forwprop: Further fixes for simplify_rotate [PR108440]

  Hi!

As mentioned in the simplify_rotate comment, for e.g.
   ((T) ((T2) X << (Y & (B - 1)))) | ((T) ((T2) X >> ((-Y) & (B - 1))))
we already emit
   X r<< (Y & (B - 1))
as replacement.  This PR is about the
   ((T) ((T2) X << Y)) OP ((T) ((T2) X >> (B - Y)))
   ((T) ((T2) X << (int) Y)) OP ((T) ((T2) X >> (int) (B - Y)))
forms if T2 is wider than T.  Unlike e.g.
   (X << Y) OP (X >> (B - Y))
which is valid just for Y in [1, B - 1], the above 2 forms are actually
valid and do the rotates for Y in [0, B] - for Y 0 the X value is preserved
by the left shift and right logical shift by B adds just zeros (but because
the shift is in wider precision B is still valid shift count), while for
Y equal to B X is preserved through the latter shift and the former adds
just zeros.
Now, it is unclear if we in the middle-end treat rotates with rotate count
equal or larger than precision as UB or not, unlike shifts there are less
reasons to do so, but e.g. expansion of X r<< Y if there is no rotate optab
for the mode is emitted as (X << Y) | (((unsigned) X) >> ((-Y) & (B - 1)))
and so with UB on Y == B.

The following patch does multiple things:
1) for the above 2, asks the ranger if Y could be equal to B and if so,
   instead of using X r<< Y uses X r<< (Y & (B - 1))
2) for the
   ((T) ((T2) X << Y)) | ((T) ((T2) X >> ((-Y) & (B - 1))))
   ((T) ((T2) X << (int) Y)) | ((T) ((T2) X >> (int) ((-Y) & (B - 1))))
   forms that were fixed 2 days ago it only punts if Y might be in the
   [B,B2-1] range but isn't known to be in the
   [0,B][2*B,2*B][3*B,3*B]... range.  Because for Y which is a multiple
   of B but smaller than B2 it acts as a rotate too, left shift provides
   0 and (-Y) & (B - 1) is 0 and so preserves X.  Though, for the cases
   where Y is not known to be in [0,B-1] the patch also uses
   X r<< (Y & (B - 1)) rather than X r<< Y
3) as discussed with Aldy, instead of using global ranger it uses a pass
   specific copy but lazily created on first simplify_rotate that needs it;
   this e.g. handles rotate inside of if body where the guarding condition
   limits the shift count to some range which will not work with the
   global ranger (unless there is some SSA_NAME to attach the range to).

Note, e.g. on x86 X r<< (Y & (B - 1)) and X r<< Y actually emit the
same assembly because rotates work the same even for larger rotate counts,
but that is handled only during combine.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2023-01-19  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/108440
	* tree-ssa-forwprop.cc: Include gimple-range.h.
	(simplify_rotate): For the forms with T2 wider than T and shift counts of
	Y and B - Y add & (B - 1) masking for the rotate count if Y could be equal
	to B.  For the forms with T2 wider than T and shift counts of
	Y and (-Y) & (B - 1), don't punt if range could be [B, B2], but only if
	range doesn't guarantee Y < B or Y = N * B.  If range doesn't guarantee
	Y < B, also add & (B - 1) masking for the rotate count.  Use lazily created
	pass specific ranger instead of get_global_range_query.
	(pass_forwprop::execute): Disable that ranger at the end of pass if it has
	been created.

	* c-c++-common/rotate-10.c: New test.
	* c-c++-common/rotate-11.c: New test.


	Jakub
  

On Thu, 19 Jan 2023, Jakub Jelinek wrote:

