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       initializeSimplifyHalfPowrLibCallsPass(*PassRegistry::getPassRegistry());
  37     }
  38
  39     bool runOnFunction(Function &F);
  40
  41     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  42     }
  43
  44     Instruction *
  45     InlineHalfPowrs(const std::vector<Instruction *> &HalfPowrs,
  46                     Instruction *InsertPt);
  47   };
  48   char SimplifyHalfPowrLibCalls::ID = 0;
  49 } // end anonymous namespace.
  50
  51 INITIALIZE_PASS(SimplifyHalfPowrLibCalls, "simplify-libcalls-halfpowr",
  52                 "Simplify half_powr library calls", false, false)
  53
  54 // Public interface to the Simplify HalfPowr LibCalls pass.
  55 FunctionPass *llvm::createSimplifyHalfPowrLibCallsPass() {
  56   return new SimplifyHalfPowrLibCalls();
  57 }
  58
  59 /// InlineHalfPowrs - Inline a sequence of adjacent half_powr calls, rearranging
  60 /// their control flow to better facilitate subsequent optimization.
  61 Instruction *
  62 SimplifyHalfPowrLibCalls::
  63 InlineHalfPowrs(const std::vector<Instruction *> &HalfPowrs,
  64                 Instruction *InsertPt) {
  65   std::vector<BasicBlock *> Bodies;
  66   BasicBlock *NewBlock = 0;
  67
  68   for (unsigned i = 0, e = HalfPowrs.size(); i != e; ++i) {
  69     CallInst *Call = cast<CallInst>(HalfPowrs[i]);
  70     Function *Callee = Call->getCalledFunction();
  71
  72     // Minimally sanity-check the CFG of half_powr to ensure that it contains
  73     // the kind of code we expect.  If we're running this pass, we have
  74     // reason to believe it will be what we expect.
  75     Function::iterator I = Callee->begin();
  76     BasicBlock *Prologue = I++;
  77     if (I == Callee->end()) break;
  78     BasicBlock *SubnormalHandling = I++;
  79     if (I == Callee->end()) break;
  80     BasicBlock *Body = I++;
  81     if (I != Callee->end()) break;
  82     if (SubnormalHandling->getSinglePredecessor() != Prologue)
  83       break;
  84     BranchInst *PBI = dyn_cast<BranchInst>(Prologue->getTerminator());
  85     if (!PBI || !PBI->isConditional())
  86       break;
  87     BranchInst *SNBI = dyn_cast<BranchInst>(SubnormalHandling->getTerminator());
  88     if (!SNBI || SNBI->isConditional())
  89       break;
  90     if (!isa<ReturnInst>(Body->getTerminator()))
  91       break;
  92
  93     Instruction *NextInst = llvm::next(BasicBlock::iterator(Call));
  94
  95     // Inline the call, taking care of what code ends up where.
  96     NewBlock = SplitBlock(NextInst->getParent(), NextInst, this);
  97
  98     InlineFunctionInfo IFI(0, TD);
  99     bool B = InlineFunction(Call, IFI);
 100     assert(B && "half_powr didn't inline?"); B=B;
 101
 102     BasicBlock *NewBody = NewBlock->getSinglePredecessor();
 103     assert(NewBody);
 104     Bodies.push_back(NewBody);
 105   }
 106
 107   if (!NewBlock)
 108     return InsertPt;
 109
 110   // Put the code for all the bodies into one block, to facilitate
 111   // subsequent optimization.
 112   (void)SplitEdge(NewBlock->getSinglePredecessor(), NewBlock, this);
 113   for (unsigned i = 0, e = Bodies.size(); i != e; ++i) {
 114     BasicBlock *Body = Bodies[i];
 115     Instruction *FNP = Body->getFirstNonPHI();
 116     // Splice the insts from body into NewBlock.
 117     NewBlock->getInstList().splice(NewBlock->begin(), Body->getInstList(),
 118                                    FNP, Body->getTerminator());
 119   }
 120
 121   return NewBlock->begin();
 122 }
 123
 124 /// runOnFunction - Top level algorithm.
 125 ///
 126 bool SimplifyHalfPowrLibCalls::runOnFunction(Function &F) {
 127   TD = getAnalysisIfAvailable<TargetData>();
 128
 129   bool Changed = false;
 130   std::vector<Instruction *> HalfPowrs;
 131   for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
 132     for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
 133       // Look for calls.
 134       bool IsHalfPowr = false;
 135       if (CallInst *CI = dyn_cast<CallInst>(I)) {
 136         // Look for direct calls and calls to non-external functions.
 137         Function *Callee = CI->getCalledFunction();
 138         if (Callee && Callee->hasExternalLinkage()) {
 139           // Look for calls with well-known names.
 140           if (Callee->getName() == "__half_powrf4")
 141             IsHalfPowr = true;
 142         }
 143       }
 144       if (IsHalfPowr)
 145         HalfPowrs.push_back(I);
 146       // We're looking for sequences of up to three such calls, which we'll
 147       // simplify as a group.
 148       if ((!IsHalfPowr && !HalfPowrs.empty()) || HalfPowrs.size() == 3) {
 149         I = InlineHalfPowrs(HalfPowrs, I);
 150         E = I->getParent()->end();
 151         HalfPowrs.clear();
 152         Changed = true;
 153       }
 154     }
 155     assert(HalfPowrs.empty() && "Block had no terminator!");
 156   }
 157
 158   return Changed;
 159 }