Hi!
When working on PR57130, I've wondered why we don't simplify it much earlier
and end up with creating such weirdness.
The following patch fixes that, by using nonzero_bits to see if all the low
bits must be zero and in that case just return zero.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2013-05-02 Jakub Jelinek <ja...@redhat.com>
* simplify-rtx.c (simplify_truncation): If nonzero_bits
on op shows all bits zero in mode, return zero.
--- gcc/simplify-rtx.c.jj 2013-04-03 15:46:45.000000000 +0200
+++ gcc/simplify-rtx.c 2013-05-02 11:16:18.202043607 +0200
@@ -774,6 +774,11 @@ simplify_truncation (enum machine_mode m
return simplify_gen_unary (TRUNCATE, mode, XEXP (op, 0),
GET_MODE (XEXP (op, 0)));
+ /* If op is known to have all lower bits zero, the result is zero. */
+ if (HWI_COMPUTABLE_MODE_P (op_mode)
+ && (nonzero_bits (op, op_mode) & GET_MODE_MASK (mode)) == 0)
+ return CONST0_RTX (mode);
+
return NULL_RTX;
}
Jakub
