I noticed this while looking at dependency violations that occur during a gcc
bootstrap. We get two in the libgcc build, both are due to the same problem.
Here is a testcase extracted from libgcc/soft-float/fixunstfti.c.
int
sub (int i)
{
float tmp;
if (i)
__asm__ __volatile__ ("frcpa.s0 %0,p1=f0,f0" \
: "=f" (tmp) : : "p1" ); \
return i + 10;
}
Compiling this with -O2 gives a DV error because there is a missing stop bit
after the asm. The assembler code has
#APP
// 6 "tmp.c" 1
frcpa.s0 f6,p1=f0,f0
// 0 "" 2
#NO_APP
.L2:
.mib
adds r8 = 10, r32
mov pr = r2, -1
br.ret.sptk.many b0
The problem is in rtx_needs_barrier in config/ia64/ia64.c, which has
case CLOBBER:
case USE:
/* Clobber & use are for earlier compiler-phases only. */
break;
I think this was written in the olden days when we still had reg-no-conflict
blocks and libcall blocks and other stuff that would insert naked clobbers into
the rtl stream. These should be ignored, but I don't think that they will
occur anymore. However, it isn't safe to ignore a clobber inside a parallel,
particularly when that parallel is for an extended asm. This is a serious
problem that needs to be fixed.
The problem can be worked around by using -mvolatile-asm-stop, but this
obviously only works for volatile asms.
--
Summary: IA-64 asm clobbers are ignored
Product: gcc
Version: 4.5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: wilson at gcc dot gnu dot org
GCC target triplet: ia64-*
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43897
