELSE CPUx64}
      mov r10, rbx
    {$ENDIF}
    //Check CPUID.0
    xor eax, eax
    cpuid //modifies EAX,EBX,ECX,EDX
    cmp al, 7 // do we have a CPUID leaf 7 ?
    jge @Leaf7
      xor eax, eax
      jmp @Exit
    @Leaf7:
      //Check CPUID.7
      mov eax, 7h
      xor ecx, ecx
      cpuid
      bt ebx, 5 //AVX2: CPUID.(EAX=07H, ECX=0H):EBX.AVX2[bit 5]=1
      setc al
   @Exit:
   // Restore EBX
   {$IFDEF CPUx86}
     pop ebx
   {$ELSE CPUx64}
     mov rbx, r10
   {$ENDIF}
end;

Step 2 can be done e.g. using this function:

function OSEnabledXmmYmm: boolean;
// necessary to check before using AVX, FMA or AES instructions!
asm
  {$IFDEF CPUx86}
  push ebx
  {$ELSE CPUx64}
  mov r10, rbx
  {$ENDIF}
  mov eax,1
  cpuid
  bt ecx, 27  // CPUID.1:ECX.OSXSAVE[bit 27] = 1 (XGETBV enabled for application use; implies XGETBV is an available instruction also)
  jnc @not_supported
    xor ecx,ecx //Specify control register XCR0 = XFEATURE_ENABLED_MASK register
    db 0Fh, 01h, 0D0h // xgetbv //Reads XCR (extended control register) -> EDX:EAX
    {lgdt eax = db 0Fh, 01h = privileged instruction, so don't go here unless xgetbv is allowed}
      //CHECK XFEATURE_ENABLED_MASK[2:1] = ‘11b’
      and eax, 06h //06h= 00000000000000000000000000000110b
      cmp eax, 06h//; check OS has enabled both XMM (bit 1) and YMM (bit 2) state management support
    jne @not_supported
      mov eax,1
      jmp @out
  @not_supported:
    xor eax,eax
  @out:
 {$IFDEF CPUx86}
  pop ebx
  {$ELSE CPUx64}
  mov rbx, r10
  {$ENDIF}
end;

Of course, you can also use this to modify the function you posted to just have a single function to call.

Answer 2

OK I think that detecting AVX2 is as simple as this

function isAVX2Supported():boolean;
var _ebx: Longword;
begin

  asm
    mov eax,7 // EAX=7 -> https://en.wikipedia.org/wiki/CPUID
    db $0F,$A2 // db $0F,$A2 = CPUID instruction
    mov _ebx,ebx
  end;
  if (_ebx and $20) = $20 then isAVX2Supported:=true //Bit 5 = 100000 = $20 (HEX) 
  else isAVX2Supported:=false;

end;