Messages in this thread | | | Date | Tue, 18 Sep 2007 14:51:18 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: [patch 4/7] Immediate Values - i386 Optimization |
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Mathieu Desnoyers wrote:
> +#define immediate_read(name) \ > + ({ \ > + __typeof__(name##__immediate) value; \ > + switch (sizeof(value)) { \ > + case 1: \ > + asm ( ".section __immediate, \"a\", @progbits;\n\t" \ > + ".long %1, (0f)+1, 1;\n\t" \ > + ".previous;\n\t" \ > + "0:\n\t" \ > + "mov %2,%0;\n\t" \
Given that you're relying on the exact instruction that this mov generates, it might be better to explicitly put the opcodes in with .byte. That way you're protected from the assembler deciding to generate some other form of the instruction (for whatever reason). I guess substituting in different registers would be a pain.
Aside from that, is there any reason not to just put $0 in there rather than use %2?
> + ".long %1, (0f)+1, 4;\n\t" \ > + ".previous;\n\t" \ > + "1:\n\t" \ > + ".org (1b)+(3-((1b)%%4)), 0x90;\n\t" \ > Seems a little complex, but I couldn't come up with anything much better:
.org . + 3 - (. & 3), 0x90
You can use . rather than needing to define 1:, it doesn't need quite so many parens, and using &3 avoids the %% wart.
It's a pity that gas seems to generate plain 0x90 nops rather than long-nop forms here. I thought it could do that.
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