Hi,
the compiler output message reads a bit confusing. I'm no expert in gcc
internals but as for your code..
Yann Ramin wrote:
The following code produces the following error. It doesn't trigger the error
if the global is not marked volatile. Any ideas?
gcc-current from CVS as of a week ago
gcc-3.4.4
Linux
Code:
volatile uint32_t t;
int main() {
int count;
count = count << 3;
The local variable count is uninitialized and used as rvalue. This is no
syntactical "error" but a semantical one. It leads to undefined results.
uint32_t g = count;
Did you tell your compiler to compile C++ code? In C you cannot
declare/define new local variables inside a block after the first
instructions (you have to omit the preceding line count = count << 3;).
-> This is a syntactical error!
A possible reason for the difference with or without volatile is the
optimization:
The assignment of t is the last executed line of code. t is not used and
can be optimized away and so can the last line. As a next step you can
see that if you omit the last line g is not used anywhere else and thus
can be optimized away. (Finally for the same reason also count can be
omitted and main() is ... empty).
The situation differs if you plan to access t from out of main's control
flow (i.e. from an ISR). In this case all the other lines are needed
too. You use volatile to inform the compiler about this very fact.
Regards
Arnd-Hendrik
t = g | t;
}
Error:
msp430-gcc -g -mmcu=msp430x1611 -o main main.c
main.c: In function `main':
main.c:61: error: unrecognizable insn:
(insn 75 74 28 0 main.c:27 (set:HI (subreg:HI (mem/v/f:SI (symbol_ref:HI ("t")
<var_decl 0xb7cfbaf8 t>) [0 t+0 S4 A16]) 2)
(ior:HI (subreg:HI (mem/v/f:SI (symbol_ref:HI ("t") <var_decl
0xb7cfbaf8 t>) [0 t+0 S4 A16]) 2)
(mem/f:HI (plus:HI (reg/f:HI 4 r4)
(const_int 4 [0x4])) [0 g+2 S2 A16]))) -1 (nil)
(nil))
main.c:61: internal compiler error: in extract_insn, at recog.c:2083
Please submit a full bug report,
with preprocessed source if appropriate.
See <URL:http://gcc.gnu.org/bugs.html> for instructions.
make: *** [main] Error 1
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