On 09/20/2009 06:31 PM, Richard Guenther wrote:
On Sun, Sep 20, 2009 at 6:10 PM, Andreas Schwab<sch...@linux-m68k.org> wrote:
Why is postreload converting (set (REGX) (CONST_INT A)) ... (set (REGX)
(CONST_INT B)) into (set (STRICT_LOW_PART (REGX)) (CONST_INT B))? That
looks like a pessimisation especially if the constants are small, since
STRICT_LOW_PART must not touch the high part. Is there a way for the
backend to stop postreload from doing this if the constants are in some
range? On the m68k, loading a constant in the range -128..127 in SI
mode is better than loading it in strict QI mode.
It's probably an omission of a check if A& ~GET_MODE_MASK (narrow_mode)
is equal to zero.
Actually it is (A^B) & ~GET_MODE_MASK(narrow_mode) that has to be 0.
And of course a cost check is completely missing.
I think that adding a cost check would be the right thing to do. For
size, a QImode move is probably better (it is on i386 for example).
Paolo