> Hi!
> 
> As mentioned in the simplify_rotate comment, for e.g.
>    ((T) ((T2) X << (Y & (B - 1)))) | ((T) ((T2) X >> ((-Y) & (B - 1))))
> we already emit
>    X r<< (Y & (B - 1))
> as replacement.  This PR is about the
>    ((T) ((T2) X << Y)) OP ((T) ((T2) X >> (B - Y)))
>    ((T) ((T2) X << (int) Y)) OP ((T) ((T2) X >> (int) (B - Y)))
> forms if T2 is wider than T.  Unlike e.g.
>    (X << Y) OP (X >> (B - Y))
> which is valid just for Y in [1, B - 1], the above 2 forms are actually
> valid and do the rotates for Y in [0, B] - for Y 0 the X value is preserved
> by the left shift and right logical shift by B adds just zeros (but because
> the shift is in wider precision B is still valid shift count), while for
> Y equal to B X is preserved through the latter shift and the former adds
> just zeros.
> Now, it is unclear if we in the middle-end treat rotates with rotate count
> equal or larger than precision as UB or not, unlike shifts there are less
> reasons to do so, but e.g. expansion of X r<< Y if there is no rotate optab
> for the mode is emitted as (X << Y) | (((unsigned) X) >> ((-Y) & (B - 1)))
> and so with UB on Y == B.
> 
> The following patch does multiple things:
> 1) for the above 2, asks the ranger if Y could be equal to B and if so,
>    instead of using X r<< Y uses X r<< (Y & (B - 1))
> 2) for the
>    ((T) ((T2) X << Y)) | ((T) ((T2) X >> ((-Y) & (B - 1))))
>    ((T) ((T2) X << (int) Y)) | ((T) ((T2) X >> (int) ((-Y) & (B - 1))))
>    forms that were fixed 2 days ago it only punts if Y might be in the
>    [B,B2-1] range but isn't known to be in the
>    [0,B][2*B,2*B][3*B,3*B]... range.  Because for Y which is a multiple
>    of B but smaller than B2 it acts as a rotate too, left shift provides
>    0 and (-Y) & (B - 1) is 0 and so preserves X.  Though, for the cases
>    where Y is not known to be in [0,B-1] the patch also uses
>    X r<< (Y & (B - 1)) rather than X r<< Y
> 3) as discussed with Aldy, instead of using global ranger it uses a pass
>    specific copy but lazily created on first simplify_rotate that needs it;
>    this e.g. handles rotate inside of if body where the guarding condition
>    limits the shift count to some range which will not work with the
>    global ranger (unless there is some SSA_NAME to attach the range to).
> 
> Note, e.g. on x86 X r<< (Y & (B - 1)) and X r<< Y actually emit the
> same assembly because rotates work the same even for larger rotate counts,
> but that is handled only during combine.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

OK.

Thanks
Richard.

