Re: [PATCH] c++: Incremental fix for g++.dg/gomp/for-21.C [PR84469]

[Jason Merrill <jason@redhat.com>]

On 11/29/22 07:32, Jakub Jelinek wrote:
> Hi!
> 
> The PR84469 patch I've just posted regresses the for-21.C testcase,
> when in OpenMP loop there are at least 2 associated loops and
> in a template outer structured binding with non type dependent expression
> is used in the expressions of some inner loop, we don't diagnose those
> any longer, as the (weirdly worded) diagnostics was only done during
> finish_id_expression -> mark_used which for the inner loop expressions
> happens before the structured bindings are finalized.  When in templates,
> mark_used doesn't diagnose uses of non-deduced variables, and if the
> range for expression is type dependent, it is similarly diagnosed during
> instantiation.  But newly with the PR84469 fix if the range for expression
> is not type dependent, there is no place that would diagnose it, as during
> instantiation the structured bindings are already deduced.
> 
> The following patch diagnoses it in that case during finish_omp_for (for
> consistency with the same weird message).
> 
> I'll commit this to trunk if the other patch is approved and it passes
> bootstrap/regtest.
> 
> 2022-11-29  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR c++/84469
> 	* semantics.cc: Define INCLUDE_MEMORY before including system.h.
> 	(struct finish_omp_for_data): New type.
> 	(finish_omp_for_decomps_r): New function.
> 	(finish_omp_for): Diagnose uses of non-type-dependent range for
> 	loop decompositions in inner OpenMP associated loops in templates.
> 
> 	* g++.dg/gomp/for-21.C (f6): Adjust lines of expected diagnostics.
> 	* g++.dg/gomp/for-22.C: New test.
> 
> --- gcc/cp/semantics.cc.jj	2022-11-19 09:21:14.897436616 +0100
> +++ gcc/cp/semantics.cc	2022-11-29 12:58:36.165771985 +0100
> @@ -24,6 +24,7 @@ along with GCC; see the file COPYING3.
>   <http://www.gnu.org/licenses/>.  */
>   
>   #include "config.h"
> +#define INCLUDE_MEMORY
>   #include "system.h"
>   #include "coretypes.h"
>   #include "target.h"
> @@ -10401,6 +10402,47 @@ handle_omp_for_class_iterator (int i, lo
>     return false;
>   }
>   
> +struct finish_omp_for_data {
> +  std::unique_ptr<hash_set<tree>> decomps;
> +  bool fail;
> +  location_t loc;
> +};
> +
> +/* Helper function for finish_omp_for.  Diagnose uses of structured
> +   bindings of OpenMP collapsed loop range for loops in the associated
> +   loops.  If not processing_template_decl, this is diagnosed by
> +   finish_id_expression -> mark_used before the range for is deduced.
> +   And if processing_template_decl and the range for expression is
> +   type dependent, it is similarly diagnosed during instantiation.
> +   Only when processing_template_decl and range for expression is
> +   not type dependent, we wouldn't diagnose it at all, so do it
> +   from finish_omp_for in that case.  */
> +
> +static tree
> +finish_omp_for_decomps_r (tree *tp, int *, void *d)
> +{
> +  if (VAR_P (*tp)
> +      && DECL_DECOMPOSITION_P (*tp)
> +      && !type_dependent_expression_p (*tp)
> +      && DECL_HAS_VALUE_EXPR_P (*tp))
> +    {
> +      tree v = DECL_VALUE_EXPR (*tp);
> +      if (TREE_CODE (v) == ARRAY_REF
> +	  && VAR_P (TREE_OPERAND (v, 0))
> +	  && DECL_DECOMPOSITION_P (TREE_OPERAND (v, 0)))
> +	{
> +	  finish_omp_for_data *data = (finish_omp_for_data *) d;
> +	  if (data->decomps->contains (TREE_OPERAND (v, 0)))
> +	    {
> +	      error_at (data->loc, "use of %qD before deduction of %<auto%>",
> +			*tp);
> +	      data->fail = true;
> +	    }
> +	}
> +    }
> +  return NULL_TREE;
> +}
> +
>   /* Build and validate an OMP_FOR statement.  CLAUSES, BODY, COND, INCR
>      are directly for their associated operands in the statement.  DECL
>      and INIT are a combo; if DECL is NULL then INIT ought to be a
> @@ -10419,6 +10461,7 @@ finish_omp_for (location_t locus, enum t
>     int i;
>     int collapse = 1;
>     int ordered = 0;
> +  finish_omp_for_data data;
>   
>     gcc_assert (TREE_VEC_LENGTH (declv) == TREE_VEC_LENGTH (initv));
>     gcc_assert (TREE_VEC_LENGTH (declv) == TREE_VEC_LENGTH (condv));
> @@ -10479,7 +10522,25 @@ finish_omp_for (location_t locus, enum t
>   	elocus = EXPR_LOCATION (init);
>   
>         if (cond == global_namespace)
> -	continue;
> +	{
> +	  gcc_assert (processing_template_decl);
> +	  if (TREE_VEC_LENGTH (declv) > 1
> +	      && VAR_P (decl)
> +	      && DECL_DECOMPOSITION_P (decl)
> +	      && !type_dependent_expression_p (decl))
> +	    {
> +	      gcc_assert (DECL_HAS_VALUE_EXPR_P (decl));
> +	      tree v = DECL_VALUE_EXPR (decl);
> +	      gcc_assert (TREE_CODE (v) == ARRAY_REF
> +			  && VAR_P (TREE_OPERAND (v, 0))
> +			  && DECL_DECOMPOSITION_P (TREE_OPERAND (v, 0)));
> +	      if (!data.decomps)
> +		data.decomps
> +		  = std::unique_ptr<hash_set<tree>> (new hash_set<tree>);
> +	      data.decomps->add (TREE_OPERAND (v, 0));
> +	    }
> +	  continue;
> +	}
>   
>         if (cond == NULL)
>   	{
> @@ -10497,6 +10558,37 @@ finish_omp_for (location_t locus, enum t
>         TREE_VEC_ELT (initv, i) = init;
>       }
>   
> +  if (data.decomps)
> +    {
> +      data.fail = false;
> +      data.loc = locus;
> +      hash_set<tree> pset;
> +      for (i = 0; i < TREE_VEC_LENGTH (declv); i++)
> +	{
> +	  init = TREE_VEC_ELT (initv, i);
> +	  cond = TREE_VEC_ELT (condv, i);
> +	  incr = TREE_VEC_ELT (incrv, i);
> +	  data.loc = EXPR_LOC_OR_LOC (init, locus);
> +	  cp_walk_tree (&init, finish_omp_for_decomps_r, &data, &pset);
> +	  data.loc = EXPR_LOC_OR_LOC (cond, locus);
> +	  cp_walk_tree (&cond, finish_omp_for_decomps_r, &data, &pset);
> +	  data.loc = EXPR_LOC_OR_LOC (incr, locus);
> +	  cp_walk_tree (&incr, finish_omp_for_decomps_r, &data, &pset);
> +	}
> +      if (orig_inits && !data.fail)
> +	{
> +	  tree orig_init;
> +	  FOR_EACH_VEC_ELT (*orig_inits, i, orig_init)
> +	    {
> +	      data.loc = EXPR_LOC_OR_LOC (orig_init, locus);
> +	      cp_walk_tree (&orig_init, finish_omp_for_decomps_r,
> +			    &data, &pset);
> +	    }
> +	}
> +      if (data.fail)
> +	return NULL;
> +    }
> +
>     if (orig_inits)
>       {
>         bool fail = false;
> --- gcc/testsuite/g++.dg/gomp/for-21.C.jj	2020-01-12 11:54:37.178401867 +0100
> +++ gcc/testsuite/g++.dg/gomp/for-21.C	2022-11-29 13:06:59.038410557 +0100
> @@ -54,9 +54,9 @@ void
>   f6 (S (&a)[10])
>   {
>     #pragma omp for collapse (2)
> -  for (auto [i, j, k] : a)			// { dg-error "use of 'i' before deduction of 'auto'" "" { target *-*-* } .-1 }
> +  for (auto [i, j, k] : a)			// { dg-error "use of 'i' before deduction of 'auto'" }
>       for (int l = i; l < j; l += k)		// { dg-error "use of 'j' before deduction of 'auto'" }
> -      ;						// { dg-error "use of 'k' before deduction of 'auto'" "" { target *-*-* } .-3 }
> +      ;						// { dg-error "use of 'k' before deduction of 'auto'" "" { target *-*-* } .-1 }

