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Q67039: /qc Option Cannot Be Combined with /Ol and register Variables

Article: Q67039
Product(s): See article
Version(s): 6.00 6.00a | 6.00 6.00a
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | S_QUICKC buglist6.00 buglist6.00a | mspl13_c
Last Modified: 28-NOV-1990

When using either QuickC or the quick compile option (/qc) with the
Microsoft C compiler, loop optimization (/Ol) cannot be specified for
any functions that contain variables declared with the register
storage-class that are referenced in an inline assembly (_asm) block.

This combination will result in the following compiler error for any
register variables referenced in the inline assembly code:

   error C2418: variable not in a register.

This problem occurs because /Ol results in register variables not
being allocated in registers, a problem that also occurs with the C
compiler without /qc. For more information, query on the following
words:

    C4024 and register and inline and stack

Because the variables are not in registers, the compiler cannot handle
register instructions that reference them in the inline assembly.
Therefore, the C2148 error is generated. When using the C compiler
without /qc, /Ol is prevented from causing this problem.

To work around this problem, eliminate one of the following three
contributing factors:

1. Turn off loop optimization.

-or-

2. Do not use register variables that are referenced in an _asm block.

-or-

3. Compile without /qc.

Microsoft has confirmed this to be a problem in C versions 6.00 and
6.00a and QuickC versions 2.50 and 2.51 (buglist2.50 and buglist2.51).
We are researching this problem and will post new information here as
it becomes available.

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