ldc/gen/passes/SimplifyDRuntimeCalls.cpp

//===-- SimplifyDRuntimeCalls.cpp - Optimize druntime calls ---------------===//
//
//                         LDC – the LLVM D compiler
//
// This file is distributed under the University of Illinois Open Source
// License. See the LICENSE file for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements a simple pass that applies a variety of small
// optimizations for calls to specific functions in the D runtime.
//
// The machinery was copied from the standard -simplify-libcalls LLVM pass.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "simplify-drtcalls"

#include "Passes.h"
#include "llvm/Pass.h"
#if LDC_LLVM_VER >= 303
#include "llvm/IR/Function.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/DataLayout.h"
#else
#include "llvm/Function.h"
#include "llvm/Intrinsics.h"
#if LDC_LLVM_VER == 302
#include "llvm/IRBuilder.h"
#include "llvm/DataLayout.h"
#else
#include "llvm/Support/IRBuilder.h"
#include "llvm/Target/TargetData.h"
#endif
#endif
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "gen/runtime.h"

using namespace llvm;

#if LDC_LLVM_VER < 302
typedef TargetData DataLayout;
#endif

STATISTIC(NumSimplified, "Number of runtime calls simplified");
STATISTIC(NumDeleted, "Number of runtime calls deleted");

//===----------------------------------------------------------------------===//
// Optimizer Base Class
//===----------------------------------------------------------------------===//

/// This class is the abstract base class for the set of optimizations that
/// corresponds to one library call.
namespace {
    class LLVM_LIBRARY_VISIBILITY LibCallOptimization {
    protected:
        Function *Caller;
        bool *Changed;
        const DataLayout *DL;
        AliasAnalysis *AA;
        LLVMContext *Context;

        /// CastToCStr - Return V if it is an i8*, otherwise cast it to i8*.
        Value *CastToCStr(Value *V, IRBuilder<> &B);

        /// EmitMemCpy - Emit a call to the memcpy function to the builder.  This
        /// always expects that the size has type 'intptr_t' and Dst/Src are pointers.
        Value *EmitMemCpy(Value *Dst, Value *Src, Value *Len,
                          unsigned Align, IRBuilder<> &B);
    public:
        LibCallOptimization() { }
        virtual ~LibCallOptimization() {}

        /// CallOptimizer - This pure virtual method is implemented by base classes to
        /// do various optimizations.  If this returns null then no transformation was
        /// performed.  If it returns CI, then it transformed the call and CI is to be
        /// deleted.  If it returns something else, replace CI with the new value and
        /// delete CI.
        virtual Value *CallOptimizer(Function *Callee, CallInst *CI, IRBuilder<> &B)=0;

        Value *OptimizeCall(CallInst *CI, bool& Changed, const DataLayout *DL,
                AliasAnalysis& AA, IRBuilder<> &B) {
            Caller = CI->getParent()->getParent();
            this->Changed = &Changed;
            this->DL = DL;
            this->AA = &AA;
            if (CI->getCalledFunction())
                Context = &CI->getCalledFunction()->getContext();
            return CallOptimizer(CI->getCalledFunction(), CI, B);
        }
    };
} // End anonymous namespace.

/// CastToCStr - Return V if it is an i8*, otherwise cast it to i8*.
Value *LibCallOptimization::CastToCStr(Value *V, IRBuilder<> &B) {
  return B.CreateBitCast(V, PointerType::getUnqual(B.getInt8Ty()), "cstr");
}

/// EmitMemCpy - Emit a call to the memcpy function to the builder.  This always
/// expects that the size has type 'intptr_t' and Dst/Src are pointers.
Value *LibCallOptimization::EmitMemCpy(Value *Dst, Value *Src, Value *Len,
                                       unsigned Align, IRBuilder<> &B) {
  return B.CreateMemCpy(CastToCStr(Dst, B), CastToCStr(Src, B), Len, Align, false);
}

//===----------------------------------------------------------------------===//
// Miscellaneous LibCall Optimizations
//===----------------------------------------------------------------------===//

namespace {
//===---------------------------------------===//
// '_d_arraysetlengthT'/'_d_arraysetlengthiT' Optimizations

