Do not report FP restores in x86 epilogs.

The x86 unwinder neither needs nor expects to see these restores (which
right now consist solely of a `vzeroupper` instruction that is emitted
to eliminate AVX <-> SSE transition penalties), which was causing unwind
failures under GC stress. This change stops reporting these restores as
part of a function epilog.

Fixes #9452.

1 files changed, 9 insertions, 4 deletions

diff --git a/src/jit/emit.h b/src/jit/emit.h
index f57cc0a0f7..186c60f4a8 100644
--- a/src/jit/emit.h
+++ b/src/jit/emit.h
@@ -1518,14 +1518,21 @@ protected:
     // IG of the epilog, and use it to find the epilog offset at the end of code generation.
     struct EpilogList
     {
-        EpilogList* elNext;
-        insGroup*   elIG;
+        EpilogList*  elNext;
+        emitLocation elLoc;
+
+        EpilogList()
+            : elNext(nullptr), elLoc()
+        {
+        }
     };
 
     EpilogList* emitEpilogList; // per method epilog list - head
     EpilogList* emitEpilogLast; // per method epilog list - tail
 
 public:
+    void emitStartEpilog();
+
     bool emitHasEpilogEnd();
 
     size_t emitGenEpilogLst(size_t (*fp)(void*, unsigned), void* cp);
@@ -1535,8 +1542,6 @@ public:
     void emitBegPrologEpilog(insGroup* igPh);
     void emitEndPrologEpilog();
 
-    emitLocation emitEpilogBegLoc;
-
     void emitBegFnEpilog(insGroup* igPh);
     void emitEndFnEpilog();