C++ (Cpp) GenTree::GetVN Examples

Example #1

File: copyprop.cpp Project: AndyAyersMS/coreclr

void Compiler::optCopyProp(BasicBlock* block, GenTree* stmt, GenTree* tree, LclNumToGenTreePtrStack* curSsaName)
{
    // TODO-Review: EH successor/predecessor iteration seems broken.
    if (block->bbCatchTyp == BBCT_FINALLY || block->bbCatchTyp == BBCT_FAULT)
    {
        return;
    }

    // If not local nothing to do.
    if (!tree->IsLocal())
    {
        return;
    }
    if (tree->OperGet() == GT_PHI_ARG || tree->OperGet() == GT_LCL_FLD)
    {
        return;
    }

    // Propagate only on uses.
    if (tree->gtFlags & GTF_VAR_DEF)
    {
        return;
    }
    unsigned lclNum = tree->AsLclVarCommon()->GetLclNum();

    // Skip non-SSA variables.
    if (!lvaInSsa(lclNum))
    {
        return;
    }

    assert(tree->gtVNPair.GetConservative() != ValueNumStore::NoVN);

    for (LclNumToGenTreePtrStack::KeyIterator iter = curSsaName->Begin(); !iter.Equal(curSsaName->End()); ++iter)
    {
        unsigned newLclNum = iter.Get();

        GenTree* op = iter.GetValue()->Index(0);

        // Nothing to do if same.
        if (lclNum == newLclNum)
        {
            continue;
        }

        // Skip variables with assignments embedded in the statement (i.e., with a comma). Because we
        // are not currently updating their SSA names as live in the copy-prop pass of the stmt.
        if (VarSetOps::IsMember(this, optCopyPropKillSet, lvaTable[newLclNum].lvVarIndex))
        {
            continue;
        }

        if (op->gtFlags & GTF_VAR_CAST)
        {
            continue;
        }
        if (gsShadowVarInfo != nullptr && lvaTable[newLclNum].lvIsParam &&
            gsShadowVarInfo[newLclNum].shadowCopy == lclNum)
        {
            continue;
        }
        ValueNum opVN = GetUseAsgDefVNOrTreeVN(op);
        if (opVN == ValueNumStore::NoVN)
        {
            continue;
        }
        if (op->TypeGet() != tree->TypeGet())
        {
            continue;
        }
        if (opVN != tree->gtVNPair.GetConservative())
        {
            continue;
        }
        if (optCopyProp_LclVarScore(&lvaTable[lclNum], &lvaTable[newLclNum], true) <= 0)
        {
            continue;
        }
        // Check whether the newLclNum is live before being substituted. Otherwise, we could end
        // up in a situation where there must've been a phi node that got pruned because the variable
        // is not live anymore. For example,
        //  if
        //     x0 = 1
        //  else
        //     x1 = 2
        //  print(c) <-- x is not live here. Let's say 'c' shares the value number with "x0."
        //
        // If we simply substituted 'c' with "x0", we would be wrong. Ideally, there would be a phi
        // node x2 = phi(x0, x1) which can then be used to substitute 'c' with. But because of pruning
        // there would be no such phi node. To solve this we'll check if 'x' is live, before replacing
        // 'c' with 'x.'
        if (!lvaTable[newLclNum].lvVerTypeInfo.IsThisPtr())
        {
            if (lvaTable[newLclNum].lvAddrExposed)
            {
                continue;
            }

            // We compute liveness only on tracked variables. So skip untracked locals.
            if (!lvaTable[newLclNum].lvTracked)
            {
                continue;
            }

            // Because of this dependence on live variable analysis, CopyProp phase is immediately
            // after Liveness, SSA and VN.
            if (!VarSetOps::IsMember(this, compCurLife, lvaTable[newLclNum].lvVarIndex))
            {
                continue;
            }
        }
        unsigned newSsaNum = SsaConfig::RESERVED_SSA_NUM;
        if (op->gtFlags & GTF_VAR_DEF)
        {
            newSsaNum = GetSsaNumForLocalVarDef(op);
        }
        else // parameters, this pointer etc.
        {
            newSsaNum = op->AsLclVarCommon()->GetSsaNum();
        }

        if (newSsaNum == SsaConfig::RESERVED_SSA_NUM)
        {
            continue;
        }

#ifdef DEBUG
        if (verbose)
        {
            JITDUMP("VN based copy assertion for ");
            printTreeID(tree);
            printf(" V%02d @%08X by ", lclNum, tree->GetVN(VNK_Conservative));
            printTreeID(op);
            printf(" V%02d @%08X.\n", newLclNum, op->GetVN(VNK_Conservative));
            gtDispTree(tree, nullptr, nullptr, true);
        }
#endif

        tree->gtLclVarCommon.SetLclNum(newLclNum);
        tree->AsLclVarCommon()->SetSsaNum(newSsaNum);
        gtUpdateSideEffects(stmt, tree);
#ifdef DEBUG
        if (verbose)
        {
            printf("copy propagated to:\n");
            gtDispTree(tree, nullptr, nullptr, true);
        }
#endif
        break;
    }
    return;
}