[WebAssembly] Handle empty cleanuppads when adding catch_all

In `LateEHPrepare::addCatchAlls`, the current code tries to get the
iterator's debug info even when it is `MachineBasicBlock::end()`. This
fixes the bug by adding empty debug info instead in that case.

Reviewed By: tlively

Differential Revision: https://reviews.llvm.org/D97679

Author: aheejin

llvm/lib/Target/WebAssembly/WebAssemblyLateEHPrepare.cpp

@@ -216,7 +216,8 @@ bool WebAssemblyLateEHPrepare::addCatchAlls(MachineFunction &MF) {
     if (InsertPos == MBB.end() ||
         !WebAssembly::isCatch(InsertPos->getOpcode())) {
       Changed = true;
-      BuildMI(MBB, InsertPos, InsertPos->getDebugLoc(),
+      BuildMI(MBB, InsertPos,
+              InsertPos == MBB.end() ? DebugLoc() : InsertPos->getDebugLoc(),
               TII.get(WebAssembly::CATCH_ALL));
     }
   }

llvm/test/CodeGen/WebAssembly/exception.mir

@@ -12,6 +12,9 @@
   define void @unreachable_ehpad_test() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
     ret void
   }
+  define void @empty_cleanuppad_test() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
+    ret void
+  }
 ...
 
 ---
@@ -81,3 +84,30 @@ body: |
   ; predecessors: %bb.0, %bb.1
     RETURN implicit-def dead $arguments
 ...
+
+---
+# Regression test for a bug that LateEHPrepare::addCatchAll didn't handle empty
+# cleanup pads. (It tried to get debug info from end() iterator.)
+name: empty_cleanuppad_test
+liveins:
+  - { reg: '$arguments' }
+body: |
+  bb.0:
+    successors: %bb.1, %bb.3
+    EH_LABEL <mcsymbol .Ltmp0>
+    CALL @foo, implicit-def dead $arguments, implicit $sp32, implicit $sp64
+    EH_LABEL <mcsymbol .Ltmp1>
+    BR %bb.3, implicit-def dead $arguments
+
+  ;; Empty cleanuppad
+  bb.1 (landing-pad):
+    successors: %bb.2
+    EH_LABEL <mcsymbol .Ltmp2>
+
+  bb.2:
+    successors: %bb.3
+    CLEANUPRET implicit-def dead $arguments
+
+  bb.3:
+    RETURN implicit-def dead $arguments
+...