From 4a4d245b194d56b74bbb9012d25b44aaba753e36 Mon Sep 17 00:00:00 2001
From: Sebastian Pop <sebpop@gmail.com>
Date: Wed, 8 Mar 2017 01:54:50 +0000
Subject: [PATCH] Handle UnreachableInst in
 isGuaranteedToTransferExecutionToSuccessor

A block with an UnreachableInst does not transfer execution to a successor.
The problem was exposed by GVN-hoist. This patch fixes bug 32153.

Patch by Aditya Kumar.

Differential Revision: https://reviews.llvm.org/D30667

llvm-svn: 297254
---
 llvm/lib/Analysis/ValueTracking.cpp           |  2 ++
 .../Transforms/GVNHoist/hoist-very-busy.ll    | 34 +++++++++++++++++++
 2 files changed, 36 insertions(+)
 create mode 100644 llvm/test/Transforms/GVNHoist/hoist-very-busy.ll

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 70fab29087f9..1761dac269d0 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -3781,6 +3781,8 @@ bool llvm::isGuaranteedToTransferExecutionToSuccessor(const Instruction *I) {
     return false;
   if (isa<ReturnInst>(I))
     return false;
+  if (isa<UnreachableInst>(I))
+    return false;
 
   // Calls can throw, or contain an infinite loop, or kill the process.
   if (auto CS = ImmutableCallSite(I)) {
diff --git a/llvm/test/Transforms/GVNHoist/hoist-very-busy.ll b/llvm/test/Transforms/GVNHoist/hoist-very-busy.ll
new file mode 100644
index 000000000000..b2751fb6feb6
--- /dev/null
+++ b/llvm/test/Transforms/GVNHoist/hoist-very-busy.ll
@@ -0,0 +1,34 @@
+; RUN: opt -S -gvn-hoist < %s | FileCheck %s
+
+%struct.__jmp_buf_tag = type { [8 x i64], i32 }
+
+; Check that hoisting only happens when the expression is very busy.
+; CHECK: store
+; CHECK: store
+
+@test_exit_buf = global %struct.__jmp_buf_tag zeroinitializer
+@G = global i32 0
+
+define void @test_command(i32 %c1) {
+entry:
+  switch i32 %c1, label %exit [
+    i32 0, label %sw0
+    i32 1, label %sw1
+  ]
+
+sw0:
+  store i32 1, i32* @G
+  br label %exit
+
+sw1:
+  store i32 1, i32* @G
+  br label %exit
+
+exit:
+  call void @longjmp(%struct.__jmp_buf_tag* @test_exit_buf, i32 1) #0
+  unreachable
+}
+
+declare void @longjmp(%struct.__jmp_buf_tag*, i32) #0
+
+attributes #0 = { noreturn nounwind }