Re: How can I get VRP information for an RTX?

[David Daney <ddaney at avtrex dot com>]

Andrew Haley wrote:
> Andrew Pinski writes:
>  > It seems wrong that the java front-end thinks we don't have to use
>  > the divide subroutine for MIPS.  Really I think it is wrong that
>  > the mips back-end thinks it should enable by default trap on divide
>  > by zero.
>
> I'm not sure about that: the MIPS conditional trap instruction is
> quite efficient.  Before making any change we should do some
> benchmarking.

There are two issues:

1) Should the compiler generate a trap on division by zero?

As far as I can tell, most mips compilers can be configured to generate 
a trap on division by zero.  We should not remove this capability, just 
make it as efficient as possible.

2) Should the mips[el]-linux port of libgcj use trapping division?

The JLS requires that an exception be thrown on division by zero.  For 
the mips a division + conditional trap = 2 instructions and no 
branching.  Calling the special libgcj divide function executes at least 
4 times as many instructions and involves at least two jumps (call and 
return).  I am not going to benchmark it.  If you think there is a 
better way, you can benchmark it and report your findings.

David Daney