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Intrinsify Span.Slice(int,int) for Span[X..] #122065

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Intrinsify Span.Slice(int,int) for Span[X..] #122065

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Intrinsify Span.Slice(int,int) for Span[X..]
EgorBo Dec 1, 2025
4343cf2
minimize diffs
EgorBo Dec 1, 2025
f845d70
clean up
EgorBo Dec 1, 2025
990af0b
clean up
EgorBo Dec 1, 2025
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4 changes: 4 additions & 0 deletions src/coreclr/jit/fgbasic.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1570,6 +1570,10 @@ void Compiler::fgFindJumpTargets(const BYTE* codeAddr, IL_OFFSET codeSize, Fixed
compInlineResult->Note(InlineObservation::CALLSITE_FOLDABLE_INTRINSIC);
handled = true;
}
else if (ni == NI_System_Span_Slice || ni == NI_System_ReadOnlySpan_Slice)
{
// CI test, ignore diffs from these marked as intrinsics
}
else if (ni != NI_Illegal)
{
// Otherwise note "intrinsic" (most likely will be lowered as single instructions)
Expand Down
127 changes: 127 additions & 0 deletions src/coreclr/jit/importercalls.cpp
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Expand Up @@ -3744,6 +3744,125 @@ GenTree* Compiler::impIntrinsic(CORINFO_CLASS_HANDLE clsHnd,
break;
}

case NI_System_Span_Slice:
case NI_System_ReadOnlySpan_Slice:
{
assert(sig->sigInst.classInstCount == 1);
assert(sig->numArgs == 2);

if (compCurBB->isRunRarely())
{
return nullptr;
}

GenTree* lenArg = impStackTop(0).val;
GenTree* startArg = impStackTop(1).val;
GenTree* spanArg = impStackTop(2).val;

// When we have span.Slice(X, span.Length - X), we can optimize this to just span.Slice(X).
// Example arguments:
//
// spanArg:
// * LCL_VAR byref V01 loc0
//
// startArg:
// * CNS_INT int 8
//
// lenArg:
// * SUB int
// |-- * IND int
// | |-- * FIELD_ADDR byref System.Span`1[int]:_length
// | |-- * LCL_VAR byref V01 loc0
// |-- * CNS_INT int 8
//
if (lenArg->OperIs(GT_SUB) && ((startArg->gtFlags & GTF_ALL_EFFECT) == 0) &&
((spanArg->gtFlags & GTF_ALL_EFFECT) == 0))
{
GenTree* subOp1 = lenArg->gtGetOp1();
GenTree* subOp2 = lenArg->gtGetOp2();

if (GenTree::Compare(subOp2, startArg) && subOp1->OperIs(GT_IND) && subOp1->TypeIs(TYP_INT) &&
subOp1->gtGetOp1()->OperIs(GT_FIELD_ADDR) &&
GenTree::Compare(subOp1->gtGetOp1()->gtGetOp1(), spanArg))
{
CORINFO_FIELD_HANDLE refHnd = info.compCompHnd->getFieldInClass(clsHnd, 0);
CORINFO_FIELD_HANDLE lengthHnd = info.compCompHnd->getFieldInClass(clsHnd, 1);
unsigned refOffset = OFFSETOF__CORINFO_Span__reference;
unsigned lengthOffset = OFFSETOF__CORINFO_Span__length;

// It's unlikely to be anything other than the _length field, but just to be sure.
if (subOp1->gtGetOp1()->AsFieldAddr()->gtFldHnd != lengthHnd)
{
return nullptr;
}

// Clone spanArg for multiple uses:
GenTree* spanArgClone = nullptr;
if (impIsAddressInLocal(spanArg))
{
spanArgClone = gtCloneExpr(spanArg);
}
else
{
spanArg = impCloneExpr(spanArg, &spanArgClone, CHECK_SPILL_ALL,
nullptr DEBUGARG("Span.Slice spanArg"));
}

GenTreeFieldAddr* refFieldAddr = gtNewFieldAddrNode(refHnd, spanArg, refOffset);
GenTreeFieldAddr* lengthFieldAddr = gtNewFieldAddrNode(lengthHnd, spanArgClone, lengthOffset);

GenTree* oldRef = gtNewIndir(TYP_BYREF, refFieldAddr);
GenTree* oldLength = gtNewIndir(TYP_INT, lengthFieldAddr);
lengthFieldAddr->SetIsSpanLength(true);

CORINFO_CLASS_HANDLE spanHnd = sig->retTypeClass;
unsigned spanTempNum = lvaGrabTemp(true DEBUGARG("(ReadOnly)Span<T> for Slice"));
lvaSetStruct(spanTempNum, spanHnd, false);

