Represent managed-return-values as native vars

[jakobbotsch]

Update representation of managed return values to follow #128397.

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[Copilot]

Pull request overview

This PR updates CoreCLR JIT/VM debug-info plumbing to represent managed call return values as explicit ICorDebugInfo::NativeVarInfo entries (via a new CALL_RETURN_ILNUM sentinel plus a callReturnValueILOffset field), instead of relying on CALL_INSTRUCTION IP mapping entries. It also updates the compression/writer paths to encode this new data.

Changes:

• Extended NativeVarInfo (and the shared JIT interface model) with callReturnValueILOffset, and added CALL_RETURN_ILNUM / updated MAX_ILNUM.
• Updated debug info encoding/compression to treat CALL_RETURN_ILNUM specially (encode call IL offset; implicit native end offset).
• Updated the JIT to collect per-call return-value location info and removed call-site CALL_INSTRUCTION mapping emission in multiple emitters.

Reviewed changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/coreclr/vm/debuginfostore.cpp	Adds special-case encoding/decoding for CALL_RETURN_ILNUM and implicit fields.
src/coreclr/tools/Common/JitInterface/CorInfoTypes.VarInfo.cs	Extends NativeVarInfo model with callReturnValueILOffset.
src/coreclr/tools/Common/JitInterface/CorInfoTypes.cs	Adds CALL_RETURN_ILNUM and updates MAX_ILNUM.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/DebugInfoTableNode.cs	Updates R2R var blob writer to encode call-return entries differently.
src/coreclr/jit/scopeinfo.cpp	Adds emission of call-return var entries; updates getSiVarLoc signature/use.
src/coreclr/jit/emitxarch.cpp	Removes call-site mapping emission previously used for return value reporting.
src/coreclr/jit/emitwasm.cpp	Removes call-site mapping emission previously used for return value reporting.
src/coreclr/jit/emitriscv64.cpp	Removes call-site mapping emission previously used for return value reporting.
src/coreclr/jit/emitloongarch64.cpp	Removes call-site mapping emission previously used for return value reporting.
src/coreclr/jit/emitarm64.cpp	Removes call-site mapping emission previously used for return value reporting.
src/coreclr/jit/emitarm.cpp	Removes call-site mapping emission previously used for return value reporting.
src/coreclr/jit/emit.h	Replaces EmitCallParams.debugInfo with returnValueCall.
src/coreclr/jit/ee_il_dll.cpp	Updates var reporting storage to carry call IL offset; improves display of call-return entries.
src/coreclr/jit/compiler.h	Extends VarResultInfo and updates eeSetLVinfo signature for call return metadata.
src/coreclr/jit/codegenxarch.cpp	Switches call emission plumbing to pass returnValueCall.
src/coreclr/jit/codegenwasm.cpp	Switches call emission plumbing to pass returnValueCall.
src/coreclr/jit/codegenlinear.cpp	Initializes storage for emitted call-return info.
src/coreclr/jit/codegeninterface.h	Adds EmittedCallReturnInfo container and updates getSiVarLoc signature.
src/coreclr/jit/codegencommon.cpp	Captures return-value location after emitting a call and records it for scope info.
src/coreclr/jit/codegenarmarch.cpp	Switches call emission plumbing to pass returnValueCall.
src/coreclr/inc/cordebuginfo.h	Adds CALL_RETURN_ILNUM and extends NativeVarInfo with callReturnValueILOffset.

Comments suppressed due to low confidence (2)

src/coreclr/jit/scopeinfo.cpp:516

• getSiVarLoc now takes unsigned offset and then adds varDsc->GetStackOffset() (a signed stack offset that can be negative). This can underflow/wrap for typical frame-pointer locals (negative offsets), and then gets converted to int when constructing siVarLoc, producing incorrect stack locations in debug info.

