[GPGPU] Make sure that all parameter dimensions are set in schedule

[grosser]

Summary

In case the option -polly-ignore-parameter-bounds is set, not all parameters
will be added to context and domains. This is useful to keep the size of the
sets and maps we work with small. Unfortunately, for AST generation it is
necessary to ensure all parameters are part of the schedule tree. Hence,
we modify the GPGPU code generation to make sure this is the case.

To obtain the necessary information we expose a new function
Scop::getFullParamSpace(). We also make a couple of functions const to be
able to make SCoP::getFullParamSpace() const.

[bollu]

@grosser - Can you comment on my concern about Fortran arrays? See ScopArrayInfo::setAndApplyFAD for this new parameter synthesis.

include/polly/ScopInfo.h

2519

• Nit: In case the full set of parameters is needed, see @getFullParamSpace (bold missing?)

2525

• Nit: all parameter s. (bold missing?)

lib/Analysis/ScopInfo.cpp

4311

I am not sure if only taking the SCEVs are enough. IIRC, if an array is a fortran array, it can have an extra "virtual parameter" in the outermost dimension that has no corresponding SCEV. That's a corner case.

4315

Nit: not sure if auto is valid here, because I had to lookup that Parameter would be a const SCEV *

[grosser]

Addressed Siddharth's comments

[grosser]

I addressed your comments.

[bollu]

LGTM. Please refactor the Fortran changes to an [NFC] patch before applying this patch, if it makes sense.

include/polly/ScopInfo.h

private:
   /// only one of them is chosen as a representing element that will be
   /// modeled as a parameter. The others have to be normalized, i.e.,
   /// replaced by the representing element of their equivalence class, in order
   /// to get the correct parameter value, e.g., in the SCEVAffinator.
   ///
   /// @param S The SCEV to normalize.
   ///
   /// @return The representing SCEV for invariant loads or @p S if none.
-  const SCEV *getRepresentingInvariantLoadSCEV(const SCEV *S);
+  const SCEV *getRepresentingInvariantLoadSCEV(const SCEV *S) const;
 
   /// Create a new SCoP statement for @p BB.
   ///
   /// A new statement for @p BB will be created and added to the statement
   /// vector
   /// and map.
   ///
   /// @param BB              The basic block we build the statement for.
inline const_array_range arrays() const {
     return const_array_range(array_begin(), array_end());
   }
 
   /// Return the isl_id that represents a certain parameter.
   ///
   /// @param Parameter A SCEV that was recognized as a Parameter.
   ///
   /// @return The corresponding isl_id or NULL otherwise.
-  __isl_give isl_id *getIdForParam(const SCEV *Parameter);
+  __isl_give isl_id *getIdForParam(const SCEV *Parameter) const;
 
   /// Get the maximum region of this static control part.
   ///
   /// @return The maximum region of this static control part.
   inline const Region &getRegion() const { return R; }
   inline Region &getRegion() { return R; }
 
   /// Return the function this SCoP is in.
public:
 
   /// Get the name of this Scop.
   std::string getNameStr() const;
 
   /// Get the constraint on parameter of this Scop.
   ///
   /// @return The constraint on parameter of this Scop.
   __isl_give isl_set *getContext() const;
+
+  /// Return space of isl context parameters.
+  ///
+  /// Returns the set of context parameters that are currently constrained. In
+  /// case the full set of parameters is needed
   __isl_give isl_space *getParamSpace() const;
 
+  /// Return the full space of parameters.
+  ///
+  /// getParamSpace will only return the parameters of the context that are
+  /// actually constrained, whereas getFullParamSpace will return all parameter.
+  /// This is useful in cases, where we need to ensure all parameters are
+  /// available, as certain isl functions will abort if this is not the case.
+  isl::space getFullParamSpace() const;
+
   /// Get the assumed context for this Scop.
   ///
   /// @return The assumed context of this Scop.
   __isl_give isl_set *getAssumedContext() const;
 
   /// Return true if the optimized SCoP can be executed.
   ///
   /// In addition to the runtime check context this will also utilize the domain

lib/Analysis/ScopInfo.cpp

void Scop::setContext(__isl_take isl_set *NewContext) {
   isl_set_free(Context);
   Context = NewContext;
 }
 
 namespace {
 /// Remap parameter values but keep AddRecs valid wrt. invariant loads.
 struct SCEVSensitiveParameterRewriter
     : public SCEVRewriteVisitor<SCEVSensitiveParameterRewriter> {
-  ValueToValueMap &VMap;
+  const ValueToValueMap &VMap;
 
 public:
-  SCEVSensitiveParameterRewriter(ValueToValueMap &VMap, ScalarEvolution &SE)
+  SCEVSensitiveParameterRewriter(const ValueToValueMap &VMap,
+                                 ScalarEvolution &SE)
       : SCEVRewriteVisitor(SE), VMap(VMap) {}
 