/// ArraySetLengthOpt - remove libcall for arr.length = N if N <= arr.length
struct LLVM_LIBRARY_VISIBILITY ArraySetLengthOpt : public LibCallOptimization {
    virtual Value *CallOptimizer(Function *Callee, CallInst *CI, IRBuilder<> &B) {
        // Verify we have a reasonable prototype for _d_arraysetlength[i]T
        const FunctionType *FT = Callee->getFunctionType();
        if (Callee->arg_size() != 4 || !isa<PointerType>(FT->getReturnType()) ||
            !isa<IntegerType>(FT->getParamType(1)) ||
            FT->getParamType(1) != FT->getParamType(2) ||
            FT->getParamType(3) != FT->getReturnType())
          return 0;

        // Whether or not this allocates is irrelevant if the result isn't used.
        // Just delete if that's the case.
        if (CI->use_empty())
            return CI;

        Value* NewLen = CI->getOperand(1);
        if (Constant* NewCst = dyn_cast<Constant>(NewLen)) {
            Value* Data = CI->getOperand(3);

            // For now, we just catch the simplest of cases.
            //
            // TODO: Implement a more general way to compare old and new
            //       lengths, to catch cases like "arr.length = arr.length - 1;"
            //       (But beware of unsigned overflow! For example, we can't
            //       safely transform that example if arr.length may be 0)

            // Setting length to 0 never reallocates, so replace by data argument
            if (NewCst->isNullValue())
                return Data;

            // If both lengths are constant integers, see if NewLen <= OldLen
            Value* OldLen = CI->getOperand(2);
            if (ConstantInt* OldInt = dyn_cast<ConstantInt>(OldLen))
                if (ConstantInt* NewInt = dyn_cast<ConstantInt>(NewCst))
                    if (NewInt->getValue().ule(OldInt->getValue()))
                        return Data;
        }
        return 0;
    }
};

/// ArrayCastLenOpt - remove libcall for cast(T[]) arr if it's safe to do so.
struct LLVM_LIBRARY_VISIBILITY ArrayCastLenOpt : public LibCallOptimization {
    virtual Value *CallOptimizer(Function *Callee, CallInst *CI, IRBuilder<> &B) {
        // Verify we have a reasonable prototype for _d_array_cast_len
        const FunctionType *FT = Callee->getFunctionType();
        const Type* RetTy = FT->getReturnType();
        if (Callee->arg_size() != 3 || !isa<IntegerType>(RetTy) ||
            FT->getParamType(0) != RetTy || FT->getParamType(1) != RetTy ||
            FT->getParamType(2) != RetTy)
          return 0;

        Value* OldLen = CI->getOperand(0);
        Value* OldSize = CI->getOperand(1);
        Value* NewSize = CI->getOperand(2);

        // If the old length was zero, always return zero.
        if (Constant* LenCst = dyn_cast<Constant>(OldLen))
            if (LenCst->isNullValue())
                return OldLen;

        // Equal sizes are much faster to check for, so do so now.
        if (OldSize == NewSize)
            return OldLen;

        // If both sizes are constant integers, see if OldSize is a multiple of NewSize
        if (ConstantInt* OldInt = dyn_cast<ConstantInt>(OldSize))
            if (ConstantInt* NewInt = dyn_cast<ConstantInt>(NewSize)) {
                // Don't crash on NewSize == 0, even though it shouldn't happen.
                if (NewInt->isNullValue())
                    return 0;

                APInt Quot, Rem;
                APInt::udivrem(OldInt->getValue(), NewInt->getValue(), Quot, Rem);
                if (Rem == 0)
                    return B.CreateMul(OldLen, ConstantInt::get(*Context, Quot));
            }
        return 0;
    }
};

/// AllocationOpt - Common optimizations for various GC allocations.
struct LLVM_LIBRARY_VISIBILITY AllocationOpt : public LibCallOptimization {
    virtual Value *CallOptimizer(Function *Callee, CallInst *CI, IRBuilder<> &B) {
        // Allocations are never equal to constants, so remove any equality
        // comparisons to constants. (Most importantly comparisons to null at
        // the start of inlined member functions)
        for (CallInst::use_iterator I = CI->use_begin(), E = CI->use_end() ; I != E;) {
            Instruction* User = cast<Instruction>(*I++);

