[PATCH] D60004: [WebAssembly] Handle END_LOOP is in unreachable BB in CFGStackify

[Heejin Ahn via Phabricator via llvm-commits]

aheejin created this revision.
aheejin added a reviewer: yurydelendik.
Herald added subscribers: llvm-commits, sunfish, jgravelle-google, sbc100, dschuff.
Herald added a project: LLVM.

This fixes crashes when a BB in which an END_LOOP is to be placed is
unreachable and does not have any predecessors.


Repository:
  rL LLVM

https://reviews.llvm.org/D60004

Files:
  lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
  test/CodeGen/WebAssembly/cfg-stackify-dbg.mir


Index: test/CodeGen/WebAssembly/cfg-stackify-dbg.mir
===================================================================
--- /dev/null
+++ test/CodeGen/WebAssembly/cfg-stackify-dbg.mir
@@ -0,0 +1,27 @@
+# RUN: llc -mtriple=wasm32-unknown-unknown -run-pass wasm-cfg-stackify %s -o - | FileCheck %s
+
+# This tests if END_LOOP marker is placed correctly when the BB it is to be
+# placed is unreachable.
+
+# CHECK-LABEL: eh_label_test
+name: eh_label_test
+liveins:
+  - { reg: '$arguments' }
+body: |
+  bb.0:
+    successors: %bb.1
+
+  bb.1:
+  ; predecessors: %bb.0, %bb.2
+    successors: %bb.2
+
+  bb.2:
+  ; predecessors: %bb.1
+    successors: %bb.1
+    BR %bb.1, implicit-def dead $arguments
+
+  ; CHECK: bb.3
+  ; CHECK: END_LOOP
+  bb.3:
+    UNREACHABLE implicit-def $arguments
+...
Index: lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
===================================================================
--- lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
+++ lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
@@ -411,7 +411,9 @@
   // Mark the end of the loop (using arbitrary debug location that branched to
   // the loop end as its location).
   InsertPos = getEarliestInsertPos(AfterLoop, BeforeSet, AfterSet);
-  DebugLoc EndDL = (*AfterLoop->pred_rbegin())->findBranchDebugLoc();
+  DebugLoc EndDL = AfterLoop->pred_empty()
+                       ? DebugLoc()
+                       : (*AfterLoop->pred_rbegin())->findBranchDebugLoc();
   MachineInstr *End =
       BuildMI(*AfterLoop, InsertPos, EndDL, TII.get(WebAssembly::END_LOOP));
   registerScope(Begin, End);


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