Messages in this thread | | | Date | Tue, 13 Nov 2007 11:36:00 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [patch 5/8] Immediate Values - x86 Optimization |
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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". > > 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" ? >
For "char" (8-bit) values, sp/bp/si/di are illegal in 32-bit mode.
Hence "=q".
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