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JIT: Fix unnecessary GC transitions recorded for tailcalls #120934

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JIT: Fix unnecessary GC transitions recorded for tailcalls #120934

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Initial plan
Copilot Oct 21, 2025
347b910
Fix unnecessary GC transitions for tail calls in all JIT emitters
Copilot Oct 21, 2025
19623d2
Make fix more concise using ternary operator for savedSet
Copilot Oct 21, 2025
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17 changes: 14 additions & 3 deletions src/coreclr/jit/emitarm.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4678,9 +4678,20 @@ void emitter::emitIns_Call(const EmitCallParams& params)
assert((unsigned)abs(params.argSize) <= codeGen->genStackLevel);

// Trim out any callee-trashed registers from the live set.
regMaskTP savedSet = emitGetGCRegsSavedOrModified(params.methHnd);
regMaskTP gcrefRegs = params.gcrefRegs & savedSet;
regMaskTP byrefRegs = params.byrefRegs & savedSet;
// For tail calls, we don't trim registers since we're jumping to another function, not returning.
regMaskTP gcrefRegs;
regMaskTP byrefRegs;
if (params.isJump)
{
gcrefRegs = params.gcrefRegs;
byrefRegs = params.byrefRegs;
}
else
{
regMaskTP savedSet = emitGetGCRegsSavedOrModified(params.methHnd);
gcrefRegs = params.gcrefRegs & savedSet;
byrefRegs = params.byrefRegs & savedSet;
}

#ifdef DEBUG
if (EMIT_GC_VERBOSE)
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17 changes: 14 additions & 3 deletions src/coreclr/jit/emitarm64.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -9122,9 +9122,20 @@ void emitter::emitIns_Call(const EmitCallParams& params)
assert((unsigned)std::abs(params.argSize) <= codeGen->genStackLevel);

// Trim out any callee-trashed registers from the live set.
regMaskTP savedSet = emitGetGCRegsSavedOrModified(params.methHnd);
regMaskTP gcrefRegs = params.gcrefRegs & savedSet;
regMaskTP byrefRegs = params.byrefRegs & savedSet;
// For tail calls, we don't trim registers since we're jumping to another function, not returning.
regMaskTP gcrefRegs;
regMaskTP byrefRegs;
if (params.isJump)
{
gcrefRegs = params.gcrefRegs;
byrefRegs = params.byrefRegs;
}
else
{
regMaskTP savedSet = emitGetGCRegsSavedOrModified(params.methHnd);
gcrefRegs = params.gcrefRegs & savedSet;
byrefRegs = params.byrefRegs & savedSet;
}

#ifdef DEBUG
if (EMIT_GC_VERBOSE)
Expand Down
17 changes: 14 additions & 3 deletions src/coreclr/jit/emitloongarch64.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2394,9 +2394,20 @@ void emitter::emitIns_Call(const EmitCallParams& params)
assert((unsigned)std::abs(params.argSize) <= codeGen->genStackLevel);

// Trim out any callee-trashed registers from the live set.
regMaskTP savedSet = emitGetGCRegsSavedOrModified(params.methHnd);
regMaskTP gcrefRegs = params.gcrefRegs & savedSet;
regMaskTP byrefRegs = params.byrefRegs & savedSet;
// For tail calls, we don't trim registers since we're jumping to another function, not returning.
regMaskTP gcrefRegs;
regMaskTP byrefRegs;
if (params.isJump)
{
gcrefRegs = params.gcrefRegs;
byrefRegs = params.byrefRegs;
}
else
{
regMaskTP savedSet = emitGetGCRegsSavedOrModified(params.methHnd);
gcrefRegs = params.gcrefRegs & savedSet;
byrefRegs = params.byrefRegs & savedSet;
}
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@jakobbotsch jakobbotsch Oct 21, 2025

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@copilot This fix looks good, but can we make it a bit terser by using a ternary for savedSet and making it equal RBM_ALLINT in the params.isJump case?

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Copilot AI Oct 21, 2025

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Done in commit 9c6c876. Used ternary operator with RBM_ALLINT for tail calls across all 5 architecture emitters.


#ifdef DEBUG
if (EMIT_GC_VERBOSE)
Expand Down
17 changes: 14 additions & 3 deletions src/coreclr/jit/emitriscv64.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1792,9 +1792,20 @@ void emitter::emitIns_Call(const EmitCallParams& params)
assert((unsigned)std::abs(params.argSize) <= codeGen->genStackLevel);

// Trim out any callee-trashed registers from the live set.
regMaskTP savedSet = emitGetGCRegsSavedOrModified(params.methHnd);
regMaskTP gcrefRegs = params.gcrefRegs & savedSet;
regMaskTP byrefRegs = params.byrefRegs & savedSet;
// For tail calls, we don't trim registers since we're jumping to another function, not returning.
regMaskTP gcrefRegs;
regMaskTP byrefRegs;
if (params.isJump)
{
gcrefRegs = params.gcrefRegs;
byrefRegs = params.byrefRegs;
}
else
{
regMaskTP savedSet = emitGetGCRegsSavedOrModified(params.methHnd);
gcrefRegs = params.gcrefRegs & savedSet;
byrefRegs = params.byrefRegs & savedSet;
}

#ifdef DEBUG
if (EMIT_GC_VERBOSE)
Expand Down
17 changes: 14 additions & 3 deletions src/coreclr/jit/emitxarch.cpp
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -11172,9 +11172,20 @@ void emitter::emitIns_Call(const EmitCallParams& params)
assert((unsigned)abs((signed)params.argSize) <= codeGen->genStackLevel);

// Trim out any callee-trashed registers from the live set.
regMaskTP savedSet = emitGetGCRegsSavedOrModified(params.methHnd);
regMaskTP gcrefRegs = params.gcrefRegs & savedSet;
regMaskTP byrefRegs = params.byrefRegs & savedSet;
// For tail calls, we don't trim registers since we're jumping to another function, not returning.
regMaskTP gcrefRegs;
regMaskTP byrefRegs;
if (params.isJump)
{
gcrefRegs = params.gcrefRegs;
byrefRegs = params.byrefRegs;
}
else
{
regMaskTP savedSet = emitGetGCRegsSavedOrModified(params.methHnd);
gcrefRegs = params.gcrefRegs & savedSet;
byrefRegs = params.byrefRegs & savedSet;
}

#ifdef DEBUG
if (EMIT_GC_VERBOSE)
Expand Down
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