Re: [Bug target/11156] New: new bootstrap failure on mips-sgi-irix6.5 stage2 libgcc2 fp-bit.c

[Richard Sandiford <rsandifo at redhat dot com>]

"ghazi@gcc.gnu.org" <gcc-bugzilla@gcc.gnu.org> writes:
> PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.
> Sometime between June 7 and June 8, I started getting a new bootstrap failure 
> on mainline for mips-sgi-irix6.5 in stage2 building libgcc2.  It looks like 
> this:
> 
> fp-bit.c: In function `__pack_f':
> fp-bit.c:205: internal compiler error: Segmentation fault
> Please submit a full bug report,
> with preprocessed source if appropriate.
> See <URL:http://gcc.gnu.org/bugs.html> for instructions.
> make[3]: *** [libgcc/./_pack_sf.o] Error 1

Ah, so it _isn't_ just me ;)

I believe it's a bug in the native irix assembler.  In fold(),
we have the code:

        .set    noreorder
        .set    nomacro
        bne     $2,$0,.L3414
        move    $6,$2
        .set    macro
        .set    reorder

which gets assembled as:

   2caf4:       10400004        beqz    v0,2cb08 <.LCFI407+0x184fc>
   2caf8:       8f810001        lw      at,1(gp)
                        2caf8: R_MIPS_GOT16     .text+0x14fd0
   2cafc:       24214fd0        addiu   at,at,20432
                        2cafc: R_MIPS_LO16      .text
   2cb00:       00200008        jr      at
   2cb04:       00000000        nop
   2cb08:       00403025        move    a2,v0

In other words, the bne has been changed into a long branch sequence,

I'm suprised the assembler does this for branches inside a set
noreorer/set nomacro block, especially given that the original
branch _was_ within range.

Anyway, the problem is that delay slot insn is now only executed
when the branch isn't taken.

I'm not sure what's triggered it.  It might be the recent growth in
fold(), or it might be related to the 'label in delay slot' problem
that was seen on sparc (the irix assembler warns about the same thing).
But whatever caused it, it's still a bug in the assembler.

Richard