delphi – 为什么这个LEA指令不能编译？

我正在将32位Delphi BASM代码移植到64位FPC(Win64目标操作系统),并想知道为什么下一条指令不能在64位FPC中编译：

{$IFDEF FPC}
  {$ASMMODE INTEL}
{$ENDIF}

procedure DoesNotCompile;
asm
      LEA   ECX,[ECX + ESI + $265E5A51]
end;

// Error: Asm: 16 or 32 Bit references not supported

可能的解决方法是：

procedure Compiles1;
asm
      ADD   ECX,ESI
      ADD   ECX,$265E5A51
end;

procedure Compiles2;
asm
      LEA   ECX,[RCX + RSI + $265E5A51]
end;

我只是不明白Win64目标中的32位LEA指令有什么问题(它在32位Delphi中编译正常,因此它是正确的CPU指令).

优化备注：

下一代码由64位FPC 2.6.2编译

{$MODE DELPHI}
  {$ASMMODE INTEL}

procedure Test;
asm
        LEA     ECX,[RCX + RSI + $265E5A51]
        NOP
        LEA     RCX,[RCX + RSI + $265E5A51]
        NOP
        ADD     ECX,$265E5A51
        ADD     ECX,ESI
        NOP
end;

生成下一个汇编程序输出：

00000000004013F0 4883ec08                 sub    $0x8,%rsp
                         project1.lpr:10  LEA     ECX,[RCX + RSI + $265E5A51]
00000000004013F4 8d8c31515a5e26           lea    0x265e5a51(%rcx,%rsi,1),%ecx
                         project1.lpr:11  NOP
00000000004013FB 90                       nop
                         project1.lpr:12  LEA     RCX,[RCX + RSI + $265E5A51]
00000000004013FC 488d8c31515a5e26         lea    0x265e5a51(%rcx,%rsi,1),%rcx
                         project1.lpr:13  NOP
0000000000401404 90                       nop
                         project1.lpr:14  ADD     ECX,$265E5A51
0000000000401405 81c1515a5e26             add    $0x265e5a51,%ecx
                         project1.lpr:15  ADD     ECX,ESI
000000000040140B 01f1                     add    %esi,%ecx
                         project1.lpr:16  NOP
000000000040140D 90                       nop
                         project1.lpr:17  end;
000000000040140E 4883c408                 add    $0x8,%rsp

获胜者是(7个字节长)：

LEA     ECX,[RCX + RSI + $265E5A51]

所有3个备选方案(包括LEA ECX,[ECX ESI $265E5A51],不通过64位FPC编译)长度为8个字节.

不确定获胜者的速度是否最佳.

我认为这是FPC汇编程序中的错误.您提供的asm代码是有效的,在64位模式下,使用带有32位寄存器的LEA是完全有效的.英特尔处理器文件很清楚. Delphi 64位内联汇编程序接受此代码.

要解决此问题,您需要手动组装代码：

DQ    $265e5a510e8c8d67

在Delphi CPU视图中,它显示为：

Project1.dpr.12: DQ    $265e5a510e8c8d67
0000000000424160 678D8C0E515A5E26 lea ecx,[esi+ecx+$265e5a51]

我执行了一个非常简单的基准测试来比较32位和64位操作数的使用,以及使用两个ADD的版本.代码如下所示：

{$APPTYPE CONSOLE}

uses
  System.Diagnostics;

function BenchWithTwoAdds: Integer;
asm
    MOV   EDX,ESI
    XOR   EAX,EAX
    MOV   ESI,$98C34
    MOV   ECX,$ffffffff
@loop:
    ADD   EAX,ESI
    ADD   EAX,$265E5A51
    DEC   ECX
    CMP   ECX,0
    JNZ   @loop
    MOV   ESI,EDX
end;

function BenchWith32bitOperands: Integer;
asm
    MOV   EDX,ESI
    XOR   EAX,EAX
    MOV   ESI,$98C34
    MOV   ECX,$ffffffff
@loop:
    LEA   EAX,[EAX + ESI + $265E5A51]
    DEC   ECX
    CMP   ECX,0
    JNZ   @loop
    MOV   ESI,EDX
end;

{$IFDEF CPUX64}
function BenchWith64bitOperands: Integer;
asm
    MOV   EDX,ESI
    XOR   EAX,EAX
    MOV   ESI,$98C34
    MOV   ECX,$ffffffff
@loop:
    LEA   EAX,[RAX + RSI + $265E5A51]
    DEC   ECX
    CMP   ECX,0
    JNZ   @loop
    MOV   ESI,EDX
end;
{$ENDIF}

var
  Stopwatch: TStopwatch;

begin
{$IFDEF CPUX64}
  Writeln('64 bit');
{$ELSE}
  Writeln('32 bit');
{$ENDIF}
  Writeln;

  Writeln('BenchWithTwoAdds');
  Stopwatch := TStopwatch.StartNew;
  Writeln('Value = ', BenchWithTwoAdds);
  Writeln('Elapsed time = ', Stopwatch.ElapsedMilliseconds);
  Writeln;

  Writeln('BenchWith32bitOperands');
  Stopwatch := TStopwatch.StartNew;
  Writeln('Value = ', BenchWith32bitOperands);
  Writeln('Elapsed time = ', Stopwatch.ElapsedMilliseconds);
  Writeln;

{$IFDEF CPUX64}
  Writeln('BenchWith64bitOperands');
  Stopwatch := TStopwatch.StartNew;
  Writeln('Value = ', BenchWith64bitOperands);
  Writeln('Elapsed time = ', Stopwatch.ElapsedMilliseconds);
{$ENDIF}

  Readln;
end.

英特尔i5-2300的输出：

32 bit

BenchWithTwoAdds
Value = -644343429
Elapsed time = 2615

BenchWith32bitOperands
Value = -644343429
Elapsed time = 3915

----------------------

64 bit

BenchWithTwoAdds
Value = -644343429
Elapsed time = 2612

BenchWith32bitOperands
Value = -644343429
Elapsed time = 3917

BenchWith64bitOperands
Value = -644343429
Elapsed time = 3918

正如您所看到的,基于此的LEA选项之间没有任何选择.它们的时间之间的差异完全在测量的可变性之内.但是,使用ADD的变体两次获胜.

不同机器的一些不同结果.这是Xeon E5530的输出：

64 bit

BenchWithTwoAdds
Value = -644343429
Elapsed time = 3434

BenchWith32bitOperands
Value = -644343429
Elapsed time = 3295

BenchWith64bitOperands
Value = -644343429
Elapsed time = 3279

在Xeon E5-4640 v2上：

64 bit

BenchWithTwoAdds
Value = -644343429
Elapsed time = 4102

BenchWith32bitOperands
Value = -644343429
Elapsed time = 5868

BenchWith64bitOperands
Value = -644343429
Elapsed time = 5868