[WinEH] Make llvm.x86.seh.recoverfp work on x64

It adjusts from RSP-after-prologue to RBP, which is what SEH filters
need to do before they can use llvm.localrecover.

Fixes SEH filter captures, which were broken in r250088.

Issue reported by Alex Crichton.

llvm-svn: 255707

1 files changed, 11 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/WinException.cpp b/llvm/lib/CodeGen/AsmPrinter/WinException.cpp
index e2994172415..c4f650e89e0 100644
--- a/llvm/lib/CodeGen/AsmPrinter/WinException.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/WinException.cpp
@@ -506,8 +506,18 @@ InvokeStateChangeIterator &InvokeStateChangeIterator::scan() {
 void WinException::emitCSpecificHandlerTable(const MachineFunction *MF) {
   auto &OS = *Asm->OutStreamer;
   MCContext &Ctx = Asm->OutContext;
-
   const WinEHFuncInfo &FuncInfo = *MF->getWinEHFuncInfo();
+
+  // Emit a label assignment with the SEH frame offset so we can use it for
+  // llvm.x86.seh.recoverfp.
+  StringRef FLinkageName =
+      GlobalValue::getRealLinkageName(MF->getFunction()->getName());
+  MCSymbol *ParentFrameOffset =
+      Ctx.getOrCreateParentFrameOffsetSymbol(FLinkageName);
+  const MCExpr *MCOffset =
+      MCConstantExpr::create(FuncInfo.SEHSetFrameOffset, Ctx);
+  Asm->OutStreamer->EmitAssignment(ParentFrameOffset, MCOffset);
+
   // Use the assembler to compute the number of table entries through label
   // difference and division.
   MCSymbol *TableBegin =