Consider
a = (x / 39) * 32 + (x % 39)
If we have no instruction to produce both the quotient and the remaineder, this
can be computed as
y = x / 39
z = x - y * 39
a = y * 32 + z
The last line can be simplified by substituting:
a = y * 32 + x - y * 39
a = y * (32 - 39) + x
a = x - y * 7
Testcase:
int i_size;
extern void foo (void);
int udf_check_anchor_block(int block)
{
i_size = ( ( ( (block) / 39 ) << 5 ) + ( block % 39 ));
return 1;
}
The tree optimization phase misses this, and this PR should stay open until
that is resolved. The combiner can handle it if it is able to look at 4
instructions.
--
Summary: Mathematical simplification missed at tree-level
Product: gcc
Version: 4.6.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: bernds at gcc dot gnu dot org
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45218
