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df: Fix up handling of paradoxical subregs in debug insns [PR101170] 

The recent addition of gcc_assert (regno < endregno); triggers during
glibc build on m68k.
The problem is that RA decisions shouldn't depend on expressions in
DEBUG_INSNs and those expressions can contain paradoxical subregs of certain
pseudos.  If RA then decides to allocate the pseudo to a register
with very small hard register REGNO, we can trigger the new assert,
as (int) subreg_regno_offset may be negative on big endian and the small
REGNO + the negative offset can wrap around.

The following patch in that case records the range from the REGNO 0 to
endregno, before the addition of the assert as both regno and endregno are
unsigned it wouldn't record anything at all silently.

2021-06-24  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/101170
	* df-scan.c (df_ref_record): For paradoxical big-endian SUBREGs
	where regno + subreg_regno_offset wraps around use 0 as starting
	regno.

	* gcc.dg/pr101170.c: New test.
This commit is contained in:
Jakub Jelinek 2021-06-24 12:24:48 +02:00
parent 65371066d8
commit 9872bd8c35
2 changed files with 52 additions and 3 deletions
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18
gcc/df-scan.c
View File

@ -2576,9 +2576,21 @@ df_ref_record (enum df_ref_class cl,
if (GET_CODE (reg) == SUBREG)
{
regno += subreg_regno_offset (regno, GET_MODE (SUBREG_REG (reg)),
SUBREG_BYTE (reg), GET_MODE (reg));
endregno = regno + subreg_nregs (reg);
int off = subreg_regno_offset (regno, GET_MODE (SUBREG_REG (reg)),
SUBREG_BYTE (reg), GET_MODE (reg));
unsigned int nregno = regno + off;
endregno = nregno + subreg_nregs (reg);
if (off < 0 && regno < (unsigned) -off)
/* Deal with paradoxical SUBREGs on big endian where
in debug insns the hard reg number might be smaller
than -off, such as (subreg:DI (reg:SI 0 [+4 ]) 0));
RA decisions shouldn't be affected by debug insns
and so RA can decide to put pseudo into a hard reg
with small REGNO, even when it is referenced in
a paradoxical SUBREG in a debug insn. */
regno = 0;
else
regno = nregno;
}
else
endregno = END_REGNO (reg);

37
gcc/testsuite/gcc.dg/pr101170.c Normal file
View File

@ -0,0 +1,37 @@
/* PR middle-end/101170 */
/* { dg-do compile } */
/* { dg-options "-O2 -g" } */
#include <stdarg.h>
struct S { int a; int b[4]; } s;
va_list ap;
int i;
long long l;
struct S
foo (int x)
{
struct S a = {};
do
if (x)
return a;
while (1);
}
__attribute__((noipa)) void
bar (void)
{
for (; i; i++)
l |= va_arg (ap, long long) << s.b[i];
if (l)
foo (l);
}
void
baz (int v, ...)
{
va_start (ap, v);
bar ();
va_end (ap);
}