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Why does Visual Studio compile mov eax, [edx] [ebx] [ecx] [edi] without complaint?

In Visual Studio, I wrote:

mov eax, [edx][ebx][ecx][edi]

But he is going just fine.

Why is this an invalid effective address?

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This seems to be a bug in later versions of MASM.

Using the following file as an example:

  .586 _TEXT SEGMENT USE32 mov eax, [edx][ebx][ecx][edi] _TEXT ENDS END

With MASM 6.11d, this causes the following error:

 t213a.asm(4) : error A2030: multiple index registers not allowed

There is no error in MASM 8.00.50727.42 or later, and the instructions are compiled for:

 00000000: 8B 04 0F mov eax,dword ptr [edi+ecx]

So, [edx][ebx][ecx][edi] not a valid addressing mode. The error in the version of MASM that you use accepts it when it should reject it as an error.

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