   static const SCEV *rewrite(const SCEV *E, ScalarEvolution &SE,
-                             ValueToValueMap &VMap) {
+                             const ValueToValueMap &VMap) {
     SCEVSensitiveParameterRewriter SSPR(VMap, SE);
     return SSPR.visit(E);
   }
 
   const SCEV *visitAddRecExpr(const SCEVAddRecExpr *E) {
     auto *Start = visit(E->getStart());
     auto *AddRec = SE.getAddRecExpr(SE.getConstant(E->getType(), 0),
                                     visit(E->getStepRecurrence(SE)),
                                     E->getLoop(), SCEV::FlagAnyWrap);
     return SE.getAddExpr(Start, AddRec);
   }
 
   const SCEV *visitUnknown(const SCEVUnknown *E) {
     if (auto *NewValue = VMap.lookup(E->getValue()))
       return SE.getUnknown(NewValue);
     return E;
   }
 };
 
 /// Check whether we should remap a SCEV expression.
 struct SCEVFindInsideScop : public SCEVTraversal<SCEVFindInsideScop> {
-  ValueToValueMap &VMap;
+  const ValueToValueMap &VMap;
   bool FoundInside = false;
-  Scop *S;
+  const Scop *S;
 
 public:
-  SCEVFindInsideScop(ValueToValueMap &VMap, ScalarEvolution &SE, Scop *S)
+  SCEVFindInsideScop(const ValueToValueMap &VMap, ScalarEvolution &SE,
+                     const Scop *S)
       : SCEVTraversal(*this), VMap(VMap), S(S) {}
 
   static bool hasVariant(const SCEV *E, ScalarEvolution &SE,
-                         ValueToValueMap &VMap, Scop *S) {
+                         const ValueToValueMap &VMap, const Scop *S) {
     SCEVFindInsideScop SFIS(VMap, SE, S);
     SFIS.visitAll(E);
     return SFIS.FoundInside;
   }
 
   bool follow(const SCEV *E) {
     if (auto *AddRec = dyn_cast<SCEVAddRecExpr>(E)) {
       FoundInside |= S->getRegion().contains(AddRec->getLoop());
     } else if (auto *Unknown = dyn_cast<SCEVUnknown>(E)) {
       if (Instruction *I = dyn_cast<Instruction>(Unknown->getValue()))
         FoundInside |= S->getRegion().contains(I) && !VMap.count(I);
     }
     return !FoundInside;
   }
   bool isDone() { return FoundInside; }
 };
 } // namespace
 
-const SCEV *Scop::getRepresentingInvariantLoadSCEV(const SCEV *E) {
+const SCEV *Scop::getRepresentingInvariantLoadSCEV(const SCEV *E) const {
   // Check whether it makes sense to rewrite the SCEV.  (ScalarEvolution
   // doesn't like addition between an AddRec and an expression that
   // doesn't have a dominance relationship with it.)
   if (SCEVFindInsideScop::hasVariant(E, *SE, InvEquivClassVMap, this))
     return E;
 
   // Rewrite SCEV.
   return SCEVSensitiveParameterRewriter::rewrite(E, *SE, InvEquivClassVMap);
for (const SCEV *Parameter : NewParameters) {
     Parameter = extractConstantFactor(Parameter, *SE).second;
     Parameter = getRepresentingInvariantLoadSCEV(Parameter);
 
     if (Parameters.insert(Parameter))
       createParameterId(Parameter);
   }
 }
 
-__isl_give isl_id *Scop::getIdForParam(const SCEV *Parameter) {
+__isl_give isl_id *Scop::getIdForParam(const SCEV *Parameter) const {
   // Normalize the SCEV to get the representing element for an invariant load.
   Parameter = getRepresentingInvariantLoadSCEV(Parameter);
   return isl_id_copy(ParameterIds.lookup(Parameter));
 }
 
 __isl_give isl_set *
 Scop::addNonEmptyDomainConstraints(__isl_take isl_set *C) const {
   isl_set *DomainContext = isl_union_set_params(getDomains());
static isl_set *addFortranArrayOutermostDimParams(__isl_give isl_set *Context,
   return Context;
 }
 
 void Scop::realignParams() {
   if (PollyIgnoreParamBounds)
     return;
 
   // Add all parameters into a common model.
-  isl_space *Space = isl_space_params_alloc(getIslCtx(), ParameterIds.size());
-
-  unsigned PDim = 0;
-  for (const auto *Parameter : Parameters) {
-    isl_id *id = getIdForParam(Parameter);
-    Space = isl_space_set_dim_id(Space, isl_dim_param, PDim++, id);
-  }
+  isl::space Space = getFullParamSpace();
 
   // Align the parameters of all data structures to the model.
-  Context = isl_set_align_params(Context, Space);
+  Context = isl_set_align_params(Context, Space.copy());
 