            if (ICmpInst* Cmp = dyn_cast<ICmpInst>(User)) {
                if (!Cmp->isEquality())
                    continue;
                Constant* C = 0;
                if ((C = dyn_cast<Constant>(Cmp->getOperand(0)))
                    || (C = dyn_cast<Constant>(Cmp->getOperand(1)))) {
                    Value* Result = ConstantInt::get(B.getInt1Ty(), !Cmp->isTrueWhenEqual());
                    Cmp->replaceAllUsesWith(Result);
                    // Don't delete the comparison because there may be an
                    // iterator to it. Instead, set the operands to constants
                    // and let dead code elimination clean it up later.
                    // (It doesn't matter that this changes the value of the
                    // icmp because it's not used anymore anyway)
                    Cmp->setOperand(0, C);
                    Cmp->setOperand(1, C);
                    *Changed = true;
                }
            }
        }

        // If it's not used (anymore), pre-emptively GC it.
        if (CI->use_empty())
            return CI;
        return 0;
    }
};

/// ArraySliceCopyOpt - Turn slice copies into llvm.memcpy when safe
struct LLVM_LIBRARY_VISIBILITY ArraySliceCopyOpt : public LibCallOptimization {
    virtual Value *CallOptimizer(Function *Callee, CallInst *CI, IRBuilder<> &B) {
        // Verify we have a reasonable prototype for _d_array_slice_copy
        const FunctionType *FT = Callee->getFunctionType();
        const Type* VoidPtrTy = PointerType::getUnqual(B.getInt8Ty());
        if (Callee->arg_size() != 4 || FT->getReturnType() != B.getVoidTy() ||
            FT->getParamType(0) != VoidPtrTy ||
            !isa<IntegerType>(FT->getParamType(1)) ||
            FT->getParamType(2) != VoidPtrTy ||
            FT->getParamType(3) != FT->getParamType(1))
          return 0;

        Value* Size = CI->getOperand(1);

        // Check the lengths match
        if (CI->getOperand(3) != Size)
            return 0;

        // Assume unknown size unless we have constant size (that fits in an uint)
        unsigned Sz = ~0U;
        if (ConstantInt* Int = dyn_cast<ConstantInt>(Size))
            if (Int->getValue().isIntN(32))
                Sz = Int->getValue().getZExtValue();

        // Check if the pointers may alias
        if (AA->alias(CI->getOperand(0), Sz, CI->getOperand(2), Sz))
            return 0;

        // Equal length and the pointers definitely don't alias, so it's safe to
        // replace the call with memcpy
        return EmitMemCpy(CI->getOperand(0), CI->getOperand(2), Size, 1, B);
    }
};

// TODO: More optimizations! :)

} // end anonymous namespace.

//===----------------------------------------------------------------------===//
// SimplifyDRuntimeCalls Pass Implementation
//===----------------------------------------------------------------------===//

namespace {
    /// This pass optimizes library functions from the D runtime as used by LDC.
    ///
    class LLVM_LIBRARY_VISIBILITY SimplifyDRuntimeCalls : public FunctionPass {
        StringMap<LibCallOptimization*> Optimizations;

        // Array operations
        ArraySetLengthOpt ArraySetLength;
        ArrayCastLenOpt ArrayCastLen;
        ArraySliceCopyOpt ArraySliceCopy;

        // GC allocations
        AllocationOpt Allocation;

        public:
        static char ID; // Pass identification
        SimplifyDRuntimeCalls() : FunctionPass(ID) {}

        void InitOptimizations();
        bool runOnFunction(Function &F);

        bool runOnce(Function &F, const DataLayout *DL, AliasAnalysis& AA);

        virtual void getAnalysisUsage(AnalysisUsage &AU) const {
#if LDC_LLVM_VER >= 305
          AU.addRequired<DataLayoutPass>();
#else
          AU.addRequired<DataLayout>();
#endif
          AU.addRequired<AliasAnalysis>();
        }
    };
    char SimplifyDRuntimeCalls::ID = 0;
} // end anonymous namespace.

static RegisterPass<SimplifyDRuntimeCalls>
X("simplify-drtcalls", "Simplify calls to D runtime");

// Public interface to the pass.
FunctionPass *createSimplifyDRuntimeCalls() {
  return new SimplifyDRuntimeCalls();
}

