Re: odd internal failure

[David Malcolm <dmalcolm@redhat.com>]

On Thu, 2021-12-02 at 12:40 +0100, Richard Biener via Gcc wrote:
> On Wed, Dec 1, 2021 at 9:56 PM Gary Oblock <gary@amperecomputing.com>
> wrote:
> > 
> > Richard,
> > 
> > I rebuilt at "-O0" and that particular call now works but on a call
> > to
> > the same function with a different offset it fails. 😱
> 
> use a debugger to see why

In case you haven't seen them, I put together some tips on debugging
GCC here:
https://dmalcolm.fedorapeople.org/gcc/newbies-guide/debugging.html
https://github.com/davidmalcolm/gcc-newbies-guide/blob/master/debugging.rst

Inserting print statements only gets you so far; at some point you
really need a debugger.

Dave

> 
> > Thanks,
> > 
> > Gary
> > 
> > 
> > ________________________________
> > From: Richard Biener <richard.guenther@gmail.com>
> > Sent: Wednesday, December 1, 2021 1:09 AM
> > To: Gary Oblock <gary@amperecomputing.com>
> > Cc: gcc@gcc.gnu.org <gcc@gcc.gnu.org>
> > Subject: Re: odd internal failure
> > 
> > [EXTERNAL EMAIL NOTICE: This email originated from an external
> > sender. Please be mindful of safe email handling and proprietary
> > information protection practices.]
> > 
> > 
> > On Wed, Dec 1, 2021 at 8:46 AM Gary Oblock via Gcc <gcc@gcc.gnu.org>
> > wrote:
> > > 
> > > What is happening should be trivial to determine but for some
> > > reason it's
> > > not. I'd normally bounce this off a coworker but given the pandemic
> > > and modern dispersed hiring practices it's not even remotely
> > > possible.
> > > 
> > > I'm making this call and tree_to_uhwi is failing on an internal
> > > error.
> > > That's normally easy to fix, but here is where the weirdness kicks
> > > in.
> > > 
> > >   unsigned HOST_WIDE_INT wi_offset = tree_to_uhwi (offset);
> > > 
> > > tree_to_uhwi from tree.h is:
> > > 
> > > extern inline __attribute__ ((__gnu_inline__)) unsigned
> > > HOST_WIDE_INT
> > > tree_to_uhwi (const_tree t)
> > > {
> > >   gcc_assert (tree_fits_uhwi_p (t));
> > >   return TREE_INT_CST_LOW (t);
> > > }
> > > 
> > > and
> > > 
> > > tree_fits_uhwi_p from tree.c is
> > > 
> > > bool
> > > tree_fits_uhwi_p (const_tree t)
> > > {
> > >   return (t != NULL_TREE
> > >  && TREE_CODE (t) == INTEGER_CST
> > >  && wi::fits_uhwi_p (wi::to_widest (t)));
> > > }
> > > 
> > > Here's what this instrumentation shows (DEBUG_A is an indenting
> > > fprintf to
> > > stderr.)
> > > 
> > >   DEBUG_A ("TREE_CODE(offset) = %s  && ", code_str (TREE_CODE
> > > (offset)));
> > >   DEBUG_A ("fits %s\n", wi::fits_uhwi_p (wi::to_widest (offset)) ?
> > > "true" : "false");
> > >   DEBUG_A ("tree_fits_uhwi_p(offset) %s\n",tree_fits_uhwi_p
> > > (offset) ? "true" : "false");
> > > 
> > >            TREE_CODE(offset) = INTEGER_CST  && fits true
> > >            tree_fits_uhwi_p(offset) true
> > > 
> > > By the way, offset is:
> > > 
> > > _Literal (struct BASKET * *) 8
> > > 
> > > And it's an operand of:
> > > 
> > > MEM[(struct BASKET * *)&perm + 8B]
> > > 
> > > Any clues on what's going on here?
> > 
> > it should just work.
> > 
> > > Thanks,
> > > 
> > > Gary
> > > 
> > 
> > Btw, try to setup things so you don't spam below stuff to public
> > mailing lists.
> > 
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