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JIT: Use precise multireg arg check for old promotion #112883

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Merged
merged 2 commits into from
Feb 25, 2025
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JIT: Use precise multireg arg check for old promotion #112883

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JIT: Use precise multireg arg check for old promotion
jakobbotsch Feb 24, 2025
64d9fed
Quirk linux diffs
jakobbotsch Feb 25, 2025
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1 change: 1 addition & 0 deletions src/coreclr/jit/compiler.h
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Original file line number Diff line number Diff line change
Expand Up @@ -4435,6 +4435,7 @@ class Compiler
void PromoteStructVar(unsigned lclNum);
void SortStructFields();
bool IsArmHfaParameter(unsigned lclNum);
bool IsSysVMultiRegType(ClassLayout* layout);

var_types TryPromoteValueClassAsPrimitive(CORINFO_TYPE_LAYOUT_NODE* treeNodes, size_t maxTreeNodes, size_t index);
void AdvanceSubTree(CORINFO_TYPE_LAYOUT_NODE* treeNodes, size_t maxTreeNodes, size_t* index);
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28 changes: 26 additions & 2 deletions src/coreclr/jit/lclvars.cpp
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Expand Up @@ -2634,6 +2634,28 @@ bool Compiler::StructPromotionHelper::IsArmHfaParameter(unsigned lclNum)
return hfaType != CORINFO_HFA_ELEM_NONE;
}

//--------------------------------------------------------------------------------------------
// IsSysVMultiRegType - Check if a type is one that could be passed in 2
// registers in some cases.
// This is a quirk to match old promotion behavior.
//
// Arguments:
// lclNum - The local
//
// Return value:
// True if it sometimes may be passed in two registers.
//
bool Compiler::StructPromotionHelper::IsSysVMultiRegType(ClassLayout* layout)
{
#ifdef UNIX_AMD64_ABI
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not the case for arm64 (sysv/win)?

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Not according to diffs... To be honest I did not spend too much time looking at why this turns out to be a good heuristic for SysV, since I hope to remove all of this in this or next release.

SYSTEMV_AMD64_CORINFO_STRUCT_REG_PASSING_DESCRIPTOR structDesc;
compiler->eeGetSystemVAmd64PassStructInRegisterDescriptor(layout->GetClassHandle(), &structDesc);
return structDesc.passedInRegisters && (structDesc.eightByteCount == 2);
#else
return false;
#endif
}

//--------------------------------------------------------------------------------------------
// ShouldPromoteStructVar - Should a struct var be promoted if it can be promoted?
// This routine mainly performs profitability checks. Right now it also has
Expand Down Expand Up @@ -2693,10 +2715,10 @@ bool Compiler::StructPromotionHelper::ShouldPromoteStructVar(unsigned lclNum)
#if FEATURE_MULTIREG_STRUCT_PROMOTE
// Is this a variable holding a value with exactly two fields passed in
// multiple registers?
if (compiler->lvaIsMultiregStruct(varDsc, compiler->info.compIsVarArgs))
if (varDsc->lvIsMultiRegArg || IsSysVMultiRegType(varDsc->GetLayout()))
{
if ((structPromotionInfo.fieldCnt != 2) &&
!((structPromotionInfo.fieldCnt == 1) && varTypeIsSIMD(structPromotionInfo.fields[0].fldType)))
((structPromotionInfo.fieldCnt != 1) || !varTypeIsSIMD(structPromotionInfo.fields[0].fldType)))
{
JITDUMP("Not promoting multireg struct local V%02u, because lvIsParam is true, #fields != 2 and it's "
"not a single SIMD.\n",
Expand All @@ -2713,6 +2735,7 @@ bool Compiler::StructPromotionHelper::ShouldPromoteStructVar(unsigned lclNum)
}
else
#endif // !FEATURE_MULTIREG_STRUCT_PROMOTE
{

// TODO-PERF - Implement struct promotion for incoming single-register structs.
// Also the implementation of jmp uses the 4 byte move to store
Expand All @@ -2726,6 +2749,7 @@ bool Compiler::StructPromotionHelper::ShouldPromoteStructVar(unsigned lclNum)
lclNum, structPromotionInfo.fieldCnt);
shouldPromote = false;
}
}
}
else if ((lclNum == compiler->genReturnLocal) && (structPromotionInfo.fieldCnt > 1))
{
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