[WinEH] Create an llvm.x86.seh.exceptioninfo intrinsic

This intrinsic is like framerecover plus a load. It recovers the EH
registration stack allocation from the parent frame and loads the
exception information field out of it, giving back a pointer to an
EXCEPTION_POINTERS struct. It's designed for clang to use in SEH filter
expressions instead of accessing the EXCEPTION_POINTERS parameter that
is available on x64.

This required a minor change to MC to allow defining a label variable to
another absolute framerecover label variable.

llvm-svn: 239567

1 files changed, 18 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/WinException.cpp b/llvm/lib/CodeGen/AsmPrinter/WinException.cpp
index 40d6bab8b6d..75287fd9855 100644
--- a/llvm/lib/CodeGen/AsmPrinter/WinException.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/WinException.cpp
@@ -449,7 +449,7 @@ void WinException::emitCXXFrameHandler3Table(const MachineFunction *MF) {
               Asm->OutContext.getOrCreateParentFrameOffsetSymbol(
                   GlobalValue::getRealLinkageName(HT.Handler->getName()));
           const MCSymbolRefExpr *ParentFrameOffsetRef = MCSymbolRefExpr::create(
-              ParentFrameOffset, MCSymbolRefExpr::VK_None, Asm->OutContext);
+              ParentFrameOffset, Asm->OutContext);
           OS.EmitValue(ParentFrameOffsetRef, 4); // ParentFrameOffset
         }
       }
@@ -551,11 +551,26 @@ void WinException::extendIP2StateTable(const MachineFunction *MF,
 /// functionally equivalent to the __C_specific_handler table, except it is
 /// indexed by state number instead of IP.
 void WinException::emitExceptHandlerTable(const MachineFunction *MF) {
-  auto &OS = *Asm->OutStreamer;
+  MCStreamer &OS = *Asm->OutStreamer;
 
-  // Emit the __ehtable label that we use for llvm.x86.seh.lsda.
+  // Define the EH registration node offset label in terms of its frameescape
+  // label. The WinEHStatePass ensures that the registration node is passed to
+  // frameescape. This allows SEH filter functions to access the
+  // EXCEPTION_POINTERS field, which is filled in by the _except_handlerN.
   const Function *F = MF->getFunction();
+  WinEHFuncInfo &FuncInfo = MMI->getWinEHFuncInfo(F);
+  assert(FuncInfo.EHRegNodeEscapeIndex != INT_MAX &&
+         "no EH reg node frameescape index");
   StringRef FLinkageName = GlobalValue::getRealLinkageName(F->getName());
+  MCSymbol *ParentFrameOffset =
+      Asm->OutContext.getOrCreateParentFrameOffsetSymbol(FLinkageName);
+  MCSymbol *FrameAllocSym = Asm->OutContext.getOrCreateFrameAllocSymbol(
+      FLinkageName, FuncInfo.EHRegNodeEscapeIndex);
+  const MCSymbolRefExpr *FrameAllocSymRef =
+      MCSymbolRefExpr::create(FrameAllocSym, Asm->OutContext);
+  OS.EmitAssignment(ParentFrameOffset, FrameAllocSymRef);
+
+  // Emit the __ehtable label that we use for llvm.x86.seh.lsda.
   MCSymbol *LSDALabel = Asm->OutContext.getOrCreateLSDASymbol(FLinkageName);
   OS.EmitLabel(LSDALabel);