PR90723

Hi,
For following test-case:

typedef double v4df __attribute__ ((vector_size (32)));
void foo(v4df);

int
main ()
{
  volatile v4df x1;
  x1 = (v4df) { 10.0, 20.0, 30.0, 40.0 };
  foo (x1);
  return 0;
}

Compiling with -msve-vector-bits=256, the compiler goes into infinite
recursion and eventually segfaults due to stack overflow.

This happens during expansion of:
  x1.0_1 ={v} x1;

aarch64_expand_sve_mem_move calls aarch64_emit_sve_pred_move with
dest = (reg:VNx2DF 93) and
src = (mem/u/c:VNx2DF
           (plus:DI (reg/f:DI 94) (const_int 32 [0x20])) [0  S32 A128])

aarch64_emit_sve_pred_move calls expand_insn with above ops.
Eventually we hit EXPAND_INPUT case in maybe_legitimize_operand for
src (opno == 2)

Since the operand is marked with volatile, and volatile_ok is set to false,
insn_operand_matches return false and we call:
      op->value = copy_to_mode_reg (mode, op->value);
      break;

copy_to_mode_reg however, creates a fresh register and calls emit_move_insn:
rtx temp = gen_reg_rtx (mode);
if (x != temp)
    emit_move_insn (temp, x);

and we again end up in aarch64_emit_sve_pred_move, with dest assigned
the new register and src remaining unchanged, and thus the cycle continues.

As suggested by Richard, the attached patch temporarily sets volatile_ok to true
using RAII class volatile_ok_temp in aarch64_emit_sve_pred_move which
avoids the recursion.

Bootstrap + tested on x86_64-unknown-linux-gnu, aarch64-linux-gnu.
Cross-testing with SVE in progress.
OK to commit ?

Thanks,
Prathamesh
2019-07-09  Prathamesh Kulkarni  <prathamesh.kulkarni@linaro.org>

	PR target/90723
	* recog.h (volatile_ok_temp): New class.
	* config/aarch64/aarch64.c (aarch64_emit_sve_pred_move): Set
	volatile_ok temporarily to true using volatile_ok_temp.
	* expr.c (emit_block_move_via_cpymem): Likewise.
	* optabs.c (maybe_legitimize_operand): Likewise.

Prathamesh Kulkarni <prathamesh.kulkarni@linaro.org> writes:
> Hi,
> For following test-case:
>
> typedef double v4df __attribute__ ((vector_size (32)));
> void foo(v4df);
>
> int
> main ()
> {
>   volatile v4df x1;
>   x1 = (v4df) { 10.0, 20.0, 30.0, 40.0 };
>   foo (x1);
>   return 0;
> }
>
> Compiling with -msve-vector-bits=256, the compiler goes into infinite
> recursion and eventually segfaults due to stack overflow.
>
> This happens during expansion of:
>   x1.0_1 ={v} x1;
>
> aarch64_expand_sve_mem_move calls aarch64_emit_sve_pred_move with
> dest = (reg:VNx2DF 93) and
> src = (mem/u/c:VNx2DF
>            (plus:DI (reg/f:DI 94) (const_int 32 [0x20])) [0  S32 A128])
>
> aarch64_emit_sve_pred_move calls expand_insn with above ops.
> Eventually we hit EXPAND_INPUT case in maybe_legitimize_operand for
> src (opno == 2)
>
> Since the operand is marked with volatile, and volatile_ok is set to false,
> insn_operand_matches return false and we call:
>       op->value = copy_to_mode_reg (mode, op->value);
>       break;
>
> copy_to_mode_reg however, creates a fresh register and calls emit_move_insn:
> rtx temp = gen_reg_rtx (mode);
> if (x != temp)
>     emit_move_insn (temp, x);
>
> and we again end up in aarch64_emit_sve_pred_move, with dest assigned
> the new register and src remaining unchanged, and thus the cycle continues.
>
> As suggested by Richard, the attached patch temporarily sets volatile_ok to true
> using RAII class volatile_ok_temp in aarch64_emit_sve_pred_move which
> avoids the recursion.
>
> Bootstrap + tested on x86_64-unknown-linux-gnu, aarch64-linux-gnu.
> Cross-testing with SVE in progress.
> OK to commit ?
>
> Thanks,
> Prathamesh
>
> 2019-07-09  Prathamesh Kulkarni  <prathamesh.kulkarni@linaro.org>
>
> 	PR target/90723
> 	* recog.h (volatile_ok_temp): New class.
> 	* config/aarch64/aarch64.c (aarch64_emit_sve_pred_move): Set
> 	volatile_ok temporarily to true using volatile_ok_temp.
> 	* expr.c (emit_block_move_via_cpymem): Likewise.
> 	* optabs.c (maybe_legitimize_operand): Likewise. 

