[WebAssembly] Fix unwind destination mismatches in CFG stackify

Summary:
Linearing the control flow by placing `try`/`end_try` markers can create
mismatches in unwind destinations. This patch resolves these mismatches
by wrapping those instructions with an incorrect unwind destination with
a nested `try`/`catch`/`end_try` and branching to the right destination
within the new catch block.

Reviewers: dschuff

Subscribers: sunfish, sbc100, jgravelle-google, chrib, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D48345

llvm-svn: 357343

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyUtilities.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyUtilities.cpp
index 4edd546..002246a 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyUtilities.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyUtilities.cpp
@@ -64,6 +64,8 @@ bool WebAssembly::isCopy(const MachineInstr &MI) {
   case WebAssembly::COPY_F64_S:
   case WebAssembly::COPY_V128:
   case WebAssembly::COPY_V128_S:
+  case WebAssembly::COPY_EXCEPT_REF:
+  case WebAssembly::COPY_EXCEPT_REF_S:
     return true;
   default:
     return false;
@@ -266,5 +268,8 @@ bool WebAssembly::mayThrow(const MachineInstr &MI) {
   if (F->getName() == CxaBeginCatchFn || F->getName() == PersonalityWrapperFn ||
       F->getName() == ClangCallTerminateFn || F->getName() == StdTerminateFn)
     return false;
+
+  // TODO Can we exclude call instructions that are marked as 'nounwind' in the
+  // original LLVm IR? (Even when the callee may throw)
   return true;
 }