   // Add the outermost dimension of the Fortran arrays into the Context.
   // See the description of the function for more information.
   Context = addFortranArrayOutermostDimParams(Context, arrays());
 
   // As all parameters are known add bounds to them.
   addParameterBounds();
 
std::pair<std::string, std::string> Scop::getEntryExitStr() const {
   return std::make_pair(EntryName, ExitName);
 }
 
 __isl_give isl_set *Scop::getContext() const { return isl_set_copy(Context); }
 __isl_give isl_space *Scop::getParamSpace() const {
   return isl_set_get_space(Context);
 }
 
+isl::space Scop::getFullParamSpace() const {
+  isl::space Space = isl::space::params_alloc(getIslCtx(), ParameterIds.size());
+
+  unsigned PDim = 0;
+  for (const auto *Parameter : Parameters) {
+    isl::id Id = isl::manage(getIdForParam(Parameter));
+    Space = Space.set_dim_id(isl::dim::param, PDim++, Id);
+  }
+  return Space;
+}
+
 __isl_give isl_set *Scop::getAssumedContext() const {
   assert(AssumedContext && "Assumed context not yet built");
   return isl_set_copy(AssumedContext);
 }
 
 bool Scop::isProfitable(bool ScalarsAreUnprofitable) const {
   if (PollyProcessUnprofitable)
     return true;

lib/CodeGen/PPCGCodeGeneration.cpp

gpu_gen *generateGPU(ppcg_scop *PPCGScop, gpu_prog *PPCGProg) {
     isl_options_set_schedule_outer_coincidence(PPCGGen->ctx, true);
     isl_options_set_schedule_maximize_band_depth(PPCGGen->ctx, true);
     isl_options_set_schedule_whole_component(PPCGGen->ctx, false);
 
     isl_schedule *Schedule = get_schedule(PPCGGen);
 
     int has_permutable = has_any_permutable_node(Schedule);
 
+    Schedule =
+        isl_schedule_align_params(Schedule, S->getFullParamSpace().release());
+
     if (!has_permutable || has_permutable < 0) {
       Schedule = isl_schedule_free(Schedule);
     } else {
       Schedule = map_to_device(PPCGGen, Schedule);
       PPCGGen->tree = generate_code(PPCGGen, isl_schedule_copy(Schedule));
     }
 
     if (DumpSchedule) {

test/GPGPU/align-params-in-schedule.ll

+; RUN: opt -S -polly-process-unprofitable -polly-codegen-ppcg \
+; RUN: -polly-invariant-load-hoisting -polly-ignore-parameter-bounds < %s | \
+; RUN: FileCheck %s
+
+; CHECK: polly_launchKernel
+
+; Verify that this program compiles. At some point, this compilation crashed
+; due to insufficient parameters being available.
+
+source_filename = "bugpoint-output-4d01492.bc"
+target datalayout = "e-p:64:64:64-S128-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f16:16:16-f32:32:32-f64:64:64-f128:128:128-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
+target triple = "x86_64-unknown-linux-gnu"
+
+%struct.barney = type { i8*, i64, i64, [2 x %struct.widget] }
+%struct.widget = type { i64, i64, i64 }
+
+@global = external unnamed_addr global %struct.barney, align 32
+
+; Function Attrs: nounwind uwtable
+define void @wobble(i32* noalias %arg) #0 {
+bb:
+  %tmp = load i32, i32* %arg, align 4
+  br label %bb1
+
+bb1:                                              ; preds = %bb13, %bb
+  %tmp2 = phi i32 [ %tmp15, %bb13 ], [ 1, %bb ]
+  br label %bb3
+
+bb3:                                              ; preds = %bb3, %bb1
+  %tmp4 = load i32*, i32** bitcast (%struct.barney* @global to i32**), align 32
+  %tmp5 = sext i32 %tmp2 to i64
+  %tmp6 = load i64, i64* getelementptr inbounds (%struct.barney, %struct.barney* @global, i64 0, i32 3, i64 1, i32 0), align 8
+  %tmp7 = mul i64 %tmp6, %tmp5
+  %tmp8 = add i64 %tmp7, 0
+  %tmp9 = load i64, i64* getelementptr inbounds (%struct.barney, %struct.barney* @global, i64 0, i32 1), align 8
+  %tmp10 = add i64 %tmp8, %tmp9
+  %tmp11 = getelementptr i32, i32* %tmp4, i64 %tmp10
+  store i32 undef, i32* %tmp11, align 4
+  %tmp12 = icmp eq i32 0, 0
+  br i1 %tmp12, label %bb13, label %bb3
+
+bb13:                                             ; preds = %bb3
+  %tmp14 = icmp eq i32 %tmp2, %tmp
+  %tmp15 = add i32 %tmp2, 1
+  br i1 %tmp14, label %bb16, label %bb1
+
+bb16:                                             ; preds = %bb13
+  ret void
+}
+
+attributes #0 = { nounwind uwtable }