Re: register declared variable for no optimization
If I remember correct the register keyword is an advise to the
compiler that the variable will be used heavy not that the compiler
always should use a register.
Anyway I think the GCC people can help you on this one.
> I have a question on the GCC optimization. I am using
> GCC3.0.4 MIPS crosscompiler on Redhat 7.1. In a
> function I did the following:
> register unsigned int temp;
> temp = devict.dev1.devtc
> I compiled the code with optimization level 0 and
> found something weird about the register variable
> temp. This is shows in the disassembly file:
> for temp = devict.dev1.devtc
> lui $3, 0xb801
> lw $3, 28($3)
> This is right since the CPU loads the
> devict.dev1.devtc value from memory to the register 3.
> However, after the above instructions, I found:
> sw $3, 0($30)
> lw $2, 0($30)
> now the compiler asked the CPU to store the register
> in the stack. However, I declared the variable as a
> register, how come it still needs to go to the stack?
> I compiled the same code with gcc-2.8.1, optimization
> level 0, and did not find the same issue there.
> Why the gcc-3.0.4 did the weird stuff? Do I have to
> use at least level 1 to make the register declared
> work for it?
> Thanks a lot!
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