[SimplifyCFG] cleanup code for converting switch to select (NFC)

This renames functions for more general usage (and current capitalization style)
before a proposed logic change in D122485.

Differential Revision: https://reviews.llvm.org/D123614

Author: rotateright

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

@@ -5531,7 +5531,7 @@ ConstantFold(Instruction *I, const DataLayout &DL,
 /// destionations CaseDest corresponding to value CaseVal (0 for the default
 /// case), of a switch instruction SI.
 static bool
-GetCaseResults(SwitchInst *SI, ConstantInt *CaseVal, BasicBlock *CaseDest,
+getCaseResults(SwitchInst *SI, ConstantInt *CaseVal, BasicBlock *CaseDest,
                BasicBlock **CommonDest,
                SmallVectorImpl<std::pair<PHINode *, Constant *>> &Res,
                const DataLayout &DL, const TargetTransformInfo &TTI) {
@@ -5602,7 +5602,7 @@ GetCaseResults(SwitchInst *SI, ConstantInt *CaseVal, BasicBlock *CaseDest,
 
 // Helper function used to add CaseVal to the list of cases that generate
 // Result. Returns the updated number of cases that generate this result.
-static uintptr_t MapCaseToResult(ConstantInt *CaseVal,
+static uintptr_t mapCaseToResult(ConstantInt *CaseVal,
                                  SwitchCaseResultVectorTy &UniqueResults,
                                  Constant *Result) {
   for (auto &I : UniqueResults) {
@@ -5621,7 +5621,7 @@ static uintptr_t MapCaseToResult(ConstantInt *CaseVal,
 // instruction. Returns false if multiple PHI nodes have been found or if
 // there is not a common destination block for the switch.
 static bool
-InitializeUniqueCases(SwitchInst *SI, PHINode *&PHI, BasicBlock *&CommonDest,
+initializeUniqueCases(SwitchInst *SI, PHINode *&PHI, BasicBlock *&CommonDest,
                       SwitchCaseResultVectorTy &UniqueResults,
                       Constant *&DefaultResult, const DataLayout &DL,
                       const TargetTransformInfo &TTI,
@@ -5631,7 +5631,7 @@ InitializeUniqueCases(SwitchInst *SI, PHINode *&PHI, BasicBlock *&CommonDest,
 
     // Resulting value at phi nodes for this case value.
     SwitchCaseResultsTy Results;
-    if (!GetCaseResults(SI, CaseVal, I.getCaseSuccessor(), &CommonDest, Results,
+    if (!getCaseResults(SI, CaseVal, I.getCaseSuccessor(), &CommonDest, Results,
                         DL, TTI))
       return false;
 
@@ -5641,7 +5641,7 @@ InitializeUniqueCases(SwitchInst *SI, PHINode *&PHI, BasicBlock *&CommonDest,
 
     // Add the case->result mapping to UniqueResults.
     const uintptr_t NumCasesForResult =
-        MapCaseToResult(CaseVal, UniqueResults, Results.begin()->second);
+        mapCaseToResult(CaseVal, UniqueResults, Results.begin()->second);
 
     // Early out if there are too many cases for this result.
     if (NumCasesForResult > MaxCasesPerResult)
@@ -5660,7 +5660,7 @@ InitializeUniqueCases(SwitchInst *SI, PHINode *&PHI, BasicBlock *&CommonDest,
   // Find the default result value.
   SmallVector<std::pair<PHINode *, Constant *>, 1> DefaultResults;
   BasicBlock *DefaultDest = SI->getDefaultDest();
-  GetCaseResults(SI, nullptr, SI->getDefaultDest(), &CommonDest, DefaultResults,
+  getCaseResults(SI, nullptr, SI->getDefaultDest(), &CommonDest, DefaultResults,
                  DL, TTI);
   // If the default value is not found abort unless the default destination
   // is unreachable.
@@ -5684,9 +5684,10 @@ InitializeUniqueCases(SwitchInst *SI, PHINode *&PHI, BasicBlock *&CommonDest,
 //   default:
 //     return 4;
 // }
-static Value *ConvertTwoCaseSwitch(const SwitchCaseResultVectorTy &ResultVector,
-                                   Constant *DefaultResult, Value *Condition,
-                                   IRBuilder<> &Builder) {
+// TODO: Handle switches with more than 2 cases that map to the same result.
+static Value *foldSwitchToSelect(const SwitchCaseResultVectorTy &ResultVector,
+                                 Constant *DefaultResult, Value *Condition,
+                                 IRBuilder<> &Builder) {
   // If we are selecting between only two cases transform into a simple
   // select or a two-way select if default is possible.
   if (ResultVector.size() == 2 && ResultVector[0].second.size() == 1 &&
@@ -5724,10 +5725,10 @@ static Value *ConvertTwoCaseSwitch(const SwitchCaseResultVectorTy &ResultVector,
 
