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JIT: Expand optRelopImpliesRelop for constants as op1 #102024

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May 11, 2024
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JIT: Expand optRelopImpliesRelop for constants as op1 #102024

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a0b20ce
JIT: Expand optRelopImpliesRelop for constants as op1
jakobbotsch May 8, 2024
f07ccfe
Fix TP
jakobbotsch May 10, 2024
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3 changes: 3 additions & 0 deletions src/coreclr/jit/compiler.h
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Original file line number Diff line number Diff line change
Expand Up @@ -7501,6 +7501,9 @@ class Compiler
BitVecTraits* optReachableBitVecTraits;
BitVec optReachableBitVec;
void optRelopImpliesRelop(RelopImplicationInfo* rii);
bool optRelopTryInferWithOneEqualOperand(const VNFuncApp& domApp,
const VNFuncApp& treeApp,
RelopImplicationInfo* rii);

/**************************************************************************
* Value/Assertion propagation
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172 changes: 113 additions & 59 deletions src/coreclr/jit/redundantbranchopts.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -509,66 +509,11 @@ void Compiler::optRelopImpliesRelop(RelopImplicationInfo* rii)
}
}

// Given R(x, cns1) and R*(x, cns2) see if we can infer R* from R.
// We assume cns1 and cns2 are always on the RHS of the compare.
if ((treeApp.m_args[0] == domApp.m_args[0]) && vnStore->IsVNConstant(treeApp.m_args[1]) &&
vnStore->IsVNConstant(domApp.m_args[1]) && varTypeIsIntOrI(vnStore->TypeOfVN(treeApp.m_args[1])) &&
vnStore->TypeOfVN(domApp.m_args[0]) == vnStore->TypeOfVN(treeApp.m_args[1]) &&
vnStore->TypeOfVN(domApp.m_args[1]) == vnStore->TypeOfVN(treeApp.m_args[1]))
if (((treeApp.m_args[0] == domApp.m_args[0]) || (treeApp.m_args[0] == domApp.m_args[1]) ||
(treeApp.m_args[1] == domApp.m_args[0]) || (treeApp.m_args[1] == domApp.m_args[1])) &&
optRelopTryInferWithOneEqualOperand(domApp, treeApp, rii))
{
// We currently don't handle VNF_relop_UN funcs here
if (ValueNumStore::VNFuncIsSignedComparison(domApp.m_func) &&
ValueNumStore::VNFuncIsSignedComparison(treeApp.m_func))
{
// Dominating "X relop CNS"
const genTreeOps domOper = static_cast<genTreeOps>(domApp.m_func);
const target_ssize_t domCns = vnStore->CoercedConstantValue<target_ssize_t>(domApp.m_args[1]);

// Dominated "X relop CNS"
const genTreeOps treeOper = static_cast<genTreeOps>(treeApp.m_func);
const target_ssize_t treeCns = vnStore->CoercedConstantValue<target_ssize_t>(treeApp.m_args[1]);

// Example:
//
// void Test(int x)
// {
// if (x > 100)
// if (x > 10)
// Console.WriteLine("Taken!");
// }
//

// Corresponding BB layout:
//
// BB1:
// if (x <= 100)
// goto BB4
//
// BB2:
// // x is known to be > 100 here
// if (x <= 10) // never true
// goto BB4
//
// BB3:
// Console.WriteLine("Taken!");
//
// BB4:
// return;

// Check whether the dominating compare being "false" implies the dominated compare is known
// to be either "true" or "false".
RelopResult treeOperStatus =
IsCmp2ImpliedByCmp1(GenTree::ReverseRelop(domOper), domCns, treeOper, treeCns);
if (treeOperStatus != RelopResult::Unknown)
{
rii->canInfer = true;
rii->vnRelation = ValueNumStore::VN_RELATION_KIND::VRK_Inferred;
rii->canInferFromTrue = false;
rii->canInferFromFalse = true;
rii->reverseSense = treeOperStatus == RelopResult::AlwaysTrue;
return;
}
}
return;
}
}

Expand Down Expand Up @@ -646,6 +591,115 @@ void Compiler::optRelopImpliesRelop(RelopImplicationInfo* rii)
}
}

//------------------------------------------------------------------------
// optRelopTryInferWithOneEqualOperand: Given a domnating relop R(x, y) and
// another relop R*(a, b) that share an operand, try to see if we can infer
// something about R*(a, b).
//
// Arguments:
// domApp - The dominating relop R*(x, y)
// treeApp - The dominated relop R*(a, b)
// rii - [out] struct with relop implication information
//
// Returns:
// True if something was inferred; otherwise false.
//
bool Compiler::optRelopTryInferWithOneEqualOperand(const VNFuncApp& domApp,
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If not being handled in this PR, could you log an issue for enabling the same to be done for TYP_SIMD?

