lib/Transforms/Scalar/SimplifyHalfPowrLibCalls.cpp

   1 //===- SimplifyHalfPowrLibCalls.cpp - Optimize specific half_powr calls ---===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file implements a simple pass that applies an experimental
  11 // transformation on calls to specific functions.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #define DEBUG_TYPE "simplify-libcalls-halfpowr"
  16 #include "llvm/Transforms/Scalar.h"
  17 #include "llvm/Instructions.h"
  18 #include "llvm/Intrinsics.h"
  19 #include "llvm/Module.h"
  20 #include "llvm/Pass.h"
  21 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  22 #include "llvm/Transforms/Utils/Cloning.h"
  23 #include "llvm/Target/TargetData.h"
  24 #include "llvm/ADT/STLExtras.h"
  25 #include "llvm/Support/Debug.h"
  26 using namespace llvm;
  27
  28 namespace {
  29   /// This pass optimizes well half_powr function calls.
  30   ///
  31   class SimplifyHalfPowrLibCalls : public FunctionPass {
  32     const TargetData *TD;
  33   public:
  34     static char ID; // Pass identification
  35     SimplifyHalfPowrLibCalls() : FunctionPass(&ID) {}
  36
  37     bool runOnFunction(Function &F);
  38
  39     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  40     }
  41
  42     Instruction *
  43     InlineHalfPowrs(const std::vector<Instruction *> &HalfPowrs,
  44                     Instruction *InsertPt);
  45   };
  46   char SimplifyHalfPowrLibCalls::ID = 0;
  47 } // end anonymous namespace.
  48
  49 INITIALIZE_PASS(SimplifyHalfPowrLibCalls, "simplify-libcalls-halfpowr",
  50                 "Simplify half_powr library calls", false, false);
  51
  52 // Public interface to the Simplify HalfPowr LibCalls pass.
  53 FunctionPass *llvm::createSimplifyHalfPowrLibCallsPass() {
  54   return new SimplifyHalfPowrLibCalls();
  55 }
  56
  57 /// InlineHalfPowrs - Inline a sequence of adjacent half_powr calls, rearranging
  58 /// their control flow to better facilitate subsequent optimization.
  59 Instruction *
  60 SimplifyHalfPowrLibCalls::
  61 InlineHalfPowrs(const std::vector<Instruction *> &HalfPowrs,
  62                 Instruction *InsertPt) {
  63   std::vector<BasicBlock *> Bodies;
  64   BasicBlock *NewBlock = 0;
  65
  66   for (unsigned i = 0, e = HalfPowrs.size(); i != e; ++i) {
  67     CallInst *Call = cast<CallInst>(HalfPowrs[i]);
  68     Function *Callee = Call->getCalledFunction();
  69
  70     // Minimally sanity-check the CFG of half_powr to ensure that it contains
  71     // the kind of code we expect.  If we're running this pass, we have
  72     // reason to believe it will be what we expect.
  73     Function::iterator I = Callee->begin();
  74     BasicBlock *Prologue = I++;
  75     if (I == Callee->end()) break;
  76     BasicBlock *SubnormalHandling = I++;
  77     if (I == Callee->end()) break;
  78     BasicBlock *Body = I++;
  79     if (I != Callee->end()) break;
  80     if (SubnormalHandling->getSinglePredecessor() != Prologue)
  81       break;
  82     BranchInst *PBI = dyn_cast<BranchInst>(Prologue->getTerminator());
  83     if (!PBI || !PBI->isConditional())
  84       break;
  85     BranchInst *SNBI = dyn_cast<BranchInst>(SubnormalHandling->getTerminator());
  86     if (!SNBI || SNBI->isConditional())
  87       break;
  88     if (!isa<ReturnInst>(Body->getTerminator()))
  89       break;
  90
  91     Instruction *NextInst = llvm::next(BasicBlock::iterator(Call));
  92
  93     // Inline the call, taking care of what code ends up where.
  94     NewBlock = SplitBlock(NextInst->getParent(), NextInst, this);
  95
  96     InlineFunctionInfo IFI(0, TD);
  97     bool B = InlineFunction(Call, IFI);
  98     assert(B && "half_powr didn't inline?"); B=B;
  99
 100     BasicBlock *NewBody = NewBlock->getSinglePredecessor();
 101     assert(NewBody);
 102     Bodies.push_back(NewBody);
 103   }
 104
 105   if (!NewBlock)
 106     return InsertPt;
 107
 108   // Put the code for all the bodies into one block, to facilitate
 109   // subsequent optimization.
 110   (void)SplitEdge(NewBlock->getSinglePredecessor(), NewBlock, this);
 111   for (unsigned i = 0, e = Bodies.size(); i != e; ++i) {
 112     BasicBlock *Body = Bodies[i];
 113     Instruction *FNP = Body->getFirstNonPHI();
 114     // Splice the insts from body into NewBlock.
 115     NewBlock->getInstList().splice(NewBlock->begin(), Body->getInstList(),
 116                                    FNP, Body->getTerminator());
 117   }
 118
 119   return NewBlock->begin();
 120 }
 121
 122 /// runOnFunction - Top level algorithm.
 123 ///
 124 bool SimplifyHalfPowrLibCalls::runOnFunction(Function &F) {
 125   TD = getAnalysisIfAvailable<TargetData>();
 126
 127   bool Changed = false;
 128   std::vector<Instruction *> HalfPowrs;
 129   for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
 130     for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
 131       // Look for calls.
 132       bool IsHalfPowr = false;
 133       if (CallInst *CI = dyn_cast<CallInst>(I)) {
 134         // Look for direct calls and calls to non-external functions.
 135         Function *Callee = CI->getCalledFunction();
 136         if (Callee && Callee->hasExternalLinkage()) {
 137           // Look for calls with well-known names.
 138           if (Callee->getName() == "__half_powrf4")
 139             IsHalfPowr = true;
 140         }
 141       }
 142       if (IsHalfPowr)
 143         HalfPowrs.push_back(I);
 144       // We're looking for sequences of up to three such calls, which we'll
 145       // simplify as a group.
 146       if ((!IsHalfPowr && !HalfPowrs.empty()) || HalfPowrs.size() == 3) {
 147         I = InlineHalfPowrs(HalfPowrs, I);
 148         E = I->getParent()->end();
 149         HalfPowrs.clear();
 150         Changed = true;
 151       }
 152     }
 153     assert(HalfPowrs.empty() && "Block had no terminator!");
 154   }
 155
 156   return Changed;
 157 }