[llvm] Win x64 Unwind V2 1/n: Mark beginning and end of epilogs (#110024)

Windows x64 Unwind V2 adds epilog information to unwind data:
specifically, the length of the epilog and the offset of each epilog.

The first step to do this is to add markers to the beginning and end of
each epilog when generating Windows x64 code. I've modelled this after
how LLVM was marking ARM and AArch64 epilogs in Windows (and unified the
code between the three).

1 files changed, 30 insertions, 0 deletions

diff --git a/llvm/lib/MC/MCStreamer.cpp b/llvm/lib/MC/MCStreamer.cpp
index e690723..462ebfe 100644
--- a/llvm/lib/MC/MCStreamer.cpp
+++ b/llvm/lib/MC/MCStreamer.cpp
@@ -1013,6 +1013,36 @@ void MCStreamer::emitWinCFIEndProlog(SMLoc Loc) {
   CurFrame->PrologEnd = Label;
 }
 
+void MCStreamer::emitWinCFIBeginEpilogue(SMLoc Loc) {
+  WinEH::FrameInfo *CurFrame = EnsureValidWinFrameInfo(Loc);
+  if (!CurFrame)
+    return;
+
+  if (!CurFrame->PrologEnd)
+    return getContext().reportError(
+        Loc, "starting epilogue (.seh_startepilogue) before prologue has ended "
+             "(.seh_endprologue) in " +
+                 CurFrame->Function->getName());
+
+  InEpilogCFI = true;
+  CurrentEpilog = emitCFILabel();
+}
+
+void MCStreamer::emitWinCFIEndEpilogue(SMLoc Loc) {
+  WinEH::FrameInfo *CurFrame = EnsureValidWinFrameInfo(Loc);
+  if (!CurFrame)
+    return;
+
+  if (!InEpilogCFI)
+    return getContext().reportError(Loc, "Stray .seh_endepilogue in " +
+                                             CurFrame->Function->getName());
+
+  InEpilogCFI = false;
+  MCSymbol *Label = emitCFILabel();
+  CurFrame->EpilogMap[CurrentEpilog].End = Label;
+  CurrentEpilog = nullptr;
+}
+
 void MCStreamer::emitCOFFSafeSEH(MCSymbol const *Symbol) {}
 
 void MCStreamer::emitCOFFSymbolIndex(MCSymbol const *Symbol) {}