Hi all,
I am facing with a GCSE problem on this GCC
testsuite(gcc/testsuite/gcc.c-torture/execute/pr38819.c),using
GCC-4.4.0:
----------------------------------------
extern void exit (int);
extern void abort (void);
volatile int a = 1;
volatile int b = 0;
volatile int x = 2;
volatile signed int r = 8;
void __attribute__((noinline))
foo (void)
{
exit (0);
}
int
main (void)
{
int si1 = a;
int si2 = b;
int i;
for (i = 0; i < 100; ++i) {
foo ();
if (x == 8)
i++;
r += i + si1 % si2;
}
abort ();
}
----------------------------------------
On the mips64 architecture,instruction for si1%si2(that is,div) will
put the result in LO and HI,and thus GCC don't want to do GCSE
optimization on this instruction(see gcc/gcse.c:want_to_gcse_p()).
But now I am facing with a new instruction which will put the result
in a single register,and thus GCC want to do GCSE on this
instruction.GCC will treat si1%si2 as a loop invariant.So si1%si2 was
moved out of the loop,just before the execution of function foo();as
si2 is equal 0,there occurs a trap which shouldn't have occurred
according to the original semantic.
I am considering a solution:in a certain basic block,if there
exists a function call rtx(which might exit or even trap in
advance),then we shall not do GCSE optimization on the following rtx
which might trap(see rtlanal.c:may_trap_p()).But it seems the cost is
expensive,and I am not quite sure whether or not it works.
So,does anyone have any suggestions?
Thanks in advance.
