Index: lib/CodeGen/PPCGCodeGeneration.cpp
===================================================================
--- lib/CodeGen/PPCGCodeGeneration.cpp
+++ lib/CodeGen/PPCGCodeGeneration.cpp
@@ -2632,6 +2632,77 @@
     return Names;
   }
 
+  /// Remove unreferenced parameter dimensions from union_map.
+  isl::union_map removeUnusedParameters(isl::union_map UMap) {
+    auto New = isl::union_map::empty(isl::space(UMap.get_ctx(), 0, 0));
+
+    auto Lambda = [&New](isl::map S) -> isl::stat {
+      int Removed = 0;
+      int NumDims = S.dim(isl::dim::param);
+      for (long i = 0; i < NumDims; i++) {
+        int Dim = i - Removed;
+        if (!S.involves_dims(isl::dim::param, Dim, 1)) {
+          S = S.remove_dims(isl::dim::param, Dim, 1);
+          Removed++;
+        }
+      }
+      New = New.unite(S);
+      return isl::stat::ok;
+    };
+
+    UMap.foreach_map(Lambda);
+    return New;
+  }
+
+  /// Remove unreferenced parameter dimensions from union_set.
+  isl::union_set removeUnusedParameters(isl::union_set USet) {
+    auto New = isl::union_set::empty(isl::space(USet.get_ctx(), 0, 0));
+
+    auto Lambda = [&New](isl::set S) -> isl::stat {
+      int Removed = 0;
+      int NumDims = S.dim(isl::dim::param);
+      for (long i = 0; i < NumDims; i++) {
+        int Dim = i - Removed;
+        if (!S.involves_dims(isl::dim::param, Dim, 1)) {
+          S = S.remove_dims(isl::dim::param, Dim, 1);
+          Removed++;
+        }
+      }
+      New = New.unite(S);
+      return isl::stat::ok;
+    };
+
+    USet.foreach_set(Lambda);
+    return New;
+  }
+
+  /// Simplify PPCG scop to improve compile time.
+  ///
+  /// We drop unused parameter dimensions to reduce the size of the sets we are
+  /// working with. Especially the computed dependences tend to accumulate a lot
+  /// of parameters that are present in the input memory accesses, but often are
+  /// not necessary to express the actual dependences. As isl represents maps
+  /// and sets with dense matrices, reducing the dimensionality of isl sets
+  /// commonly reduces code generation performance.
+  void simplifyPPCGScop(ppcg_scop *PPCGScop) {
+    PPCGScop->domain =
+        removeUnusedParameters(isl::manage(PPCGScop->domain)).release();
+
+    PPCGScop->dep_forced =
+        removeUnusedParameters(isl::manage(PPCGScop->dep_forced)).release();
+    PPCGScop->dep_false =
+        removeUnusedParameters(isl::manage(PPCGScop->dep_false)).release();
+    PPCGScop->dep_flow =
+        removeUnusedParameters(isl::manage(PPCGScop->dep_flow)).release();
+    PPCGScop->tagged_dep_flow =
+        removeUnusedParameters(isl::manage(PPCGScop->tagged_dep_flow))
+            .release();
+
+    PPCGScop->tagged_dep_order =
+        removeUnusedParameters(isl::manage(PPCGScop->tagged_dep_order))
+            .release();
+  }
+
   /// Create a new PPCG scop from the current scop.
   ///
   /// The PPCG scop is initialized with data from the current polly::Scop. From
@@ -2689,6 +2760,7 @@
     compute_tagger(PPCGScop);
     compute_dependences(PPCGScop);
     eliminate_dead_code(PPCGScop);
+    simplifyPPCGScop(PPCGScop);
 
     return PPCGScop;
   }
@@ -3132,8 +3204,12 @@
 
     int has_permutable = has_any_permutable_node(Schedule);
 
-    Schedule =
-        isl_schedule_align_params(Schedule, S->getFullParamSpace().release());
+    /// Copy to and from device functions may introduce new parameters, which
+    /// must be present in the schedule tree root for code generation. Hence,
+    /// we ensure that all possible parameters are introduced from this point.
+    if (!PollyManagedMemory)
+      Schedule =
+          isl_schedule_align_params(Schedule, S->getFullParamSpace().release());
 
     if (!has_permutable || has_permutable < 0) {
       Schedule = isl_schedule_free(Schedule);