[ARM] Don't convert switches to lookup tables of pointers with ROPI/RWPI

With the ROPI and RWPI relocation models we can't always have pointers
to global data or functions in constant data, so don't try to convert switches
into lookup tables if any value in the lookup table would require a relocation.
We can still safely emit lookup tables of other values, such as simple
constants.

Differential Revision: https://reviews.llvm.org/D24462

llvm-svn: 283530

3 files changed, 40 insertions, 17 deletions

diff --git a/llvm/lib/Analysis/TargetTransformInfo.cpp b/llvm/lib/Analysis/TargetTransformInfo.cpp
index 7f225a59258..fb0db03eb3f 100644
--- a/llvm/lib/Analysis/TargetTransformInfo.cpp
+++ b/llvm/lib/Analysis/TargetTransformInfo.cpp
@@ -178,6 +178,9 @@ unsigned TargetTransformInfo::getJumpBufSize() const {
 bool TargetTransformInfo::shouldBuildLookupTables() const {
   return TTIImpl->shouldBuildLookupTables();
 }
+bool TargetTransformInfo::shouldBuildLookupTablesForConstant(Constant *C) const {
+  return TTIImpl->shouldBuildLookupTablesForConstant(C);
+}
 
 bool TargetTransformInfo::enableAggressiveInterleaving(bool LoopHasReductions) const {
   return TTIImpl->enableAggressiveInterleaving(LoopHasReductions);
diff --git a/llvm/lib/Target/ARM/ARMTargetTransformInfo.h b/llvm/lib/Target/ARM/ARMTargetTransformInfo.h
index a0ca9e64800..c8b057b6aaf 100644
--- a/llvm/lib/Target/ARM/ARMTargetTransformInfo.h
+++ b/llvm/lib/Target/ARM/ARMTargetTransformInfo.h
@@ -128,6 +128,16 @@ public:
   int getInterleavedMemoryOpCost(unsigned Opcode, Type *VecTy, unsigned Factor,
                                  ArrayRef<unsigned> Indices, unsigned Alignment,
                                  unsigned AddressSpace);
+
+  bool shouldBuildLookupTablesForConstant(Constant *C) const {
+    // In the ROPI and RWPI relocation models we can't have pointers to global
+    // variables or functions in constant data, so don't convert switches to
+    // lookup tables if any of the values would need relocation.
+    if (ST->isROPI() || ST->isRWPI())
+      return !C->needsRelocation();
+
+    return true;
+  }
   /// @}
 };
 
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 1546a60c337..63b9f4061f2 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -4425,18 +4425,25 @@ static bool ForwardSwitchConditionToPHI(SwitchInst *SI) {
 
 /// Return true if the backend will be able to handle
 /// initializing an array of constants like C.
-static bool ValidLookupTableConstant(Constant *C) {
+static bool ValidLookupTableConstant(Constant *C, const TargetTransformInfo &TTI) {
   if (C->isThreadDependent())
     return false;
   if (C->isDLLImportDependent())
     return false;
 
+  if (!isa<ConstantFP>(C) && !isa<ConstantInt>(C) &&
+      !isa<ConstantPointerNull>(C) && !isa<GlobalValue>(C) &&
+      !isa<UndefValue>(C) && !isa<ConstantExpr>(C))
+    return false;
+
   if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C))
-    return CE->isGEPWithNoNotionalOverIndexing();
+    if (!CE->isGEPWithNoNotionalOverIndexing())
+      return false;
 
-  return isa<ConstantFP>(C) || isa<ConstantInt>(C) ||
-         isa<ConstantPointerNull>(C) || isa<GlobalValue>(C) ||
-         isa<UndefValue>(C);
+  if (!TTI.shouldBuildLookupTablesForConstant(C))
+    return false;
+
+  return true;
 }
 
 /// If V is a Constant, return it. Otherwise, try to look up
@@ -4490,8 +4497,8 @@ ConstantFold(Instruction *I, const DataLayout &DL,
 static bool
 GetCaseResults(SwitchInst *SI, ConstantInt *CaseVal, BasicBlock *CaseDest,
                BasicBlock **CommonDest,
-               SmallVectorImpl<std::pair<PHINode *, Constant *>> &Res,
-               const DataLayout &DL) {
+               SmallVectorImpl<std::pair<PHINode *, Constant *> > &Res,
+               const DataLayout &DL, const TargetTransformInfo &TTI) {
   // The block from which we enter the common destination.
   BasicBlock *Pred = SI->getParent();
 
