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JIT: handle some side effects in box pattern match #1741

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Merged
AndyAyersMS merged 1 commit into from
Jan 15, 2020
Merged

JIT: handle some side effects in box pattern match #1741

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38 changes: 35 additions & 3 deletions src/coreclr/src/jit/importer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5815,6 +5815,9 @@ GenTree* Compiler::impImportLdvirtftn(GenTree* thisPtr,
// Return Value:
// Number of IL bytes matched and imported, -1 otherwise
//
// Notes:
// pResolvedToken is known to be a value type; ref type boxing
// is handled in the CEE_BOX clause.

int Compiler::impBoxPatternMatch(CORINFO_RESOLVED_TOKEN* pResolvedToken, const BYTE* codeAddr, const BYTE* codeEndp)
{
Expand Down Expand Up @@ -5854,15 +5857,44 @@ int Compiler::impBoxPatternMatch(CORINFO_RESOLVED_TOKEN* pResolvedToken, const B
// box + br_true/false
if ((codeAddr + ((codeAddr[0] >= CEE_BRFALSE) ? 5 : 2)) <= codeEndp)
{
if (!(impStackTop().val->gtFlags & GTF_SIDE_EFFECT))
GenTree* const treeToBox = impStackTop().val;
bool canOptimize = true;
GenTree* treeToNullcheck = nullptr;

// Can the thing being boxed cause a side effect?
if ((treeToBox->gtFlags & GTF_SIDE_EFFECT) != 0)
{
// Is this a side effect we can replicate cheaply?
if (((treeToBox->gtFlags & GTF_SIDE_EFFECT) == GTF_EXCEPT) &&
treeToBox->OperIs(GT_OBJ, GT_BLK, GT_IND))
{
// Yes, we just need to perform a null check.
treeToNullcheck = treeToBox->AsOp()->gtOp1;
}
else
{
canOptimize = false;
}
}

if (canOptimize)
{
CorInfoHelpFunc boxHelper = info.compCompHnd->getBoxHelper(pResolvedToken->hClass);
if (boxHelper == CORINFO_HELP_BOX)
{
JITDUMP("\n Importing BOX; BR_TRUE/FALSE as constant\n");
JITDUMP("\n Importing BOX; BR_TRUE/FALSE as %sconstant\n",
treeToNullcheck == nullptr ? "" : "nullcheck+");
impPopStack();

impPushOnStack(gtNewIconNode(1), typeInfo(TI_INT));
GenTree* result = gtNewIconNode(1);

if (treeToNullcheck != nullptr)
{
GenTree* nullcheck = gtNewOperNode(GT_NULLCHECK, TYP_I_IMPL, treeToNullcheck);
result = gtNewOperNode(GT_COMMA, TYP_INT, nullcheck, result);
}

impPushOnStack(result, typeInfo(TI_INT));
return 0;
}
}
Expand Down