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Re: gcc 4.3.0 i386 default question

Richard Guenther wrote:
On Wed, Mar 12, 2008 at 4:23 PM, Joel Sherrill
<> wrote:

 Did the default i386 CPU model that gcc generates
 code for change between 4.2.x and 4.3.0?  I didn't
 see anything in the release notes that jumps out at
 me about this.

 Using i386-rtems4.9 as the target, I was running
 code compiled by gcc 4.3.0 on a  vanilla i386 and
 was getting illegal instruction  exceptions.  I looked
 at the assembly and noticed instructions which were
 not on the i386.  Obviosuly, when I added -mtune=i386
 and the issue went away.

This probably impacts no one on a GNU/Linux computer
since very few of those are base i386's anymore. Just
venerable embedded systems. :)

-mtune doesn't change the instruction set, -march/-mcpu does.
So this is probably a bug in the instruction predicates. What
is the illegal instruction gcc emits?
I saw a series of instructions with something like
mm0 as a register.  I can't duplicate it now but
also realized that a background automated run
of tests may have been replacing the boot image
behind my back. <sigh>  The danger of multitasking.

I am sorry to have raised this.  I think this points out
what is happening in the failures I see when running
the gcc testsuite though:

Lots of tests with "vect" or "sse" in the name fail when run
on the same vanilla i386 target.  For example,
gcc.dg/vect/costmodel/i386/costmodel-vect-31.c fails with
a similar illegal instruction exception.  Looking at that particular
case, I see that it is compiled with -msse2 and fails with an
illegal instruction exception when it tries this one:

10022a: f2 0f 10 c0 movsd %xmm0,%xmm0

Is there any way to skip these tests for particular HW features
that are not present?  There are similar failures on the PowerPC
target I use for reporting because it doesn't have Altivec.

Thanks. Sorry for the bogus question.


Joel Sherrill, Ph.D.             Director of Research & Development        On-Line Applications Research
Ask me about RTEMS: a free RTOS  Huntsville AL 35805
  Support Available             (256) 722-9985

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