I'm the last person who should be suggesting names, but how about
temporary_volatile_ok?  Putting "temp" after the name IMO makes it
sound too much like it's describing the RAII object rather than the
value of volatile_ok itself.

> diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
> index 5a923ca006b..50afba1a2b6 100644
> --- a/gcc/config/aarch64/aarch64.c
> +++ b/gcc/config/aarch64/aarch64.c
> @@ -3457,6 +3457,7 @@ aarch64_emit_sve_pred_move (rtx dest, rtx pred, rtx src)
>    create_output_operand (&ops[0], dest, mode);
>    create_input_operand (&ops[1], pred, GET_MODE(pred));
>    create_input_operand (&ops[2], src, mode);
> +  volatile_ok_temp v(true);

Missing space before "(".  Same for later uses.

> [...]
> diff --git a/gcc/recog.h b/gcc/recog.h
> index 75cbbdc10ad..8a8eaf7e0c3 100644
> --- a/gcc/recog.h
> +++ b/gcc/recog.h
> @@ -186,6 +186,22 @@ skip_alternative (const char *p)
>  /* Nonzero means volatile operands are recognized.  */
>  extern int volatile_ok;
>  
> +/* RAII class for temporarily setting volatile_ok.  */
> +
> +class volatile_ok_temp
> +{
> +public:
> +  volatile_ok_temp(int value): save_volatile_ok (volatile_ok)

Missing space before "(" and before ":".

> +  {
> +    volatile_ok = value;
> +  }
> +
> +  ~volatile_ok_temp() { volatile_ok = save_volatile_ok; }

Missing space before "(".

> +
> +private:
> +  int save_volatile_ok;

For extra safety we should probably have a private copy constructor
(declaration only, no implementation).  We're still C++03 and so can't
use "= delete".

Thanks,
Richard


> +};
> +
>  /* Set by constrain_operands to the number of the alternative that
>     matched.  */
>  extern int which_alternative;

