[WebAssembly] Handle empty cleanuppads when adding catch_all

[aheejin]

Summary

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.

llvm/lib/Target/WebAssembly/WebAssemblyLateEHPrepare.cpp

for (auto &MBB : MF) {
     // Skip EH_LABELs in the beginning of an EH pad if present.
     while (InsertPos != MBB.end() && InsertPos->isEHLabel())
       InsertPos++;
     // This runs after hoistCatches(), so we assume that if there is a catch,
     // that should be the first non-EH-label instruction in an EH pad.
     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));
     }
   }
   return Changed;
 }
 
 // Replace pseudo-instructions catchret and cleanupret with br and rethrow
 // respectively.

llvm/test/CodeGen/WebAssembly/exception.mir

 # RUN: llc -mtriple=wasm32-unknown-unknown -exception-model=wasm -mattr=+exception-handling -run-pass wasm-late-eh-prepare -run-pass wasm-cfg-stackify %s -o - | FileCheck %s
 
 --- |
   target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
   target triple = "wasm32-unknown-unknown"
 
   declare i32 @__gxx_wasm_personality_v0(...)
   declare void @foo()
   define void @eh_label_test() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
     ret void
   }
   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
+  }
 ...
 
 ---
 # This tests 'try' and 'catch' instructions are correctly placed with respect to
 # EH_LABEL instructions.
 # CHECK-LABEL: name: eh_label_test
 name: eh_label_test
 liveins:
bb.1 (landing-pad):
     EH_LABEL <mcsymbol .Ltmp2>
     CATCHRET %bb.2, %bb.1, implicit-def dead $arguments
 
   ; CHECK: bb.2
   bb.2:
   ; 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
+...