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Optimize Math.Pow(x, c) in JIT #26552

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Optimize Math.Pow(x, c) in JIT #26552

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d6eb0a3
Morph CALL Math.Pow(x, w) to X * X
EgorBo Sep 5, 2019
4055a1f
detect Math.Pow via CORINFO_INTRINSIC_Pow
EgorBo Sep 5, 2019
f7bd9b4
Oops, the second argument is not always a DblCon
EgorBo Sep 6, 2019
293550d
Replace gtArgEntryByArgNum(call, 1)->node with just arg1
EgorBo Sep 6, 2019
6f59c34
Fix case when both arguments are constants
EgorBo Sep 6, 2019
d43393b
fix formatting issue
EgorBo Sep 6, 2019
c99e6de
Limit usage to LCL_VAR
EgorBo Sep 6, 2019
c447729
Handle fields as arg0
EgorBo Sep 6, 2019
b2c2598
make sure GT_IND contains LCL_VAR
EgorBo Sep 6, 2019
832dda9
remove extraneous parentheses
EgorBo Sep 6, 2019
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2 changes: 2 additions & 0 deletions src/jit/importer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3580,6 +3580,8 @@ GenTree* Compiler::impIntrinsic(GenTree* newobjThis,
case CORINFO_INTRINSIC_Ceiling:
case CORINFO_INTRINSIC_Floor:
retNode = impMathIntrinsic(method, sig, callType, intrinsicID, tailCall);
// Can be optimized during morph
isSpecial = intrinsicID == CORINFO_INTRINSIC_Pow;
break;

#if defined(_TARGET_XARCH_) || defined(_TARGET_ARM64_)
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47 changes: 47 additions & 0 deletions src/jit/morph.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -8698,6 +8698,53 @@ GenTree* Compiler::fgMorphCall(GenTreeCall* call)
}
}

// Optimize Math.Pow(x, c)
if ((call->gtCallMoreFlags & GTF_CALL_M_SPECIAL_INTRINSIC) &&
info.compCompHnd->getIntrinsicID(call->gtCallMethHnd) == CORINFO_INTRINSIC_Pow)
{
noway_assert(call->fgArgInfo->ArgCount() == 2);
GenTree* arg0 = gtArgEntryByArgNum(call, 0)->node;
GenTree* arg1 = gtArgEntryByArgNum(call, 1)->node;
GenTree* newNode = nullptr;

if (arg1->IsCnsFltOrDbl())
{
noway_assert(arg0->TypeGet() == arg1->TypeGet());
GenTreeDblCon* powerCon = arg1->AsDblCon();

if (powerCon->gtDconVal == 2.0)
{
if (arg0->OperIs(GT_LCL_VAR))
{
// Math.Pow(x, 2) -> x*x where x is a local variable
newNode = gtNewOperNode(GT_MUL, powerCon->TypeGet(), arg0, gtCloneExpr(arg0));
}
else if (arg0->OperIs(GT_IND) && arg0->AsIndir()->Addr()->gtGetOp1()->OperIs(GT_LCL_VAR))
{
// Math.Pow(x, 2) -> x*x where x is a field
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The way the code is written the only field that it will recognize is the first field of a struct (the field at offset 0). I doubt that was the intention.

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@mikedn heh, definitely not the intention, I wish I actually could try the "introduce a tmp local" scenario instead.

newNode = gtNewOperNode(GT_MUL, powerCon->TypeGet(), arg0, gtCloneExpr(arg0));
}
}
else if (powerCon->gtDconVal == 1.0)
{
// Math.Pow(x, 1) -> x
newNode = arg0;
}
else if (powerCon->gtDconVal == -1.0)
{
// Math.Pow(x, -1) -> 1/x
newNode = gtNewOperNode(GT_DIV, powerCon->TypeGet(), gtNewDconNode(1, powerCon->TypeGet()), arg0);
}

if (newNode != nullptr)
{
INDEBUG(newNode->gtDebugFlags |= GTF_DEBUG_NODE_MORPHED);
DEBUG_DESTROY_NODE(call);
return newNode;
}
}
}

// Optimize get_ManagedThreadId(get_CurrentThread)
if ((call->gtCallMoreFlags & GTF_CALL_M_SPECIAL_INTRINSIC) &&
info.compCompHnd->getIntrinsicID(call->gtCallMethHnd) == CORINFO_INTRINSIC_GetManagedThreadId)
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