On Thu, 11 Jul 2019 at 01:48, Richard Sandiford
<richard.sandiford@arm.com> wrote:
>
> Prathamesh Kulkarni <prathamesh.kulkarni@linaro.org> writes:
> > Hi,
> > For following test-case:
> >
> > typedef double v4df __attribute__ ((vector_size (32)));
> > void foo(v4df);
> >
> > int
> > main ()
> > {
> >   volatile v4df x1;
> >   x1 = (v4df) { 10.0, 20.0, 30.0, 40.0 };
> >   foo (x1);
> >   return 0;
> > }
> >
> > Compiling with -msve-vector-bits=256, the compiler goes into infinite
> > recursion and eventually segfaults due to stack overflow.
> >
> > This happens during expansion of:
> >   x1.0_1 ={v} x1;
> >
> > aarch64_expand_sve_mem_move calls aarch64_emit_sve_pred_move with
> > dest = (reg:VNx2DF 93) and
> > src = (mem/u/c:VNx2DF
> >            (plus:DI (reg/f:DI 94) (const_int 32 [0x20])) [0  S32 A128])
> >
> > aarch64_emit_sve_pred_move calls expand_insn with above ops.
> > Eventually we hit EXPAND_INPUT case in maybe_legitimize_operand for
> > src (opno == 2)
> >
> > Since the operand is marked with volatile, and volatile_ok is set to false,
> > insn_operand_matches return false and we call:
> >       op->value = copy_to_mode_reg (mode, op->value);
> >       break;
> >
> > copy_to_mode_reg however, creates a fresh register and calls emit_move_insn:
> > rtx temp = gen_reg_rtx (mode);
> > if (x != temp)
> >     emit_move_insn (temp, x);
> >
> > and we again end up in aarch64_emit_sve_pred_move, with dest assigned
> > the new register and src remaining unchanged, and thus the cycle continues.
> >
> > As suggested by Richard, the attached patch temporarily sets volatile_ok to true
> > using RAII class volatile_ok_temp in aarch64_emit_sve_pred_move which
> > avoids the recursion.
> >
> > Bootstrap + tested on x86_64-unknown-linux-gnu, aarch64-linux-gnu.
> > Cross-testing with SVE in progress.
> > OK to commit ?
> >
> > Thanks,
> > Prathamesh
> >
> > 2019-07-09  Prathamesh Kulkarni  <prathamesh.kulkarni@linaro.org>
> >
> >       PR target/90723
> >       * recog.h (volatile_ok_temp): New class.
> >       * config/aarch64/aarch64.c (aarch64_emit_sve_pred_move): Set
> >       volatile_ok temporarily to true using volatile_ok_temp.
> >       * expr.c (emit_block_move_via_cpymem): Likewise.
> >       * optabs.c (maybe_legitimize_operand): Likewise.
>
> I'm the last person who should be suggesting names, but how about
> temporary_volatile_ok?  Putting "temp" after the name IMO makes it
> sound too much like it's describing the RAII object rather than the
> value of volatile_ok itself.
>
> > diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
> > index 5a923ca006b..50afba1a2b6 100644
> > --- a/gcc/config/aarch64/aarch64.c
> > +++ b/gcc/config/aarch64/aarch64.c
> > @@ -3457,6 +3457,7 @@ aarch64_emit_sve_pred_move (rtx dest, rtx pred, rtx src)
> >    create_output_operand (&ops[0], dest, mode);
> >    create_input_operand (&ops[1], pred, GET_MODE(pred));
> >    create_input_operand (&ops[2], src, mode);
> > +  volatile_ok_temp v(true);
>
> Missing space before "(".  Same for later uses.
>
> > [...]
> > diff --git a/gcc/recog.h b/gcc/recog.h
> > index 75cbbdc10ad..8a8eaf7e0c3 100644
> > --- a/gcc/recog.h
> > +++ b/gcc/recog.h
> > @@ -186,6 +186,22 @@ skip_alternative (const char *p)
> >  /* Nonzero means volatile operands are recognized.  */
> >  extern int volatile_ok;
> >
> > +/* RAII class for temporarily setting volatile_ok.  */
> > +
> > +class volatile_ok_temp
> > +{
> > +public:
> > +  volatile_ok_temp(int value): save_volatile_ok (volatile_ok)
>
> Missing space before "(" and before ":".
>
> > +  {
> > +    volatile_ok = value;
> > +  }
> > +
> > +  ~volatile_ok_temp() { volatile_ok = save_volatile_ok; }
>
> Missing space before "(".
>
> > +
> > +private:
> > +  int save_volatile_ok;
>
> For extra safety we should probably have a private copy constructor
> (declaration only, no implementation).  We're still C++03 and so can't
> use "= delete".
Thanks for the suggestions.
Does the attached version look OK ?

Thanks,
Prathamesh
>
> Thanks,
> Richard
>
>
> > +};
> > +
> >  /* Set by constrain_operands to the number of the alternative that
> >     matched.  */
> >  extern int which_alternative;
2019-07-11  Prathamesh Kulkarni  <prathamesh.kulkarni@linaro.org>

	PR target/90723
	* recog.h (temporary_volatile_ok): New class.
	* config/aarch64/aarch64.c (aarch64_emit_sve_pred_move): Set
	volatile_ok temporarily to true using temporary_volatile_ok.
	* expr.c (emit_block_move_via_cpymem): Likewise.
	* optabs.c (maybe_legitimize_operand): Likewise.

diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 5a923ca006b..abdf4b1c87a 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -3457,6 +3457,7 @@ aarch64_emit_sve_pred_move (rtx dest, rtx pred, rtx src)
   create_output_operand (&ops[0], dest, mode);
   create_input_operand (&ops[1], pred, GET_MODE(pred));
   create_input_operand (&ops[2], src, mode);
+  temporary_volatile_ok v (true);
   expand_insn (code_for_aarch64_pred_mov (mode), 3, ops);
 }
 
diff --git a/gcc/expr.c b/gcc/expr.c
index 4acf250dd3c..795a56d88a6 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -1732,8 +1732,6 @@ emit_block_move_via_cpymem (rtx x, rtx y, rtx size, unsigned int align,
 			    unsigned HOST_WIDE_INT max_size,
 			    unsigned HOST_WIDE_INT probable_max_size)
 {
-  int save_volatile_ok = volatile_ok;
-
   if (expected_align < align)
     expected_align = align;
   if (expected_size != -1)
@@ -1745,7 +1743,7 @@ emit_block_move_via_cpymem (rtx x, rtx y, rtx size, unsigned int align,
     }
 
   /* Since this is a move insn, we don't care about volatility.  */
-  volatile_ok = 1;
+  temporary_volatile_ok v (true);
 
