From 2dbff99e43a082c76202cfafb8f5da40f11c94dc Mon Sep 17 00:00:00 2001
From: Heejin Ahn <aheejin@gmail.com>
Date: Fri, 29 Mar 2019 19:36:51 +0000
Subject: [PATCH] [WebAssembly] Handle END_LOOP in unreachable BB in
 CFGStackify

Summary:
This fixes crashes when a BB in which an END_LOOP is to be placed is
unreachable and does not have any predecessors. Fixes PR41307.

Reviewers: dschuff

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D60004

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@357303 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../WebAssembly/WebAssemblyCFGStackify.cpp    |  4 ++-
 test/CodeGen/WebAssembly/cfg-stackify-dbg.mir | 27 +++++++++++++++++++
 2 files changed, 30 insertions(+), 1 deletion(-)
 create mode 100644 test/CodeGen/WebAssembly/cfg-stackify-dbg.mir

diff --git a/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp b/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
index 39641b414cb..b64aa3023bb 100644
--- a/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
+++ b/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
@@ -411,7 +411,9 @@ void WebAssemblyCFGStackify::placeLoopMarker(MachineBasicBlock &MBB) {
   // 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);
diff --git a/test/CodeGen/WebAssembly/cfg-stackify-dbg.mir b/test/CodeGen/WebAssembly/cfg-stackify-dbg.mir
new file mode 100644
index 00000000000..cd76d9132f9
--- /dev/null
+++ b/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. Regression test for PR41307.
+
+# CHECK-LABEL: unreachable_test
+name: unreachable_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
+...
-- 
2.50.1