[patches] Re: reversing of FP conditions infrastructure

[Richard Henderson]

On Sun, Jan 07, 2001 at 07:17:47PM +0100, Jan Hubicka wrote:
> Take i386 as an example - we do have better instructions for trapping
> compares than for non-trapping compares (fcom takes memory argument,
> unlike fucom ...

Interesting point.  I'd forgotten about the fucom/fcom/fcomi asymmetry.

> Then the pattern will just refuse the cases it can't handle directly.
> Generic code should always behave in a way to verify that instruciton
> is valid after the transformation ...

Yes, it should.  But jump.c is infamous for not doing this.

Clean this up, and we can canonicalize jumps to have the label only in
the "then" slot of the if_then_else.  Which allows us to clean up quite
a lot of the rest of the compiler.  Many of the existing reversals go
away, in fact.

I guess I need to think about this some more.



r~