Richard Sandiford <[EMAIL PROTECTED]> writes:
> David Daney <[EMAIL PROTECTED]> writes:
>> For r131631 bootstrap on mipsel-linux in stage2 I am getting:
>>
>> [...]
>> ../../trunk/gcc/global.c:1020: error: array subscript is above array bounds
>> make[3]: *** [global.o] Error 1
>>
>> This is new since r131576:
>>
>> http://gcc.gnu.org/ml/gcc-testresults/2008-01/msg00758.html
>>
>> The configuration is identical to that successful bootstrap/test
>
> global.c:1020 is new code that was added during that time. There's
> nothing intrinsically wrong with it though. The warning is simply about
> something that can't prove is dead code. (I.e. it's another example in
> favour of Mark's "the middle end shouldn't warn" thing.) A reduced
> testcase is:
>
> ----------------------------------------------------------------------
> #define BIT(X, B) ((X) < ((B) ? 2 : 4) ? (X) + 4 : ~0U)
>
> void bar (unsigned int *);
> void foo (unsigned int b)
> {
> unsigned int i, a[4];
>
> for (i = 0; BIT (i, b) != ~0U; i++)
> a[BIT (i, b) / 32] |= 1U << (BIT (i, b) % 32);
> bar (a);
> }
> ----------------------------------------------------------------------
>
> which generates a warning on x86_64-linux-gnu when compiled with -O2 -Wall.
> We generate array accesses for a[(i + 4) / 32] and a[~0U / 32] and can't
> prove that the latter are never used.
>
> The attached patch uses the same construct as other E_R_D_R loops
> and avoids the warning. I'll test it overnight and install as obvious
> if it succeeds.
Bootstrapped & regression-tested on x86_64-linux-gnu. Tested also
by building mips64-linux-gnu (with --enable-werror and an equivalent
x86_64 CC, as usual). Installed with this change log:
gcc/
* global.c (find_reg): Only compute EH_RETURN_DATA_REGNO once per
input.
> Index: gcc/global.c
> ===================================================================
> --- gcc/global.c 2008-01-19 23:54:32.000000000 +0000
> +++ gcc/global.c 2008-01-19 23:54:56.000000000 +0000
> @@ -1016,8 +1016,13 @@ find_reg (int num, HARD_REG_SET losers,
> if (allocno[num].no_eh_reg)
> {
> unsigned int j;
> - for (j = 0; EH_RETURN_DATA_REGNO (j) != INVALID_REGNUM; j++)
> - SET_HARD_REG_BIT (used1, EH_RETURN_DATA_REGNO (j));
> + for (j = 0; ; ++j)
> + {
> + unsigned int regno = EH_RETURN_DATA_REGNO (j);
> + if (regno == INVALID_REGNUM)
> + break;
> + SET_HARD_REG_BIT (used1, regno);
> + }
> }
> #endif
>
