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[clr-interp] Add safepoints at method entry and backwards branch #115567

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Merged
BrzVlad merged 2 commits into from
May 17, 2025
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[clr-interp] Add safepoints at method entry and backwards branch #115567

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[clr-interp] Add safepoints at method entry and backwards branch
BrzVlad May 14, 2025
9381226
[clr-interp] Add some starting contracts to interp exec method
BrzVlad May 14, 2025
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8 changes: 8 additions & 0 deletions src/coreclr/interpreter/compiler.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1418,6 +1418,10 @@ void InterpCompiler::EmitBranch(InterpOpcode opcode, int32_t ilOffset)
if (target < 0 || target >= m_ILCodeSize)
assert(0);

// Backwards branch, emit safepoint
if (ilOffset < 0)
AddIns(INTOP_SAFEPOINT);

InterpBasicBlock *pTargetBB = m_ppOffsetToBB[target];
assert(pTargetBB != NULL);

Expand Down Expand Up @@ -2113,6 +2117,10 @@ int InterpCompiler::GenerateCode(CORINFO_METHOD_INFO* methodInfo)

codeEnd = m_ip + m_ILCodeSize;

// Safepoint at each method entry. This could be done as part of a call, rather than
// adding an opcode.
AddIns(INTOP_SAFEPOINT);

@janvorli janvorli May 15, 2025

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Is there any reason to not to do it as part of the call that made you add the instruction instead?

@BrzVlad BrzVlad May 15, 2025

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Not a very serious reason. Felt cleaner to have a separate instruction for now, given calls in general are an area that will keep suffering modifications in the future.

@jkotas jkotas May 17, 2025

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Regular CoreCLR JIT expects the safe point to be at the callsite, not in the method entry.

This mismatch between the regular CoreCLR JIT suspension model and interpreter suspension model can lead to GC starvation (GC suspension taking a long time in corner cases). It may be better to inserts the safe point after the call to avoid these subtle issues.


linkBBlocks = true;
needsRetryEmit = false;
retry_emit:
Expand Down
1 change: 1 addition & 0 deletions src/coreclr/interpreter/intops.def
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Expand Up @@ -35,6 +35,7 @@ OPDEF(INTOP_LDLOCA, "ldloca", 3, 1, 0, InterpOpInt)

OPDEF(INTOP_SWITCH, "switch", 0, 0, 1, InterpOpSwitch)

OPDEF(INTOP_SAFEPOINT, "safepoint", 1, 0, 0, InterpOpNoArgs)
OPDEF(INTOP_BR, "br", 2, 0, 0, InterpOpBranch)

OPDEF(INTOP_BRFALSE_I4, "brfalse.i4", 3, 0, 1, InterpOpBranch)
Expand Down
13 changes: 13 additions & 0 deletions src/coreclr/vm/interpexec.cpp
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Expand Up @@ -35,6 +35,13 @@ static void InterpBreakpoint()

void InterpExecMethod(InterpreterFrame *pInterpreterFrame, InterpMethodContextFrame *pFrame, InterpThreadContext *pThreadContext)
{
CONTRACTL
{
GC_TRIGGERS;
MODE_COOPERATIVE;
}
CONTRACTL_END;

#if defined(HOST_AMD64) && defined(HOST_WINDOWS)
pInterpreterFrame->SetInterpExecMethodSSP((TADDR)_rdsspq());
#endif // HOST_AMD64 && HOST_WINDOWS
Expand Down Expand Up @@ -292,6 +299,12 @@ void InterpExecMethod(InterpreterFrame *pInterpreterFrame, InterpMethodContextFr
break;
}

case INTOP_SAFEPOINT:
if (g_TrapReturningThreads)
JIT_PollGC();
ip++;
break;

case INTOP_BR:
ip += ip[1];
break;
Expand Down