[MC] [Win64EH] Fix the calculation of the end of epilogs

Exclude the terminating end opcode from the epilog - it doesn't
correspond to an actual instruction that is included in the epilog
itself (within the .seh_startepilogue/.seh_endepilogue range).

In most (all?) cases, an epilog is followed by a matching terminating
instruction though (a ret or a branch to a tail call), but it's not
strictly within the .seh_startepilogue/.seh_endepilogue range.

This fixes a number of failed asserts in cases where the codegen
has incorrectly reoredered SEH opcodes so they don't match up
exactly with their instructions.

However this still just avoids failing the assertion; the root cause
of generating unexpected epilogs is still present (and fixing that is
a less obvious issue).

Differential Revision: https://reviews.llvm.org/D131393

1 files changed, 3 insertions, 1 deletions

diff --git a/llvm/lib/MC/MCWin64EH.cpp b/llvm/lib/MC/MCWin64EH.cpp
index 8f53ab1..ff1c1ad 100644
--- a/llvm/lib/MC/MCWin64EH.cpp
+++ b/llvm/lib/MC/MCWin64EH.cpp
@@ -997,7 +997,9 @@ static void ARM64FindSegmentsInFunction(MCStreamer &streamer,
     int64_t Offset = GetAbsDifference(streamer, Start, info->Begin);
     assert((Epilogs.size() == 0 || Offset >= Epilogs.back().End) &&
            "Epilogs should be monotonically ordered");
-    Epilogs.push_back({Start, Offset, Offset + (int64_t)Instrs.size() * 4});
+    // Exclue the end opcode from Instrs.size() when calculating the end of the
+    // epilog.
+    Epilogs.push_back({Start, Offset, Offset + (int64_t)(Instrs.size() - 1) * 4});
   }
 
   unsigned E = 0;