@@ -4553,7 +4560,7 @@ GetCaseResults(SwitchInst *SI, ConstantInt *CaseVal, BasicBlock *CaseDest,
       return false;
 
     // Be conservative about which kinds of constants we support.
-    if (!ValidLookupTableConstant(ConstVal))
+    if (!ValidLookupTableConstant(ConstVal, TTI))
       return false;
 
     Res.push_back(std::make_pair(PHI, ConstVal));
@@ -4585,14 +4592,15 @@ static bool InitializeUniqueCases(SwitchInst *SI, PHINode *&PHI,
                                   BasicBlock *&CommonDest,
                                   SwitchCaseResultVectorTy &UniqueResults,
                                   Constant *&DefaultResult,
-                                  const DataLayout &DL) {
+                                  const DataLayout &DL,
+                                  const TargetTransformInfo &TTI) {
   for (auto &I : SI->cases()) {
     ConstantInt *CaseVal = I.getCaseValue();
 
     // Resulting value at phi nodes for this case value.
     SwitchCaseResultsTy Results;
     if (!GetCaseResults(SI, CaseVal, I.getCaseSuccessor(), &CommonDest, Results,
-                        DL))
+                        DL, TTI))
       return false;
 
     // Only one value per case is permitted
@@ -4610,7 +4618,7 @@ static bool InitializeUniqueCases(SwitchInst *SI, PHINode *&PHI,
   SmallVector<std::pair<PHINode *, Constant *>, 1> DefaultResults;
   BasicBlock *DefaultDest = SI->getDefaultDest();
   GetCaseResults(SI, nullptr, SI->getDefaultDest(), &CommonDest, DefaultResults,
-                 DL);
+                 DL, TTI);
   // If the default value is not found abort unless the default destination
   // is unreachable.
   DefaultResult =
@@ -4689,7 +4697,8 @@ static void RemoveSwitchAfterSelectConversion(SwitchInst *SI, PHINode *PHI,
 /// phi nodes in a common successor block with only two different
 /// constant values, replace the switch with select.
 static bool SwitchToSelect(SwitchInst *SI, IRBuilder<> &Builder,
-                           AssumptionCache *AC, const DataLayout &DL) {
+                           AssumptionCache *AC, const DataLayout &DL,
+                           const TargetTransformInfo &TTI) {
   Value *const Cond = SI->getCondition();
   PHINode *PHI = nullptr;
   BasicBlock *CommonDest = nullptr;
@@ -4697,7 +4706,7 @@ static bool SwitchToSelect(SwitchInst *SI, IRBuilder<> &Builder,
   SwitchCaseResultVectorTy UniqueResults;
   // Collect all the cases that will deliver the same value from the switch.
   if (!InitializeUniqueCases(SI, PHI, CommonDest, UniqueResults, DefaultResult,
-                             DL))
+                             DL, TTI))
     return false;
   // Selects choose between maximum two values.
   if (UniqueResults.size() != 2)
@@ -5135,7 +5144,7 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
     typedef SmallVector<std::pair<PHINode *, Constant *>, 4> ResultsTy;
     ResultsTy Results;
     if (!GetCaseResults(SI, CaseVal, CI.getCaseSuccessor(), &CommonDest,
-                        Results, DL))
+                        Results, DL, TTI))
       return false;
 
     // Append the result from this case to the list for each phi.
@@ -5161,8 +5170,9 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
   // If the table has holes, we need a constant result for the default case
   // or a bitmask that fits in a register.
   SmallVector<std::pair<PHINode *, Constant *>, 4> DefaultResultsList;
-  bool HasDefaultResults = GetCaseResults(SI, nullptr, SI->getDefaultDest(),
-                                          &CommonDest, DefaultResultsList, DL);
+  bool HasDefaultResults =
+      GetCaseResults(SI, nullptr, SI->getDefaultDest(), &CommonDest,
+                     DefaultResultsList, DL, TTI);
 
   bool NeedMask = (TableHasHoles && !HasDefaultResults);
   if (NeedMask) {
@@ -5458,7 +5468,7 @@ bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
   if (EliminateDeadSwitchCases(SI, AC, DL))
     return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
 
-  if (SwitchToSelect(SI, Builder, AC, DL))
+  if (SwitchToSelect(SI, Builder, AC, DL, TTI))
     return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
 
   if (ForwardSwitchConditionToPHI(SI))