CodeGenInterface::siVarLoc CodeGenInterface::getSiVarLoc(const LclVarDsc* varDsc, unsigned offset, unsigned stackLevel) const
{
// For stack vars, find the base register, and offset
regNumber baseReg;
offset += varDsc->GetStackOffset();
if (!varDsc->lvFramePointerBased)
{
baseReg = REG_SPBASE;
offset += stackLevel;
}
else
{
baseReg = REG_FPBASE;
}
return CodeGenInterface::siVarLoc(varDsc, baseReg, offset, isFramePointerUsed());
}

src/coreclr/jit/emit.h:496

• EmitCallParams removed the debugInfo field, but there are still target-specific codegen paths assigning params.debugInfo (e.g., in codegenloongarch64.cpp and codegenriscv64.cpp). This will break builds for those targets unless they are updated to the new returnValueCall mechanism.

struct EmitCallParams
{
EmitCallType callType = EC_COUNT;
CORINFO_METHOD_HANDLE methHnd = NO_METHOD_HANDLE;
#ifdef DEBUG
// Used to report call sites to the EE
CORINFO_SIG_INFO* sigInfo = nullptr;
#endif
void* addr = nullptr;
ssize_t argSize = 0;
emitAttr retSize = EA_PTRSIZE;
// For multi-reg args with GC returns in the second arg
emitAttr secondRetSize = EA_UNKNOWN;
bool hasAsyncRet = false;
BitVec ptrVars = BitVecOps::UninitVal();
regMaskTP gcrefRegs = RBM_NONE;
regMaskTP byrefRegs = RBM_NONE;
regNumber ireg = REG_NA;
regNumber xreg = REG_NA;
unsigned xmul = 0;
ssize_t disp = 0;
bool isJump = false;
bool noSafePoint = false;
// If this call should have managed return value debug info associated with it, this is the call to associate it with.
GenTreeCall* returnValueCall = nullptr;
#ifdef TARGET_WASM
CORINFO_WASM_TYPE_SYMBOL_HANDLE wasmSignature = nullptr;
#endif
};

[noahfalk]

Thanks @jakobbotsch! I don't have the background knowledge to usefully review the JIT code but overall this looked like what I was hoping for. Since the debug info reader and ICorDebug code will need to stay synced with the writer let me see if I can get someone on my team to handle the remainder so we could put the whole thing in as one atomic commit.

[tommcdon]

I believe MRV is only used in live debugging scenarios, which requires consuming these changes in the DBI. I think we could consume the change in CordbNativeCode::GetReturnValueLiveOffsetImpl, and then we can delete CordbNativeCode::GetCallInstructionLength as it would be dead code. Should we do the DBI change as well (I think it is relatively small, noting that we would be deleting a long, unused function as part of it :) ).

[Copilot]

Pull request overview

Copilot reviewed 32 out of 32 changed files in this pull request and generated 6 comments.

Comments suppressed due to low confidence (1)

src/coreclr/jit/emit.h:496

• EmitCallParams dropped the DebugInfo debugInfo field, but there are still backend codegen paths assigning to params.debugInfo (e.g., codegenriscv64.cpp / codegenloongarch64.cpp). As-is this will fail to compile for those targets; they likely need to be updated to use returnValueCall (or to stop emitting managed return value info on those backends).

struct EmitCallParams
{
EmitCallType callType = EC_COUNT;
CORINFO_METHOD_HANDLE methHnd = NO_METHOD_HANDLE;
#ifdef DEBUG
// Used to report call sites to the EE
CORINFO_SIG_INFO* sigInfo = nullptr;
#endif
void* addr = nullptr;
ssize_t argSize = 0;
emitAttr retSize = EA_PTRSIZE;
// For multi-reg args with GC returns in the second arg
emitAttr secondRetSize = EA_UNKNOWN;
bool hasAsyncRet = false;
BitVec ptrVars = BitVecOps::UninitVal();
regMaskTP gcrefRegs = RBM_NONE;
regMaskTP byrefRegs = RBM_NONE;
regNumber ireg = REG_NA;
regNumber xreg = REG_NA;
unsigned xmul = 0;
ssize_t disp = 0;
bool isJump = false;
bool noSafePoint = false;
// If this call should have managed return value debug info associated with it, this is the call to associate it with.
GenTreeCall* returnValueCall = nullptr;
#ifdef TARGET_WASM
CORINFO_WASM_TYPE_SYMBOL_HANDLE wasmSignature = nullptr;
#endif
};

[jakobbotsch]

Added the debugger and cDAC support :)

Thanks for doing that! I thought this would need change to the interface.

[Copilot]

Pull request overview

Copilot reviewed 38 out of 38 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 38 out of 38 changed files in this pull request and generated 3 comments.