> 2023-01-19  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR tree-optimization/108440
> 	* tree-ssa-forwprop.cc: Include gimple-range.h.
> 	(simplify_rotate): For the forms with T2 wider than T and shift counts of
> 	Y and B - Y add & (B - 1) masking for the rotate count if Y could be equal
> 	to B.  For the forms with T2 wider than T and shift counts of
> 	Y and (-Y) & (B - 1), don't punt if range could be [B, B2], but only if
> 	range doesn't guarantee Y < B or Y = N * B.  If range doesn't guarantee
> 	Y < B, also add & (B - 1) masking for the rotate count.  Use lazily created
> 	pass specific ranger instead of get_global_range_query.
> 	(pass_forwprop::execute): Disable that ranger at the end of pass if it has
> 	been created.
> 
> 	* c-c++-common/rotate-10.c: New test.
> 	* c-c++-common/rotate-11.c: New test.
> 
> --- gcc/tree-ssa-forwprop.cc.jj	2023-01-17 12:14:15.845088330 +0100
> +++ gcc/tree-ssa-forwprop.cc	2023-01-18 13:30:59.337914945 +0100
> @@ -52,6 +52,7 @@ along with GCC; see the file COPYING3.
>  #include "internal-fn.h"
>  #include "cgraph.h"
>  #include "tree-ssa.h"
> +#include "gimple-range.h"
>  
>  /* This pass propagates the RHS of assignment statements into use
>     sites of the LHS of the assignment.  It's basically a specialized
> @@ -1837,8 +1838,12 @@ defcodefor_name (tree name, enum tree_co
>     ((T) ((T2) X << Y)) | ((T) ((T2) X >> ((-Y) & (B - 1))))
>     ((T) ((T2) X << (int) Y)) | ((T) ((T2) X >> (int) ((-Y) & (B - 1))))
>  
> -   transform these into (last 2 only if ranger can prove Y < B):
> +   transform these into (last 2 only if ranger can prove Y < B
> +   or Y = N * B):
>     X r<< Y
> +   or
> +   X r<< (& & (B - 1))
> +   The latter for the forms with T2 wider than T if ranger can't prove Y < B.
>  
>     Or for:
>     (X << (Y & (B - 1))) | (X >> ((-Y) & (B - 1)))
> @@ -1868,6 +1873,7 @@ simplify_rotate (gimple_stmt_iterator *g
>    gimple *g;
>    gimple *def_arg_stmt[2] = { NULL, NULL };
>    int wider_prec = 0;
> +  bool add_masking = false;
>  
>    arg[0] = gimple_assign_rhs1 (stmt);
>    arg[1] = gimple_assign_rhs2 (stmt);
> @@ -1995,7 +2001,7 @@ simplify_rotate (gimple_stmt_iterator *g
>        tree cdef_arg1[2], cdef_arg2[2], def_arg2_alt[2];
>        enum tree_code cdef_code[2];
>        gimple *def_arg_alt_stmt[2] = { NULL, NULL };
> -      bool check_range = false;
> +      int check_range = 0;
>        gimple *check_range_stmt = NULL;
>        /* Look through conversion of the shift count argument.
>  	 The C/C++ FE cast any shift count argument to integer_type_node.
> @@ -2036,6 +2042,11 @@ simplify_rotate (gimple_stmt_iterator *g
>  		|| cdef_arg2[i] == def_arg2_alt[1 - i])
>  	      {
>  		rotcnt = cdef_arg2[i];
> +		check_range = -1;
> +		if (cdef_arg2[i] == def_arg2[1 - i])
> +		  check_range_stmt = def_arg_stmt[1 - i];
> +		else
> +		  check_range_stmt = def_arg_alt_stmt[1 - i];
>  		break;
>  	      }
>  	    defcodefor_name (cdef_arg2[i], &code, &tem, NULL);
> @@ -2048,6 +2059,11 @@ simplify_rotate (gimple_stmt_iterator *g
>  		    || tem == def_arg2_alt[1 - i]))
>  	      {
>  		rotcnt = tem;
> +		check_range = -1;
> +		if (tem == def_arg2[1 - i])
> +		  check_range_stmt = def_arg_stmt[1 - i];
> +		else
> +		  check_range_stmt = def_arg_alt_stmt[1 - i];
>  		break;
>  	      }
>  	  }
> @@ -2080,7 +2096,7 @@ simplify_rotate (gimple_stmt_iterator *g
>  		if (tem == def_arg2[1 - i] || tem == def_arg2_alt[1 - i])
>  		  {
>  		    rotcnt = tem;
> -		    check_range = true;
> +		    check_range = 1;
>  		    if (tem == def_arg2[1 - i])
>  		      check_range_stmt = def_arg_stmt[1 - i];
>  		    else
> @@ -2099,7 +2115,7 @@ simplify_rotate (gimple_stmt_iterator *g
>  			|| tem2 == def_arg2_alt[1 - i])
>  		      {
>  			rotcnt = tem2;
> -			check_range = true;
> +			check_range = 1;
>  			if (tem2 == def_arg2[1 - i])
>  			  check_range_stmt = def_arg_stmt[1 - i];
>  			else
> @@ -2144,17 +2160,44 @@ simplify_rotate (gimple_stmt_iterator *g
>  	  if (TREE_CODE (rotcnt) != SSA_NAME)
>  	    return false;
>  	  int_range_max r;
> -	  if (!get_global_range_query ()->range_of_expr (r, rotcnt,
> -							 check_range_stmt))
> -	    return false;
> +	  range_query *q = get_range_query (cfun);
> +	  if (q == get_global_range_query ())
> +	    q = enable_ranger (cfun);
> +	  if (!q->range_of_expr (r, rotcnt, check_range_stmt))
> +	    {
> +	      if (check_range > 0)
> +		return false;
> +	      r.set_varying (TREE_TYPE (rotcnt));
> +	    }
>  	  int prec = TYPE_PRECISION (TREE_TYPE (rotcnt));
>  	  signop sign = TYPE_SIGN (TREE_TYPE (rotcnt));
>  	  wide_int min = wide_int::from (TYPE_PRECISION (rtype), prec, sign);
>  	  wide_int max = wide_int::from (wider_prec - 1, prec, sign);
> -	  int_range<2> r2 (TREE_TYPE (rotcnt), min, max);
> +	  if (check_range < 0)
> +	    max = min;
> +	  int_range<1> r2 (TREE_TYPE (rotcnt), min, max);
>  	  r.intersect (r2);
>  	  if (!r.undefined_p ())
