Re: Condition branch on least significant bit

["Jan Hoogerbrugge" <hoogerbrugge at hotmail dot com>]

Hi Richard,

> From: Richard Henderson <rth@redhat.com>
> > Any idea how to deal with this problem?
>
> Michael's BImode suggestion is most correct for the common case:
> emit BImode compare and then branch.

I followed your and Michael's suggestion (thank you) and that seems to 
work.... almost. The problem is that I have a benchmark where gcc keeps on 
looping in reload1.c:

                     enum machine_mode narrow_mode;
                     for (narrow_mode = GET_CLASS_NARROWEST_MODE 
(MODE_INT);
                          narrow_mode != GET_MODE (reg);
                          narrow_mode = GET_MODE_WIDER_MODE (narrow_mode))
                       {
                         if (have_insn_for (STRICT_LOW_PART, narrow_mode)
                         ...
                       }

This code loops over all integer modes starting with the smallest one which 
happens to be QImode. In the case that gcc loops forever, reg is BImode and 
therefore the loop never terminates. What is wrong?

- Is it that have_insn_for (STRICT_LOW_PART, narrow_mode) is always false? 
If so, how to fix this?
- Is it that the termination condition of the loop is not correct. I see 
many of these loops in gcc where mode != VOIDmode is the termination 
condition?
- Should GET_CLASS_NARROWEST_MODE (MODE_INT) return BImode instead of SImode 
which it currently seems to do?

Cheers,
Jan

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