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Re: Fold constant shifts in combine
- From: John David Anglin <dave at hiauly3 dot hia dot nrc dot ca>
- To: gcc-patches at gcc dot gnu dot org
- Cc: jh at suse dot cz, rth at redhat dot com
- Date: Mon, 24 Feb 2003 01:23:18 -0500 (EST)
- Subject: Re: Fold constant shifts in combine
This patch causes the following code to be miscompiled:
Wed Feb 19 18:45:45 CET 2003 Jan Hubicka <jh at suse dot cz>
* combine.c (simplify_shift_const): Simplify few special cases
into constants.
#define GET_FIELD(X, FROM, TO) \
((X) >> (31 - (TO)) & ((1 << ((TO) - (FROM) + 1)) - 1))
#define SIGN_EXTEND(VAL,BITS) \
((int) ((VAL) >> ((BITS) - 1) ? (-1 << (BITS)) | (VAL) : (VAL)))
unsigned int *
foo (unsigned int val)
{
unsigned int *p = (unsigned int *) 0x4000c51c;
p += SIGN_EXTEND (GET_FIELD (val, 19, 28) |
GET_FIELD (val, 29, 29) << 10 |
GET_FIELD (val, 11, 15) << 11 |
GET_FIELD (val, 31, 31) << 16, 17);
return p;
}
int
main ()
{
printf ("p = 0x%x\n", foo (0xe85f1845));
exit (0);
}
The sign extension is not handled correctly.
Dave