Partial re-revert of dotnet#104336. Only JIT fixes are included.

src/coreclr/jit/codegencommon.cpp

@@ -1517,29 +1517,6 @@ void CodeGen::genExitCode(BasicBlock* block)
  if (compiler->getNeedsGSSecurityCookie())
  {
  genEmitGSCookieCheck(jmpEpilog);
-
- if (jmpEpilog)
- {
- // Dev10 642944 -
- // The GS cookie check created a temp label that has no live
- // incoming GC registers, we need to fix that
-
- unsigned varNum;
- LclVarDsc* varDsc;
-
- /* Figure out which register parameters hold pointers */
-
- for (varNum = 0, varDsc = compiler->lvaTable; varNum < compiler->lvaCount && varDsc->lvIsRegArg;
- varNum++, varDsc++)
- {
- noway_assert(varDsc->lvIsParam);
-
- gcInfo.gcMarkRegPtrVal(varDsc->GetArgReg(), varDsc->TypeGet());
- }
-
- GetEmitter()->emitThisGCrefRegs = GetEmitter()->emitInitGCrefRegs = gcInfo.gcRegGCrefSetCur;
- GetEmitter()->emitThisByrefRegs = GetEmitter()->emitInitByrefRegs = gcInfo.gcRegByrefSetCur;
- }
  }
 
  genReserveEpilog(block);

src/coreclr/jit/emit.cpp

@@ -10427,9 +10427,9 @@ regMaskTP emitter::emitGetGCRegsKilledByNoGCCall(CorInfoHelpFunc helper)
 // of the last instruction in the region makes GC safe again.
 // In particular - once the IP is on the first instruction, but not executed it yet,
 // it is still safe to do GC.
-// The only special case is when NoGC region is used for prologs/epilogs.
-// In such case the GC info could be incorrect until the prolog completes and epilogs
-// may have unwindability restrictions, so the first instruction cannot have GC.
+// The only special case is when NoGC region is used for prologs.
+// In such case the GC info could be incorrect until the prolog completes, so the first
+// instruction cannot have GC.
 
 void emitter::emitDisableGC()
 {

src/coreclr/jit/emitinl.h

@@ -594,8 +594,7 @@ bool emitter::emitGenNoGCLst(Callback& cb)
  emitter::instrDesc* id = emitFirstInstrDesc(ig->igData);
  assert(id != nullptr);
  assert(id->idCodeSize() > 0);
- if (!cb(ig->igFuncIdx, ig->igOffs, ig->igSize, id->idCodeSize(),
- ig->igFlags & (IGF_FUNCLET_PROLOG | IGF_FUNCLET_EPILOG | IGF_EPILOG)))
+ if (!cb(ig->igFuncIdx, ig->igOffs, ig->igSize, id->idCodeSize(), ig->igFlags & (IGF_FUNCLET_PROLOG)))
  {
  return false;
  }

src/coreclr/jit/gcencode.cpp

@@ -4027,8 +4027,7 @@ class InterruptibleRangeReporter
  // Report everything between the previous region and the current
  // region as interruptible.
 
- bool operator()(
- unsigned igFuncIdx, unsigned igOffs, unsigned igSize, unsigned firstInstrSize, bool isInPrologOrEpilog)
+ bool operator()(unsigned igFuncIdx, unsigned igOffs, unsigned igSize, unsigned firstInstrSize, bool isInProlog)
  {
  if (igOffs < m_uninterruptibleEnd)
  {
@@ -4042,9 +4041,9 @@ class InterruptibleRangeReporter
  if (igOffs > m_uninterruptibleEnd)
  {
  // Once the first instruction in IG executes, we cannot have GC.
- // But it is ok to have GC while the IP is on the first instruction, unless we are in prolog/epilog.
+ // But it is ok to have GC while the IP is on the first instruction, unless we are in prolog.
  unsigned interruptibleEnd = igOffs;
- if (!isInPrologOrEpilog)
+ if (!isInProlog)
  {
  interruptibleEnd += firstInstrSize;
  }

src/coreclr/nativeaot/Runtime/thread.cpp

@@ -675,10 +675,16 @@ void Thread::HijackCallback(NATIVE_CONTEXT* pThreadContext, void* pThreadToHijac
  if (runtime->IsConservativeStackReportingEnabled() ||
  codeManager->IsSafePoint(pvAddress))
  {
+ // IsUnwindable is precise on arm64, but can give false negatives on other architectures.
+ // (when IP is on the first instruction of an epilog, we still can unwind,
+ // but we can tell if the instruction is the first only if we can navigate instructions backwards and check)
+ // The preciseness of IsUnwindable is tracked in https://github.com/dotnet/runtime/issues/101932
+#if defined(TARGET_ARM64)
  // we may not be able to unwind in some locations, such as epilogs.
  // such locations should not contain safe points.
  // when scanning conservatively we do not need to unwind
  ASSERT(codeManager->IsUnwindable(pvAddress) || runtime->IsConservativeStackReportingEnabled());
+#endif
 
  // if we are not given a thread to hijack
  // perform in-line wait on the current thread