[WinEH] Fix ESP management with 32-bit __CxxFrameHandler3

The C++ EH personality automatically restores ESP from the C++ EH
registration node after a catchret. I mistakenly thought it was like
SEH, which does not restore ESP.

It makes sense for C++ EH to differ from SEH here because SEH does not
use funclets for catches, and does not allow catching inside of finally.
C++ EH may need to unwind through multiple catch funclets and eventually
catchret to some outer funclet. Therefore, the runtime has to keep track
of which ESP to use with catchret, rather than having the compiler
reload it manually.

llvm-svn: 253084

1 files changed, 13 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86FrameLowering.cpp b/llvm/lib/Target/X86/X86FrameLowering.cpp
index 302fc936744..394151b0b06 100644
--- a/llvm/lib/Target/X86/X86FrameLowering.cpp
+++ b/llvm/lib/Target/X86/X86FrameLowering.cpp
@@ -1246,6 +1246,19 @@ void X86FrameLowering::emitPrologue(MachineFunction &MF,
   } else if (IsFunclet && STI.is32Bit()) {
     // Reset EBP / ESI to something good for funclets.
     MBBI = restoreWin32EHStackPointers(MBB, MBBI, DL);
+    // If we're a catch funclet, we can be returned to via catchret. Save ESP
+    // into the registration node so that the runtime will restore it for us.
+    if (!MBB.isCleanupFuncletEntry()) {
+      assert(classifyEHPersonality(Fn->getPersonalityFn()) ==
+             EHPersonality::MSVC_CXX);
+      unsigned FrameReg;
+      int FI = MMI.getWinEHFuncInfo(Fn).EHRegNodeFrameIndex;
+      int64_t EHRegOffset = getFrameIndexReference(MF, FI, FrameReg);
+      // ESP is the first field, so no extra displacement is needed.
+      addRegOffset(BuildMI(MBB, MBBI, DL, TII.get(X86::MOV32mr)), FrameReg,
+                   false, EHRegOffset)
+          .addReg(X86::ESP);
+    }
   }
 
   while (MBBI != MBB.end() && MBBI->getFlag(MachineInstr::FrameSetup)) {