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JIT: stop treating ManagedThreadId helper as constant/pure #130006

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JIT: stop treating ManagedThreadId helper as constant/pure #130006

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7bc14a5
Initial plan
Copilot Jun 29, 2026
faf6f9c
Remove ManagedThreadId value-numbering func mapping
Copilot Jun 29, 2026
83ba1f9
Handle surviving ManagedThreadId helper as opaque in VN
Copilot Jun 29, 2026
da58ef9
JIT: mark ManagedThreadId helper non-pure in helper properties
Copilot Jun 30, 2026
96f2825
Potential fix for pull request finding
VSadov Jun 30, 2026
3d1ab57
Add rationale comment for ManagedThreadId helper purity
Copilot Jun 30, 2026
0ca64b3
Fix JIT format issue and document thread ID helper behavior
Copilot Jun 30, 2026
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1 change: 0 additions & 1 deletion src/coreclr/jit/utils.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1560,7 +1560,6 @@ void HelperCallProperties::init()
break;

case CORINFO_HELP_GETCURRENTMANAGEDTHREADID:
isPure = true;
exceptions = ExceptionSetFlags::None;
break;
Comment on lines 1562 to 1566

@VSadov VSadov Jun 30, 2026

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@copilot add a comment mentioning that in runtime async methods managed thread ID is not a constant/pure value.
Also check the jit format failures.

Copilot AI Jun 30, 2026

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Addressed in 3d1ab57: added a rationale comment in HelperCallProperties::init() that in runtime async methods managed thread ID is not a constant/pure value, while the helper remains no-throw.

I also checked the jit format failure path: local jitformat.py couldn’t download clang-format in this environment, but I verified src/coreclr/jit/utils.cpp is clean with local clang-format -style=file (no diff).


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10 changes: 5 additions & 5 deletions src/coreclr/jit/valuenum.cpp
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Expand Up @@ -14946,11 +14946,6 @@ VNFunc Compiler::fgValueNumberJitHelperMethodVNFunc(CorInfoHelpFunc helpFunc)
vnf = VNF_Unbox_TypeTest;
break;

// A constant within any method.
case CORINFO_HELP_GETCURRENTMANAGEDTHREADID:
vnf = VNF_ManagedThreadId;
break;

case CORINFO_HELP_GETREFANY:
// TODO-CQ: This should really be interpreted as just a struct field reference, in terms of values.
vnf = VNF_GetRefanyVal;
Expand Down Expand Up @@ -15045,6 +15040,11 @@ bool Compiler::fgValueNumberHelperCall(GenTreeCall* call)
bool mayRunCctor = s_helperCallProperties.MayRunCctor(helpFunc);
bool noThrow = s_helperCallProperties.NoThrow(helpFunc);

if (helpFunc == CORINFO_HELP_GETCURRENTMANAGEDTHREADID)
{
pure = false;
}
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ValueNumPair vnpExc = ValueNumStore::VNPForEmptyExcSet();

// If the JIT helper can throw an exception make sure that we fill in
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2 changes: 0 additions & 2 deletions src/coreclr/jit/valuenumfuncs.h
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Expand Up @@ -114,8 +114,6 @@ ValueNumFuncDef(LeadingZeroCount, 1, false, false)
ValueNumFuncDef(TrailingZeroCount, 1, false, false)
ValueNumFuncDef(PopCount, 1, false, false)

ValueNumFuncDef(ManagedThreadId, 0, false, false)

ValueNumFuncDef(ObjGetType, 1, false, true)
ValueNumFuncDef(GetGcstaticBase, 1, false, true)
ValueNumFuncDef(GetNongcstaticBase, 1, false, true)
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