[Polly] Fix codegen assertions to account for DefinedBehaviorContext (#209188)

DeLICM may produce new read access relations whose domain is restricted
to the DefinedBehaviorContext (e.g., only valid when a parameter ensures
no UB). The validation in setNewAccessRelation already accounts for
this, but the debug assertions in createNewAccesses and
generateScalarLoads did not, causing false assertion failures during
code generation.

Intersect the checked domains with getBestKnownDefinedBehaviorContext()
to match the contract that DeLICM relies on.

Fixes #205732

(cherry picked from commit ea61254564)

polly/lib/CodeGen/BlockGenerators.cpp

@@ -555,6 +555,11 @@ void BlockGenerator::generateScalarLoads(
 #ifndef NDEBUG
     auto StmtDom =
         Stmt.getDomain().intersect_params(Stmt.getParent()->getContext());
+    // Restrict to defined behavior context to match DeLICM's contract:
+    // new read accesses are only required to cover the defined-behavior
+    // subset of the domain.
+    StmtDom = StmtDom.intersect_params(
+        Stmt.getParent()->getBestKnownDefinedBehaviorContext());
     auto AccDom = MA->getAccessRelation().domain();
     assert(!StmtDom.is_subset(AccDom).is_false() &&
            "Scalar must be loaded in all statement instances");

polly/lib/CodeGen/IslNodeBuilder.cpp

@@ -846,9 +846,17 @@ IslNodeBuilder::createNewAccesses(ScopStmt *Stmt,
                                      Stmt->getParent()->getContext().release());
       SchedDom = isl_set_intersect_params(
           SchedDom, Stmt->getParent()->getContext().release());
-      assert(isl_set_is_subset(SchedDom, AccDom) &&
+      // Restrict to defined behavior context to match DeLICM's contract:
+      // new read accesses are only required to cover the defined-behavior
+      // subset of the domain.
+      auto *DefinedBehavior =
+          Stmt->getParent()->getBestKnownDefinedBehaviorContext().release();
+      SchedDom =
+          isl_set_intersect_params(SchedDom, isl_set_copy(DefinedBehavior));
+      Dom = isl_set_intersect_params(Dom, DefinedBehavior);
+      assert(isl_set_is_subset(SchedDom, AccDom) != isl_bool_false &&
              "Access relation not defined on full schedule domain");
-      assert(isl_set_is_subset(Dom, AccDom) &&
+      assert(isl_set_is_subset(Dom, AccDom) != isl_bool_false &&
              "Access relation not defined on full domain");
       isl_set_free(AccDom);
       isl_set_free(SchedDom);

polly/test/CodeGen/issue205732.ll

@@ -0,0 +1,40 @@
+; RUN: opt %loadNPMPolly -passes=polly -S %s | FileCheck %s
+;
+; https://github.com/llvm/llvm-project/issues/205732
+; When DeLICM maps a scalar to an array element, the new access relation
+; may only be valid within the DefinedBehaviorContext (i.e., for parameter
+; values where the original program has no undefined behavior). Code
+; generation must not assert failure for such partial-domain read accesses.
+;
+; CHECK: polly.start:
+
+define void @foo(i32 %w, ptr %dst, i64 %n) {
+entry:
+  br label %for.outer
+
+for.outer:
+  %i = phi i64 [ %i.next, %for.mid.exit ], [ 0, %entry ]
+  br label %for.mid
+
+for.mid:
+  br label %for.inner
+
+for.inner:
+  %0 = phi i32 [ 0, %for.mid ], [ 1, %for.inner ]
+  %1 = load i16, ptr null, align 2
+  %cond1 = icmp eq i32 0, %w
+  br i1 %cond1, label %for.inner.exit, label %for.inner
+
+for.inner.exit:
+  br i1 true, label %for.mid.exit, label %for.mid
+
+for.mid.exit:
+  %ptr = getelementptr [4 x i8], ptr %dst, i64 %i
+  store i32 %0, ptr %ptr, align 4
+  %i.next = add i64 %i, 1
+  %cond2 = icmp eq i64 %i, %n
+  br i1 %cond2, label %for.outer.exit, label %for.outer
+
+for.outer.exit:
+  ret void
+}