> -	    return false;
> +	    {
> +	      if (check_range > 0)
> +		{
> +		  int_range_max r3;
> +		  for (int i = TYPE_PRECISION (rtype) + 1; i < wider_prec;
> +		       i += TYPE_PRECISION (rtype))
> +		    {
> +		      int j = i + TYPE_PRECISION (rtype) - 2;
> +		      min = wide_int::from (i, prec, sign);
> +		      max = wide_int::from (MIN (j, wider_prec - 1),
> +					    prec, sign);
> +		      int_range<1> r4 (TREE_TYPE (rotcnt), min, max);
> +		      r3.union_ (r4);
> +		    }
> +		  r.intersect (r3);
> +		  if (!r.undefined_p ())
> +		    return false;
> +		}
> +	      add_masking = true;
> +	    }
>  	}
>        if (rotcnt == NULL_TREE)
>  	return false;
> @@ -2169,6 +2212,15 @@ simplify_rotate (gimple_stmt_iterator *g
>        gsi_insert_before (gsi, g, GSI_SAME_STMT);
>        rotcnt = gimple_assign_lhs (g);
>      }
> +  if (add_masking)
> +    {
> +      g = gimple_build_assign (make_ssa_name (TREE_TYPE (rotcnt)),
> +			       BIT_AND_EXPR, rotcnt,
> +			       build_int_cst (TREE_TYPE (rotcnt),
> +					      TYPE_PRECISION (rtype) - 1));
> +      gsi_insert_before (gsi, g, GSI_SAME_STMT);
> +      rotcnt = gimple_assign_lhs (g);
> +    }
>    lhs = gimple_assign_lhs (stmt);
>    if (!useless_type_conversion_p (rtype, TREE_TYPE (def_arg1[0])))
>      lhs = make_ssa_name (TREE_TYPE (def_arg1[0]));
> @@ -3958,6 +4010,9 @@ pass_forwprop::execute (function *fun)
>    BITMAP_FREE (to_purge);
>    BITMAP_FREE (need_ab_cleanup);
>  
> +  if (get_range_query (cfun) != get_global_range_query ())
> +    disable_ranger (cfun);
> +
>    if (cfg_changed)
>      todoflags |= TODO_cleanup_cfg;
>  
> --- gcc/testsuite/c-c++-common/rotate-10.c.jj	2023-01-18 13:12:05.917425710 +0100
> +++ gcc/testsuite/c-c++-common/rotate-10.c	2023-01-18 13:11:37.869835522 +0100
> @@ -0,0 +1,53 @@
> +/* PR tree-optimization/108440 */
> +/* { dg-do compile { target { { ilp32 || lp64 } || llp64 } } } */
> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> +/* { dg-final { scan-tree-dump-times " r<< " 5 "optimized" } } */
> +/* { dg-final { scan-tree-dump-times " \\\& 7;" 4 "optimized" } } */
> +
> +unsigned char
> +foo (unsigned char x, unsigned int y)
> +{
> +  if (y > __CHAR_BIT__)
> +    __builtin_unreachable ();
> +  return (x << y) | (x >> ((-y) & (__CHAR_BIT__ - 1)));
> +}
> +
> +unsigned char
> +bar (unsigned char x, unsigned int y)
> +{
> +  if (y >= __CHAR_BIT__)
> +    __builtin_unreachable ();
> +  return (x << y) | (x >> ((-y) & (__CHAR_BIT__ - 1)));
> +}
> +
> +unsigned char
> +baz (unsigned char x, unsigned int y)
> +{
> +  if (y > __CHAR_BIT__ && y != 2 * __CHAR_BIT__)
> +    __builtin_unreachable ();
> +  return (x << y) | (x >> ((-y) & (__CHAR_BIT__ - 1)));
> +}
> +
> +unsigned char
> +qux (unsigned char x, unsigned int y)
> +{
> +  if (y > __CHAR_BIT__ && y != 2 * __CHAR_BIT__ && y != __CHAR_BIT__ + 2)
> +    __builtin_unreachable ();
> +  return (x << y) | (x >> ((-y) & (__CHAR_BIT__ - 1)));
> +}
> +
> +unsigned char
> +quux (unsigned char x, unsigned int y)
> +{
> +  if (y > __CHAR_BIT__)
> +    __builtin_unreachable ();
> +  return (x << y) | (x >> (__CHAR_BIT__ - y));
> +}
> +
> +unsigned char
> +corge (unsigned char x, unsigned int y)
> +{
> +  if (y >= __CHAR_BIT__)
> +    __builtin_unreachable ();
> +  return (x << y) | (x >> (__CHAR_BIT__ - y));
> +}
> --- gcc/testsuite/c-c++-common/rotate-11.c.jj	2023-01-18 13:14:07.146654356 +0100
> +++ gcc/testsuite/c-c++-common/rotate-11.c	2023-01-18 13:14:19.916467769 +0100
> @@ -0,0 +1,53 @@
> +/* PR tree-optimization/108440 */
> +/* { dg-do compile { target { { ilp32 || lp64 } || llp64 } } } */
> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> +/* { dg-final { scan-tree-dump-times " r<< " 5 "optimized" } } */
> +/* { dg-final { scan-tree-dump-times " \\\& 7;" 4 "optimized" } } */
> +
> +unsigned char
> +foo (unsigned char x, unsigned int y)
> +{
> +  if (y > __CHAR_BIT__)
> +    return 42;
> +  return (x << y) | (x >> ((-y) & (__CHAR_BIT__ - 1)));
> +}
> +
> +unsigned char
> +bar (unsigned char x, unsigned int y)
> +{
> +  if (y >= __CHAR_BIT__)
> +    return 42;
> +  return (x << y) | (x >> ((-y) & (__CHAR_BIT__ - 1)));
> +}
> +
> +unsigned char
> +baz (unsigned char x, unsigned int y)
> +{
> +  if (y > __CHAR_BIT__ && y != 2 * __CHAR_BIT__)
> +    return 42;
> +  return (x << y) | (x >> ((-y) & (__CHAR_BIT__ - 1)));
> +}
> +
> +unsigned char
> +qux (unsigned char x, unsigned int y)
> +{
> +  if (y > __CHAR_BIT__ && y != 2 * __CHAR_BIT__ && y != __CHAR_BIT__ + 2)
> +    return 42;
> +  return (x << y) | (x >> ((-y) & (__CHAR_BIT__ - 1)));
> +}
> +
> +unsigned char
> +quux (unsigned char x, unsigned int y)
> +{
> +  if (y > __CHAR_BIT__)
> +    return 42;
> +  return (x << y) | (x >> (__CHAR_BIT__ - y));
> +}
> +
> +unsigned char
> +corge (unsigned char x, unsigned int y)
> +{
> +  if (y >= __CHAR_BIT__)
> +    return 42;
> +  return (x << y) | (x >> (__CHAR_BIT__ - y));
> +}
> 
> 	Jakub
> 
>
  

