Re: [patch 5/8] Immediate Values - x86 Optimization

Mathieu Desnoyers
2007-11-13T19:24:56Z

* H. Peter Anvin (hpa@zytor.com) wrote:
> Mathieu Desnoyers wrote:
> - Use "=g" constraint for char immediate value inline assembly.
>
> "=g" is the same as "=rmi" which is inherently bogus. In your actual code
> you use "=r", the correct constraint is "=q".
>

Hi Peter,

Yup, =g wasn't what I was looking for at all, the header comment is
bogus.

From
http://gcc.gnu.org/onlinedocs/gcc/Simple-Constraints.html#Simple-Constraints

`r'
A register operand is allowed provided that it is in a general register.

From
http://gcc.gnu.org/onlinedocs/gcc/Machine-Constraints.html#Machine-Constraints
Intel 386 config/i386/constraints.md

q
Any register accessible as rl. In 32-bit mode, a, b, c, and d; in 64-bit mode, any integer register.

I am worried that "=q" might exclude the si and di registers in 32-bit mode.

What exactly is wrong with "=r" ?

> -hpa