[Polly] Check validity of new access relations. NFC.

[Meinersbur]

Summary

There are some constraints on maps that can be access relations. In builds with assertions enabled, verify

• The access domain is the same space as the statement's domain (modulo parameters)
• Whether an access is defined for every instance of the statement (codegen does not yet support partial access relations)
• Whether the access range links to an array, represented by a ScopArrayInfo
• The number of access dimensions equals the dimensions of the array.

[Meinersbur]

The test Isl/CodeGen/MemAccess/create_arrays.ll fails this with the assertions:

Assertion failed: isl_space_dim(NewAccessSpace, isl_dim_set) == Dims && "Access dims must match array dims"

It creates an array with 3 dimensions ("E") but adds an access with only 2 indices ("E[i2, i0]").

[grosser]

Hi Michael.

these changes look good to me, but we should probably coordinate with Roman before committing them. Thanks for already reaching out to him.

@Roman: As you have been working in this area, could you please also review this change?

Best,
Tobias

include/polly/Support/ScopHelper.h

451 ↗

(On Diff #69339)

This really belongs into isl. We can probably add this here for now, as having a local copy has minimal cost, but we should probably contribute a corresponding patch upstream.

[gareevroman]

Hi Michael,

thank you for the patch. It looks good also to me.

include/polly/Support/ScopHelper.h

451 ↗

(On Diff #69339)

We should possibly rename it to, for example, SpaceIsCompatible, if we want to declare it here.

[gareevroman]

include/polly/Support/ScopHelper.h

451 ↗

(On Diff #69339)

"spaceIsCompatible"

[Meinersbur]

Use ISL's new isl_space_has_equal_tuples

[Meinersbur]

rebase; also check for indirect array accesses

lib/Analysis/ScopInfo.cpp

bool MemoryAccess::isStrideZero(__isl_take const isl_map *Schedule) const {
   return isStrideX(Schedule, 0);
 }
 
 bool MemoryAccess::isStrideOne(__isl_take const isl_map *Schedule) const {
   return isStrideX(Schedule, 1);
 }
 
 void MemoryAccess::setNewAccessRelation(__isl_take isl_map *NewAccess) {
+  assert(NewAccess);
+
+#ifndef NDEBUG
+  // Check domain space compatibility.
+  auto *NewSpace = isl_map_get_space(NewAccess);
+  auto *NewDomainSpace = isl_space_domain(isl_space_copy(NewSpace));
+  auto *OriginalDomainSpace = getStatement()->getDomainSpace();
+  assert(isl_space_has_equal_tuples(OriginalDomainSpace, NewDomainSpace));
+  isl_space_free(NewDomainSpace);
+  isl_space_free(OriginalDomainSpace);
+
+  // Check whether there is an access for every statement instance.
+  auto *StmtDomain = getStatement()->getDomain();
+  StmtDomain = isl_set_intersect_params(
+      StmtDomain, getStatement()->getParent()->getContext());
+  auto *NewDomain = isl_map_domain(isl_map_copy(NewAccess));
+  assert(isl_set_is_subset(StmtDomain, NewDomain) &&
+         "Partial accesses not supported");
+  isl_set_free(NewDomain);
+  isl_set_free(StmtDomain);
+
+  // Check whether access dimensions correspond to number of dimensions of the
+  // accesses array.
+  auto *NewAccessSpace = isl_space_range(NewSpace);
+  assert(isl_space_has_tuple_id(NewAccessSpace, isl_dim_set) &&
+         "Must specify the array that is accessed");
+  auto *NewArrayId = isl_space_get_tuple_id(NewAccessSpace, isl_dim_set);
+  auto *SAI = static_cast<ScopArrayInfo *>(isl_id_get_user(NewArrayId));
+  assert(SAI && "Must set a ScopArrayInfo");
+  assert(!SAI->getBasePtrOriginSAI() &&
+         "Indirect array not supported by codegen");
+  auto Dims = SAI->getNumberOfDimensions();
+  assert(isl_space_dim(NewAccessSpace, isl_dim_set) == Dims &&
+         "Access dims must match array dims");
+  isl_space_free(NewAccessSpace);
+  isl_id_free(NewArrayId);
+#endif
+
   isl_map_free(NewAccessRelation);
   NewAccessRelation = NewAccess;
 }
 
 //===----------------------------------------------------------------------===//
 
 __isl_give isl_map *ScopStmt::getSchedule() const {
   isl_set *Domain = getDomain();