From 5c6c5e23bd4282928c83d17aca95b5d31e7c2d0b Mon Sep 17 00:00:00 2001
From: Hans Wennborg <hans@hanshq.net>
Date: Sat, 29 Nov 2014 21:17:05 +0000
Subject: [PATCH] Switch lowering: Fix broken 'Figure out which block is next'
 code

This doesn't seem to have worked in a long time, but other optimizations
would clean it up.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222961 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp |  3 +++
 test/CodeGen/X86/switch-default-only.ll          | 14 ++++++++++++++
 test/DebugInfo/unconditional-branch.ll           |  5 +++--
 3 files changed, 20 insertions(+), 2 deletions(-)
 create mode 100644 test/CodeGen/X86/switch-default-only.ll

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 8f582f1aeb6..196d26d50ed 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -2694,6 +2694,9 @@ void SelectionDAGBuilder::visitSwitch(const SwitchInst &SI) {
 
   // Figure out which block is immediately after the current one.
   MachineBasicBlock *NextBlock = nullptr;
+  if (SwitchMBB + 1 != FuncInfo.MF->end())
+    NextBlock = SwitchMBB + 1;
+
   MachineBasicBlock *Default = FuncInfo.MBBMap[SI.getDefaultDest()];
 
   // If there is only the default destination, branch to it if it is not the
diff --git a/test/CodeGen/X86/switch-default-only.ll b/test/CodeGen/X86/switch-default-only.ll
new file mode 100644
index 00000000000..360ace5b787
--- /dev/null
+++ b/test/CodeGen/X86/switch-default-only.ll
@@ -0,0 +1,14 @@
+; RUN: llc -O0 -fast-isel=false -march=x86 < %s | FileCheck %s
+
+; No need for branching when the default and only destination follows
+; immediately after the switch.
+; CHECK-LABEL: no_branch:
+; CHECK-NOT: jmp
+; CHECK: ret
+
+define void @no_branch(i32 %x) {
+entry:
+  switch i32 %x, label %exit [ ]
+exit:
+  ret void
+}
diff --git a/test/DebugInfo/unconditional-branch.ll b/test/DebugInfo/unconditional-branch.ll
index 95f5f9ef1c2..f7998d207f4 100644
--- a/test/DebugInfo/unconditional-branch.ll
+++ b/test/DebugInfo/unconditional-branch.ll
@@ -27,11 +27,12 @@ entry:
   switch i32 %0, label %sw.default [
   ], !dbg !14
 
+sw.epilog:                                        ; preds = %sw.default
+  ret void, !dbg !17
+
 sw.default:                                       ; preds = %entry
   br label %sw.epilog, !dbg !15
 
-sw.epilog:                                        ; preds = %sw.default
-  ret void, !dbg !17
 }
 
 ; Function Attrs: nounwind readnone
-- 
2.34.1