 // Helper function to cleanup a switch instruction that has been converted into
 // a select, fixing up PHI nodes and basic blocks.
-static void RemoveSwitchAfterSelectConversion(SwitchInst *SI, PHINode *PHI,
-                                              Value *SelectValue,
-                                              IRBuilder<> &Builder,
-                                              DomTreeUpdater *DTU) {
+static void removeSwitchAfterSelectFold(SwitchInst *SI, PHINode *PHI,
+                                        Value *SelectValue,
+                                        IRBuilder<> &Builder,
+                                        DomTreeUpdater *DTU) {
   std::vector<DominatorTree::UpdateType> Updates;
 
   BasicBlock *SelectBB = SI->getParent();
@@ -5758,33 +5759,32 @@ static void RemoveSwitchAfterSelectConversion(SwitchInst *SI, PHINode *PHI,
     DTU->applyUpdates(Updates);
 }
 
-/// If the switch is only used to initialize one or more
-/// 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,
-                           DomTreeUpdater *DTU, const DataLayout &DL,
-                           const TargetTransformInfo &TTI) {
+/// If a switch is only used to initialize one or more phi nodes in a common
+/// successor block with only two different constant values, try to replace the
+/// switch with a select. Returns true if the fold was made.
+static bool trySwitchToSelect(SwitchInst *SI, IRBuilder<> &Builder,
+                              DomTreeUpdater *DTU, const DataLayout &DL,
+                              const TargetTransformInfo &TTI) {
   Value *const Cond = SI->getCondition();
   PHINode *PHI = nullptr;
   BasicBlock *CommonDest = nullptr;
   Constant *DefaultResult;
   SwitchCaseResultVectorTy UniqueResults;
   // Collect all the cases that will deliver the same value from the switch.
-  if (!InitializeUniqueCases(SI, PHI, CommonDest, UniqueResults, DefaultResult,
-                             DL, TTI, /*MaxUniqueResults*/2,
-                             /*MaxCasesPerResult*/2))
+  if (!initializeUniqueCases(SI, PHI, CommonDest, UniqueResults, DefaultResult,
+                             DL, TTI, /*MaxUniqueResults*/ 2,
+                             /*MaxCasesPerResult*/ 2))
     return false;
-  assert(PHI != nullptr && "PHI for value select not found");
 
+  assert(PHI != nullptr && "PHI for value select not found");
   Builder.SetInsertPoint(SI);
   Value *SelectValue =
-      ConvertTwoCaseSwitch(UniqueResults, DefaultResult, Cond, Builder);
-  if (SelectValue) {
-    RemoveSwitchAfterSelectConversion(SI, PHI, SelectValue, Builder, DTU);
-    return true;
-  }
-  // The switch couldn't be converted into a select.
-  return false;
+      foldSwitchToSelect(UniqueResults, DefaultResult, Cond, Builder);
+  if (!SelectValue)
+    return false;
+
+  removeSwitchAfterSelectFold(SI, PHI, SelectValue, Builder, DTU);
+  return true;
 }
 
 namespace {
@@ -6237,7 +6237,7 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
     // Resulting value at phi nodes for this case value.
     using ResultsTy = SmallVector<std::pair<PHINode *, Constant *>, 4>;
     ResultsTy Results;
-    if (!GetCaseResults(SI, CaseVal, CI->getCaseSuccessor(), &CommonDest,
+    if (!getCaseResults(SI, CaseVal, CI->getCaseSuccessor(), &CommonDest,
                         Results, DL, TTI))
       return false;
 
@@ -6265,7 +6265,7 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
   // or a bitmask that fits in a register.
   SmallVector<std::pair<PHINode *, Constant *>, 4> DefaultResultsList;
   bool HasDefaultResults =
-      GetCaseResults(SI, nullptr, SI->getDefaultDest(), &CommonDest,
+      getCaseResults(SI, nullptr, SI->getDefaultDest(), &CommonDest,
                      DefaultResultsList, DL, TTI);
 
   bool NeedMask = (TableHasHoles && !HasDefaultResults);
@@ -6569,7 +6569,7 @@ bool SimplifyCFGOpt::simplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
   if (eliminateDeadSwitchCases(SI, DTU, Options.AC, DL))
     return requestResimplify();
 
-  if (switchToSelect(SI, Builder, DTU, DL, TTI))
+  if (trySwitchToSelect(SI, Builder, DTU, DL, TTI))
     return requestResimplify();
 
   if (Options.ForwardSwitchCondToPhi && ForwardSwitchConditionToPHI(SI))