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Re: Errors building libgcc for powerpc64le-linux-gnu

On Sun, Dec 15, 2019 at 09:43:20AM -0800, Ian Lance Taylor wrote:
> On Sat, Dec 14, 2019 at 11:25 PM Segher Boessenkool
> <> wrote:
> >
> > On Sat, Dec 14, 2019 at 10:51:50AM -0800, Ian Lance Taylor via gcc wrote:
> > > I'm seeing compiler crashes building libgcc for powerpc64le-linux-gnu,
> > > cross-compiling from x86_64-pc-linux-gnu.  I'm at SVN revision 279830.
> > > I'm seeing the following.  Is anybody else seeing this crash?  Thanks.
> >
> > No, and that makes me wonder what is going on.  The error is simple enough
> > of course, as you note in a later message; but why do we not see it on
> > every other build?
> I think it's because clang treats a left shift by a negative number as
> undefined behavior but GCC does not.  So GCC is consistently producing
> some number, and clang is producing different numbers.

Hrm.  Why did that not show up with ubsan then though?  (Or maybe it did,
and I just never heard).

> I should note that I don't really understand what purpose that
> constant is serving anyhow.

-  "operands[2] = GEN_INT (1 << (75 - REGNO (operands[0])));")
+  "operands[2] = GEN_INT (1 << (7 - (REGNO (operands[0]) - CR0_REGNO)));")

The constant is the bitmask of which CR fields to save/restore (always
one here, but the insn allows any combination).

Committing that patch later today.  Thanks for the report!


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