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Tune floating-point CSEs live across a call better #63903

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Jan 24, 2022
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Tune floating-point CSEs live across a call better #63903

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15 changes: 8 additions & 7 deletions src/coreclr/jit/optcse.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2598,17 +2598,18 @@ class CSE_Heuristic
cse_use_cost *= slotCount;
}

// If this CSE is live across a call then we may need to spill an additional caller save register
// If this CSE is live across a call then we may have additional costs
//
if (candidate->LiveAcrossCall())
{
if (candidate->Expr()->IsCnsFltOrDbl() && (CNT_CALLEE_SAVED_FLOAT == 0) &&
(candidate->CseDsc()->csdUseWtCnt <= 4))
// If we have a floating-point CSE that is both live across a call and there
// are no callee-saved FP registers available, the RA will have to spill at
// the def site and reload at the (first) use site, if the variable is a register
// candidate. Account for that.
if (varTypeIsFloating(candidate->Expr()) && (CNT_CALLEE_SAVED_FLOAT == 0) && !candidate->IsConservative())
{
// Floating point constants are expected to be contained, so unless there are more than 4 uses
// we better not to CSE them, especially on platforms without callee-saved registers
// for values living across calls
return false;
cse_def_cost += 1;
cse_use_cost += 1;
}

// If we don't have a lot of variables to enregister or we have a floating point type
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