UnrealEngine/Engine/Source/ThirdParty/Intel/ISPC/ispc-1.19.0/src/opt/InstructionSimplify.cpp

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*/

#include "InstructionSimplify.h"

namespace ispc {

char InstructionSimplifyPass::ID = 0;

static llvm::Value *lSimplifyBoolVec(llvm::Value *value) {
    llvm::TruncInst *trunc = llvm::dyn_cast<llvm::TruncInst>(value);
    if (trunc != NULL) {
        // Convert trunc({sext,zext}(i1 vector)) -> (i1 vector)
        llvm::SExtInst *sext = llvm::dyn_cast<llvm::SExtInst>(value);
        if (sext && sext->getOperand(0)->getType() == LLVMTypes::Int1VectorType)
            return sext->getOperand(0);

        llvm::ZExtInst *zext = llvm::dyn_cast<llvm::ZExtInst>(value);
        if (zext && zext->getOperand(0)->getType() == LLVMTypes::Int1VectorType)
            return zext->getOperand(0);
    }
    /*
      // This optimization has discernable benefit on the perf
      // suite on latest LLVM versions.
      // On 3.4+ (maybe even older), it can result in illegal
      // operations, so it's being disabled.
    llvm::ICmpInst *icmp = llvm::dyn_cast<llvm::ICmpInst>(value);
    if (icmp != NULL) {
        // icmp(ne, {sext,zext}(foo), zeroinitializer) -> foo
        if (icmp->getSignedPredicate() == llvm::CmpInst::ICMP_NE) {
            llvm::Value *op1 = icmp->getOperand(1);
            if (llvm::isa<llvm::ConstantAggregateZero>(op1)) {
                llvm::Value *op0 = icmp->getOperand(0);
                llvm::SExtInst *sext = llvm::dyn_cast<llvm::SExtInst>(op0);
                if (sext)
                    return sext->getOperand(0);
                llvm::ZExtInst *zext = llvm::dyn_cast<llvm::ZExtInst>(op0);
                if (zext)
                    return zext->getOperand(0);
            }
        }

    }
    */
    return NULL;
}

static bool lSimplifySelect(llvm::SelectInst *selectInst, llvm::BasicBlock::iterator iter) {
    if (selectInst->getType()->isVectorTy() == false)
        return false;
    Assert(selectInst->getOperand(1) != NULL);
    Assert(selectInst->getOperand(2) != NULL);
    llvm::Value *factor = selectInst->getOperand(0);

    // Simplify all-on or all-off mask values
    MaskStatus maskStatus = GetMaskStatusFromValue(factor);
    llvm::Value *value = NULL;
    if (maskStatus == MaskStatus::all_on)
        // Mask all on -> replace with the first select value
        value = selectInst->getOperand(1);
    else if (maskStatus == MaskStatus::all_off)
        // Mask all off -> replace with the second select value
        value = selectInst->getOperand(2);
    if (value != NULL) {
        ReplaceInstWithValueWrapper(iter, value);
        return true;
    }

    // Sometimes earlier LLVM optimization passes generate unnecessarily
    // complex expressions for the selection vector, which in turn confuses
    // the code generators and leads to sub-optimal code (particularly for
    // 8 and 16-bit masks).  We'll try to simplify them out here so that
    // the code generator patterns match..
    if ((factor = lSimplifyBoolVec(factor)) != NULL) {
        llvm::Instruction *newSelect = llvm::SelectInst::Create(factor, selectInst->getOperand(1),
                                                                selectInst->getOperand(2), selectInst->getName());
        llvm::ReplaceInstWithInst(selectInst, newSelect);
        return true;
    }

    return false;
}

static bool lSimplifyCall(llvm::CallInst *callInst, llvm::BasicBlock::iterator iter) {
    llvm::Function *calledFunc = callInst->getCalledFunction();

    // Turn a __movmsk call with a compile-time constant vector into the
    // equivalent scalar value.
    if (calledFunc == NULL || calledFunc != m->module->getFunction("__movmsk"))
        return false;

    uint64_t mask;
    if (GetMaskFromValue(callInst->getArgOperand(0), &mask) == true) {
        ReplaceInstWithValueWrapper(iter, LLVMInt64(mask));
        return true;
    }
    return false;
}

bool InstructionSimplifyPass::simplifyInstructions(llvm::BasicBlock &bb) {
    DEBUG_START_BB("InstructionSimplify");

    bool modifiedAny = false;

restart:
    for (llvm::BasicBlock::iterator iter = bb.begin(), e = bb.end(); iter != e; ++iter) {
        llvm::SelectInst *selectInst = llvm::dyn_cast<llvm::SelectInst>(&*iter);
        if (selectInst && lSimplifySelect(selectInst, iter)) {
            modifiedAny = true;
            goto restart;
        }
        llvm::CallInst *callInst = llvm::dyn_cast<llvm::CallInst>(&*iter);
        if (callInst && lSimplifyCall(callInst, iter)) {
            modifiedAny = true;
            goto restart;
        }
    }

    DEBUG_END_BB("InstructionSimplify");

    return modifiedAny;
}

bool InstructionSimplifyPass::runOnFunction(llvm::Function &F) {

    llvm::TimeTraceScope FuncScope("InstructionSimplifyPass::runOnFunction", F.getName());
    bool modifiedAny = false;
    for (llvm::BasicBlock &BB : F) {
        modifiedAny |= simplifyInstructions(BB);
    }
    return modifiedAny;
}

llvm::Pass *CreateInstructionSimplifyPass() { return new InstructionSimplifyPass; }

} // namespace ispc