[llvm] [win][x64] Various fixes for unwind v2 (PR #154834)

[Eli Friedman via llvm-commits]

================
@@ -190,8 +196,30 @@ bool X86WinEHUnwindV2::runOnMachineFunction(MachineFunction &MF) {
         State = FunctionState::FinishedEpilog;
         break;
 
-      case X86::LEA64r:
       case X86::MOV64rr:
+        if (State == FunctionState::InEpilog) {
+          // If the prolog contains a stack allocation, then the first
+          // instruction in the epilog must be to adjust the stack pointer.
+          if (!HasSetFrame)
+            return rejectCurrentFunctionInternalError(
+                MF, Mode,
+                "The epilog is setting frame back, but prolog did not set it");
+          if (PoppedRegCount > 0)
+            return rejectCurrentFunctionInternalError(
+                MF, Mode,
+                "The epilog is setting the frame back after popping "
+                "registers");
+          if (HasStackDealloc)
+            return rejectCurrentFunctionInternalError(
+                MF, Mode,
+                "Cannot set the frame back after the stack "
+                "allocation has been deallocated");
+        } else if (State == FunctionState::FinishedEpilog)
+          return rejectCurrentFunctionInternalError(
+              MF, Mode, "Unexpected mov instruction after the epilog");
+        break;
+
+      case X86::LEA64r:
----------------
efriedma-quic wrote:

Can an LEA64r correspond to a SetFrame?  (I think we might generate `lea 16(%rbp), %rsp` or something like that.)  Not sure how much it matters.

https://github.com/llvm/llvm-project/pull/154834