Re: CSE bug when narrowing constants

[Graham Stott <graham dot stott at btinternet dot com>]

All,

One thing that may or may not be related is that the current main
fails to bootstrap on x86_64 with fold checking enabled. 

It aborts due to a fold-checking failure (i.e fold has modified 
it's inputs) using the stage1 compiler. I don't recall exactly which 
file it triggers on (I think it was one of the host-ieee*.c files
in libdecnumber library). 

The last bootstrap I did was about 8 weeks ago and that passed with
all checking enabled so its a *recent* regression.

I'll look into the cause this evening.

Cheers
Graham     


--- On Mon, 1/12/08, Eric Botcazou <ebotcazou@adacore.com> wrote:

> From: Eric Botcazou <ebotcazou@adacore.com>
> Subject: Re: CSE bug when narrowing constants
> To: "Gary Funck" <gary@intrepid.com>
> Cc: gcc@gcc.gnu.org
> Date: Monday, 1 December, 2008, 10:50 AM
> > cse_insn() calls lookup_as_function() ultimately
> through fold_rtx(), IIRC,
> > and is the routine that writes the REG_EQUAL note.
> 
> OK, thanks.  But I'm a little at a loss as to why this
> problem arises only
> now: the problematic code in lookup_as_function is one
> decade old.  Do you 
> happen to have older compilers around (say GCC 4.1.x based)
> that correctly 
> compile the testcase?  If so, what happens differently with
> them?
> 
> -- 
> Eric Botcazou