/// Optimizations - Populate the Optimizations map with all the optimizations
/// we know.
void SimplifyDRuntimeCalls::InitOptimizations() {
    // Some array-related optimizations
    Optimizations["_d_arraysetlengthT"] = &ArraySetLength;
    Optimizations["_d_arraysetlengthiT"] = &ArraySetLength;
    Optimizations["_d_array_cast_len"] = &ArrayCastLen;
    Optimizations["_d_array_slice_copy"] = &ArraySliceCopy;

    /* Delete calls to runtime functions which aren't needed if their result is
     * unused. That comes down to functions that don't do anything but
     * GC-allocate and initialize some memory.
     * We don't need to do this for functions which are marked 'readnone' or
     * 'readonly', since LLVM doesn't need our help figuring out when those can
     * be deleted.
     * (We can't mark allocating calls as readonly/readnone because they don't
     * return the same pointer every time when called with the same arguments)
     */
    Optimizations["_d_allocmemoryT"] = &Allocation;
    Optimizations["_d_newarrayT"] = &Allocation;
    Optimizations["_d_newarrayiT"] = &Allocation;
    Optimizations["_d_newarrayvT"] = &Allocation;
    Optimizations["_d_newarraymT"] = &Allocation;
    Optimizations["_d_newarraymiT"] = &Allocation;
    Optimizations["_d_newarraymvT"] = &Allocation;
    Optimizations["_d_newclass"] = &Allocation;
}


/// runOnFunction - Top level algorithm.
///
bool SimplifyDRuntimeCalls::runOnFunction(Function &F) {
    if (Optimizations.empty())
        InitOptimizations();

#if LDC_LLVM_VER >= 305
    DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
    const DataLayout *DL = DLP ? &DLP->getDataLayout() : 0;
#else
    const DataLayout *DL = &getAnalysis<DataLayout>();
#endif
    AliasAnalysis &AA = getAnalysis<AliasAnalysis>();

    // Iterate to catch opportunities opened up by other optimizations,
    // such as calls that are only used as arguments to unused calls:
    // When the second call gets deleted the first call will become unused, but
    // without iteration we wouldn't notice if we inspected the first call
    // before the second one.
    bool EverChanged = false;
    bool Changed;
    do {
        Changed = runOnce(F, DL, AA);
        EverChanged |= Changed;
    } while (Changed);

    return EverChanged;
}

bool SimplifyDRuntimeCalls::runOnce(Function &F, const DataLayout *DL, AliasAnalysis& AA) {
    IRBuilder<> Builder(F.getContext());

    bool Changed = false;
    for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
        for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
            // Ignore non-calls.
            CallInst *CI = dyn_cast<CallInst>(I++);
            if (!CI) continue;

            // Ignore indirect calls and calls to non-external functions.
            Function *Callee = CI->getCalledFunction();
            if (Callee == 0 || !Callee->isDeclaration() ||
                    !(Callee->hasExternalLinkage()
#if LDC_LLVM_VER < 305
                    || Callee->hasDLLImportLinkage()
#endif
                    ))
                continue;

            // Ignore unknown calls.
            StringMap<LibCallOptimization*>::iterator OMI =
                Optimizations.find(Callee->getName());
            if (OMI == Optimizations.end()) continue;

            DEBUG(errs() << "SimplifyDRuntimeCalls inspecting: " << *CI);

            // Set the builder to the instruction after the call.
            Builder.SetInsertPoint(BB, I);

            // Try to optimize this call.
            Value *Result = OMI->second->OptimizeCall(CI, Changed, DL, AA, Builder);
            if (Result == 0) continue;

            DEBUG(errs() << "SimplifyDRuntimeCalls simplified: " << *CI;
                  errs() << "  into: " << *Result << "\n");

            // Something changed!
            Changed = true;

            if (Result == CI) {
                assert(CI->use_empty());
                ++NumDeleted;
                AA.deleteValue(CI);
            } else {
                ++NumSimplified;
                AA.replaceWithNewValue(CI, Result);

                if (!CI->use_empty())
                    CI->replaceAllUsesWith(Result);

                if (!Result->hasName())
                    Result->takeName(CI);
            }

            // Inspect the instruction after the call (which was potentially just
            // added) next.
            I = CI; ++I;

            CI->eraseFromParent();
        }
    }
    return Changed;
}