[Top] [All Lists]

register declared variable for no optimization

Subject: register declared variable for no optimization
From: Long Li <>
Date: Thu, 30 Jan 2003 15:11:19 -0800 (PST)
Original-recipient: rfc822;

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!



Do you Yahoo!?
Yahoo! Mail Plus - Powerful. Affordable. Sign up now.

<Prev in Thread] Current Thread [Next in Thread>