// Emit the bounds check:
//
// if ((uint)start > (uint)oldLength)
// ThrowHelper.ThrowArgumentOutOfRangeException();
//
GenTree* oobCheck = gtNewOperNode(GT_LE, TYP_INT, startArg, oldLength);
oobCheck->SetUnsigned();
GenTreeCall* throwAOORE =
gtNewHelperCallNode(CORINFO_HELP_THROW_ARGUMENTOUTOFRANGEEXCEPTION, TYP_VOID);
GenTreeColon* oobCheckColon = gtNewColonNode(TYP_VOID, gtNewNothingNode(), throwAOORE);
GenTreeQmark* oobCheckQmark = gtNewQmarkNode(TYP_VOID, oobCheck, oobCheckColon);
impAppendTree(oobCheckQmark, CHECK_SPILL_ALL, impCurStmtDI);

// Create the new Span:
//
// _reference = oldRef + (nint)(start * sizeof(T))
// _length = oldLength - start
//
CORINFO_CLASS_HANDLE spanElemHnd = sig->sigInst.classInst[0];
const unsigned elemSize = info.compCompHnd->getClassSize(spanElemHnd);
assert(elemSize > 0);

// _reference:
GenTree* bytesOffset = gtFoldExpr(
gtNewOperNode(GT_MUL, TYP_INT, gtCloneExpr(startArg), gtNewIconNode(elemSize, TYP_INT)));
GenTree* bytesOffsetI = gtFoldExpr(impImplicitIorI4Cast(bytesOffset, TYP_I_IMPL));
GenTree* newRef = gtNewOperNode(GT_ADD, TYP_BYREF, oldRef, bytesOffsetI);
GenTree* refFieldStore = gtNewStoreLclFldNode(spanTempNum, TYP_BYREF, refOffset, newRef);

// _length:
GenTree* lenSubStart =
gtNewOperNode(GT_SUB, TYP_INT, gtCloneExpr(oldLength), gtCloneExpr(startArg));
GenTree* lengthFieldStore =
gtNewStoreLclFldNode(spanTempNum, TYP_INT, lengthOffset, gtFoldExpr(lenSubStart));

impPopStack(3);
impAppendTree(refFieldStore, CHECK_SPILL_ALL, impCurStmtDI);
impAppendTree(lengthFieldStore, CHECK_SPILL_ALL, impCurStmtDI);
return impCreateLocalNode(spanTempNum DEBUGARG(0));
}
}
break;
}

case NI_System_Span_get_Item:
case NI_System_ReadOnlySpan_get_Item:
{
Expand Down Expand Up @@ -10429,6 +10548,10 @@ NamedIntrinsic Compiler::lookupNamedIntrinsic(CORINFO_METHOD_HANDLE method)
{
result = NI_System_ReadOnlySpan_get_Length;
}
else if (strcmp(methodName, "Slice") == 0)
{
result = NI_System_ReadOnlySpan_Slice;
}
}
else if (strcmp(className, "RuntimeType") == 0)
{
Expand Down Expand Up @@ -10467,6 +10590,10 @@ NamedIntrinsic Compiler::lookupNamedIntrinsic(CORINFO_METHOD_HANDLE method)
{
result = NI_System_Span_get_Length;
}
else if (strcmp(methodName, "Slice") == 0)
{
result = NI_System_Span_Slice;
}
}
else if (strcmp(className, "SpanHelpers") == 0)
{
Expand Down
2 changes: 2 additions & 0 deletions src/coreclr/jit/namedintrinsiclist.h
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Expand Up @@ -141,11 +141,13 @@ enum NamedIntrinsic : unsigned short
NI_System_String_EndsWith,
NI_System_Span_get_Item,
NI_System_Span_get_Length,
NI_System_Span_Slice,
NI_System_SpanHelpers_ClearWithoutReferences,
NI_System_SpanHelpers_Fill,
NI_System_SpanHelpers_SequenceEqual,
NI_System_ReadOnlySpan_get_Item,
NI_System_ReadOnlySpan_get_Length,
NI_System_ReadOnlySpan_Slice,

NI_System_MemoryExtensions_AsSpan,
NI_System_MemoryExtensions_Equals,
Expand Down
1 change: 1 addition & 0 deletions src/libraries/System.Private.CoreLib/src/System/ReadOnlySpan.cs
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Expand Up @@ -384,6 +384,7 @@ public ReadOnlySpan<T> Slice(int start)
/// <exception cref="ArgumentOutOfRangeException">
/// Thrown when the specified <paramref name="start"/> or end index is not in range (&lt;0 or &gt;Length).
/// </exception>
[Intrinsic]
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public ReadOnlySpan<T> Slice(int start, int length)
{
Expand Down
1 change: 1 addition & 0 deletions src/libraries/System.Private.CoreLib/src/System/Span.cs
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Expand Up @@ -408,6 +408,7 @@ public Span<T> Slice(int start)
/// <exception cref="ArgumentOutOfRangeException">
/// Thrown when the specified <paramref name="start"/> or end index is not in range (&lt;0 or &gt;Length).
/// </exception>
[Intrinsic]
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public Span<T> Slice(int start, int length)
{
Expand Down
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