On 1/19/23 09:41, Jakub Jelinek wrote:

> +	  range_query *q = get_range_query (cfun);
> +	  if (q == get_global_range_query ())
> +	    q = enable_ranger (cfun);

Oh, neat.  Clever.  I hadn't thought about that.

> +	  if (!q->range_of_expr (r, rotcnt, check_range_stmt))
> +	    {
> +	      if (check_range > 0)
> +		return false;
> +	      r.set_varying (TREE_TYPE (rotcnt));
> +	    }
>   	  int prec = TYPE_PRECISION (TREE_TYPE (rotcnt));
>   	  signop sign = TYPE_SIGN (TREE_TYPE (rotcnt));
>   	  wide_int min = wide_int::from (TYPE_PRECISION (rtype), prec, sign);
>   	  wide_int max = wide_int::from (wider_prec - 1, prec, sign);
> -	  int_range<2> r2 (TREE_TYPE (rotcnt), min, max);
> +	  if (check_range < 0)
> +	    max = min;
> +	  int_range<1> r2 (TREE_TYPE (rotcnt), min, max);
 >   	  r.intersect (r2);

Currently int_range<1> is a legacy range (anti ranges and such 
internally).  It's better to use <2> as the use of r2 will have to be 
converted to a multi-range before intersecting.  FYI, <2> is the 
smallest multi-range.

This is really an implementation detail, so don't bother changing it, 
even though it's slightly slower.  In the next release we'll nuke 
legacy, and <1> will mean what you think it means...the smallest range 
with one sub-range (and none of that anti range business internally).

Thanks.
Aldy