   /* Try the most limited insn first, because there's no point
      including more than one in the machine description unless
@@ -1809,14 +1807,10 @@ emit_block_move_via_cpymem (rtx x, rtx y, rtx size, unsigned int align,
 		create_fixed_operand (&ops[8], NULL);
 	    }
 	  if (maybe_expand_insn (code, nops, ops))
-	    {
-	      volatile_ok = save_volatile_ok;
-	      return true;
-	    }
+	    return true;
 	}
     }
 
-  volatile_ok = save_volatile_ok;
   return false;
 }
 
diff --git a/gcc/optabs.c b/gcc/optabs.c
index 18ca7370917..187a3d3621d 100644
--- a/gcc/optabs.c
+++ b/gcc/optabs.c
@@ -7202,17 +7202,15 @@ maybe_legitimize_operand (enum insn_code icode, unsigned int opno,
 			  struct expand_operand *op)
 {
   machine_mode mode, imode;
-  bool old_volatile_ok, result;
 
   mode = op->mode;
   switch (op->type)
     {
     case EXPAND_FIXED:
-      old_volatile_ok = volatile_ok;
-      volatile_ok = true;
-      result = maybe_legitimize_operand_same_code (icode, opno, op);
-      volatile_ok = old_volatile_ok;
-      return result;
+      {
+	temporary_volatile_ok v (true);
+	return maybe_legitimize_operand_same_code (icode, opno, op);
+      }
 
     case EXPAND_OUTPUT:
       gcc_assert (mode != VOIDmode);
diff --git a/gcc/recog.h b/gcc/recog.h
index 75cbbdc10ad..8a8c9125ff2 100644
--- a/gcc/recog.h
+++ b/gcc/recog.h
@@ -186,6 +186,23 @@ skip_alternative (const char *p)
 /* Nonzero means volatile operands are recognized.  */
 extern int volatile_ok;
 
+/* RAII class for temporarily setting volatile_ok.  */
+
+class temporary_volatile_ok
+{
+public:
+  temporary_volatile_ok (int value): save_volatile_ok (volatile_ok)
+  {
+    volatile_ok = value;
+  }
+
+  ~temporary_volatile_ok () { volatile_ok = save_volatile_ok; }
+
+private:
+  temporary_volatile_ok (const temporary_volatile_ok&);
+  int save_volatile_ok;
+};
+
 /* Set by constrain_operands to the number of the alternative that
    matched.  */
 extern int which_alternative;

Prathamesh Kulkarni <prathamesh.kulkarni@linaro.org> writes:
> @@ -186,6 +186,23 @@ skip_alternative (const char *p)
>  /* Nonzero means volatile operands are recognized.  */
>  extern int volatile_ok;
>  
> +/* RAII class for temporarily setting volatile_ok.  */
> +
> +class temporary_volatile_ok
> +{
> +public:
> +  temporary_volatile_ok (int value): save_volatile_ok (volatile_ok)

Missing space before the ":".

> +  {
> +    volatile_ok = value;
> +  }
> +
> +  ~temporary_volatile_ok () { volatile_ok = save_volatile_ok; }
> +
> +private:
> +  temporary_volatile_ok (const temporary_volatile_ok&);

Missing space before the "&".

OK with those changes, thanks.

Richard


> +  int save_volatile_ok;
> +};
> +
>  /* Set by constrain_operands to the number of the alternative that
>     matched.  */
>  extern int which_alternative;

On Thu, 11 Jul 2019 at 13:39, Richard Sandiford
<richard.sandiford@arm.com> wrote:
>
> Prathamesh Kulkarni <prathamesh.kulkarni@linaro.org> writes:
> > @@ -186,6 +186,23 @@ skip_alternative (const char *p)
> >  /* Nonzero means volatile operands are recognized.  */
> >  extern int volatile_ok;
> >
> > +/* RAII class for temporarily setting volatile_ok.  */
> > +
> > +class temporary_volatile_ok
> > +{
> > +public:
> > +  temporary_volatile_ok (int value): save_volatile_ok (volatile_ok)
>
> Missing space before the ":".
>
> > +  {
> > +    volatile_ok = value;
> > +  }
> > +
> > +  ~temporary_volatile_ok () { volatile_ok = save_volatile_ok; }
> > +
> > +private:
> > +  temporary_volatile_ok (const temporary_volatile_ok&);
>
> Missing space before the "&".
Oops, sorry about that.
>
> OK with those changes, thanks.
Thanks, committed as r273466.

Thanks,
Prathamesh
>
> Richard
>
>
> > +  int save_volatile_ok;
> > +};
> > +
> >  /* Set by constrain_operands to the number of the alternative that
> >     matched.  */
> >  extern int which_alternative;