Hmm, this error is surprising: since the initializer is non-dependent, 
we should have deduced immediately.  I'd expect the same error as in the 
non-structured-binding cases, "* expression refers to iteration variable".

>   }
>   
>   template <typename T>
> --- gcc/testsuite/g++.dg/gomp/for-22.C.jj	2022-11-29 13:07:10.859237506 +0100
> +++ gcc/testsuite/g++.dg/gomp/for-22.C	2022-11-29 13:09:50.743897003 +0100
> @@ -0,0 +1,57 @@
> +// { dg-do compile { target c++17 } }
> +
> +namespace std {
> +  template<typename T> struct tuple_size;
> +  template<int, typename> struct tuple_element;
> +}
> +
> +struct A {
> +  int i;
> +  template <int I> int& get() { return i; }
> +};
> +
> +template<> struct std::tuple_size<A> { static const int value = 3; };
> +template<int I> struct std::tuple_element<I,A> { using type = int; };
> +
> +struct B {
> +  A *begin();
> +  A *end();
> +};
> +
> +void
> +f1 (B a)
> +{
> +  #pragma omp for collapse (2)
> +  for (auto [i, j, k] : a)			// { dg-error "use of 'i' before deduction of 'auto'" "" { target *-*-* } .+1 }
> +    for (int l = i; l < j; l += k)		// { dg-error "use of 'j' before deduction of 'auto'" }
> +      ;						// { dg-error "use of 'k' before deduction of 'auto'" "" { target *-*-* } .-1 }
> +}
> +
> +template <int N>
> +void
> +f2 (B a)
> +{
> +  #pragma omp for collapse (2)
> +  for (auto [i, j, k] : a)			// { dg-error "use of 'i' before deduction of 'auto'" "" { target *-*-* } .+1 }
> +    for (int l = i; l < j; l += k)		// { dg-error "use of 'j' before deduction of 'auto'" }
> +      ;						// { dg-error "use of 'k' before deduction of 'auto'" "" { target *-*-* } .-1 }
> +}
> +
> +template <typename T>
> +void
> +f3 (T a)
> +{
> +  #pragma omp for collapse (2)
> +  for (auto [i, j, k] : a)			// { dg-error "use of 'i' before deduction of 'auto'" "" { target *-*-* } .-1 }
> +    for (int l = i; l < j; l += k)		// { dg-error "use of 'j' before deduction of 'auto'" }
> +      ;						// { dg-error "use of 'k' before deduction of 'auto'" "" { target *-*-* } .-3 }
> +}
> +
> +void
> +test ()
> +{
> +  B b;
> +  f1 (b);
> +  f2 <0> (b);
> +  f3 <B> (b);
> +}
> 
> 	Jakub
>