We have all the same relops and same transforms that are valid there as well, so it'd be nice to ensure consistency

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I'm not really sure what that would entail. We already give up on relops between floating points because many of these inferences don't hold there.
I think you should open an issue about the inferences you think we should be able to make for these.

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Commutative swapping should still apply. That is, x > y is the same as y < x even for floating-point.

What doesn't hold true is that x > y is not the same as !(x <= y) (but only due to NaN, so if we know the inputs aren't NaN it becomes safe)

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I'll work on getting an issue open for it

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This PR doesn't do the kind of general canonicalization of VNs we were discussing on Discord the other day. Since @SingleAccretion pointed out that this came with non-trivial TP considerations, I just decided to do the easy thing and canonicalize right at this point, which is part of RBO's reasoning about inequalities. This PR doesn't really change much except it allows some of that reasoning to apply for a few more cases.

const VNFuncApp& treeApp,
RelopImplicationInfo* rii)
{
// Canonicalize constants to be on the right.
VNFunc domFunc = domApp.m_func;
ValueNum domOp1 = domApp.m_args[0];
ValueNum domOp2 = domApp.m_args[1];

VNFunc treeFunc = treeApp.m_func;
ValueNum treeOp1 = treeApp.m_args[0];
ValueNum treeOp2 = treeApp.m_args[1];

if (vnStore->IsVNConstant(domOp1))
{
std::swap(domOp1, domOp2);
domFunc = ValueNumStore::SwapRelop(domFunc);
}

if (vnStore->IsVNConstant(treeOp1))
{
std::swap(treeOp1, treeOp2);
treeFunc = ValueNumStore::SwapRelop(treeFunc);
}

// Given R(x, cns1) and R*(x, cns2) see if we can infer R* from R.
if ((treeOp1 != domOp1) || !vnStore->IsVNConstant(treeOp2) || !vnStore->IsVNConstant(domOp2))
{
return false;
}

var_types treeOp1Type = vnStore->TypeOfVN(treeOp1);
var_types treeOp2Type = vnStore->TypeOfVN(treeOp2);
var_types domOp1Type = vnStore->TypeOfVN(domOp1);
var_types domOp2Type = vnStore->TypeOfVN(domOp2);
if (!varTypeIsIntOrI(treeOp1Type) || (domOp1Type != treeOp2Type) || (domOp2Type != treeOp2Type))
{
return false;
}
// We currently don't handle VNF_relop_UN funcs here
if (!ValueNumStore::VNFuncIsSignedComparison(domFunc) || !ValueNumStore::VNFuncIsSignedComparison(treeFunc))
{
return false;
}

// Dominating "X relop CNS"
const genTreeOps domOper = static_cast<genTreeOps>(domFunc);
const target_ssize_t domCns = vnStore->CoercedConstantValue<target_ssize_t>(domOp2);

// Dominated "X relop CNS"
const genTreeOps treeOper = static_cast<genTreeOps>(treeFunc);
const target_ssize_t treeCns = vnStore->CoercedConstantValue<target_ssize_t>(treeOp2);

// Example:
//
// void Test(int x)
// {
// if (x > 100)
// if (x > 10)
// Console.WriteLine("Taken!");
// }
//

// Corresponding BB layout:
//
// BB1:
// if (x <= 100)
// goto BB4
//
// BB2:
// // x is known to be > 100 here
// if (x <= 10) // never true
// goto BB4
//
// BB3:
// Console.WriteLine("Taken!");
//
// BB4:
// return;

// Check whether the dominating compare being "false" implies the dominated compare is known
// to be either "true" or "false".
RelopResult treeOperStatus = IsCmp2ImpliedByCmp1(GenTree::ReverseRelop(domOper), domCns, treeOper, treeCns);
if (treeOperStatus == RelopResult::Unknown)
{
return false;
}

rii->canInfer = true;
rii->vnRelation = ValueNumStore::VN_RELATION_KIND::VRK_Inferred;
rii->canInferFromTrue = false;
rii->canInferFromFalse = true;
rii->reverseSense = treeOperStatus == RelopResult::AlwaysTrue;
return true;
}

//------------------------------------------------------------------------
// optRedundantBranch: try and optimize a possibly redundant branch
//
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