From 08c6feac7d1cebedeb651479712badef7e0ca71f Mon Sep 17 00:00:00 2001
From: Jessica Paquette <jpaquette@apple.com>
Date: Fri, 4 Oct 2019 21:24:12 +0000
Subject: [PATCH] [MachineOutliner] Disable outlining from noreturn functions

Outlining from noreturn functions doesn't do the correct thing right now. The
outliner should respect that the caller is marked noreturn. In the event that
we have a noreturn function, and the outlined code is in tail position, the
outliner will not see that the outlined function should be tail called. As a
result, you end up with a regular call containing a return.

Fixing this requires that we check that all candidates live inside noreturn
functions. So, for the sake of correctness, don't outline from noreturn
functions right now.

Add machine-outliner-noreturn.mir to test this.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@373791 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/MachineOutliner.cpp               |  6 ++
 .../AArch64/machine-outliner-noreturn.mir     | 56 +++++++++++++++++++
 2 files changed, 62 insertions(+)
 create mode 100644 test/CodeGen/AArch64/machine-outliner-noreturn.mir

diff --git a/lib/CodeGen/MachineOutliner.cpp b/lib/CodeGen/MachineOutliner.cpp
index 533cce57adc..60eeefba9d6 100644
--- a/lib/CodeGen/MachineOutliner.cpp
+++ b/lib/CodeGen/MachineOutliner.cpp
@@ -1303,6 +1303,12 @@ void MachineOutliner::populateMapper(InstructionMapper &Mapper, Module &M,
     if (F.empty())
       continue;
 
+    // Disable outlining from noreturn functions right now. Noreturn requires
+    // special handling for the case where what we are outlining could be a
+    // tail call.
+    if (F.hasFnAttribute(Attribute::NoReturn))
+      continue;
+
     // There's something in F. Check if it has a MachineFunction associated with
     // it.
     MachineFunction *MF = MMI.getMachineFunction(F);
diff --git a/test/CodeGen/AArch64/machine-outliner-noreturn.mir b/test/CodeGen/AArch64/machine-outliner-noreturn.mir
new file mode 100644
index 00000000000..29166f9f12d
--- /dev/null
+++ b/test/CodeGen/AArch64/machine-outliner-noreturn.mir
@@ -0,0 +1,56 @@
+# RUN: llc -mtriple=aarch64-unknown-unknown -run-pass=machine-outliner -verify-machineinstrs %s -o - | FileCheck %s
+
+--- |
+  define void @foo() #0 { ret void }
+  define void @bar(i32 %a) #0 { ret void }
+  define void @baz(i32 %a) #0 { ret void }
+  attributes #0 = { noredzone noreturn }
+...
+---
+
+# Temporarily disable outlining from noreturn functions. To do this, we need
+# to verify thst every function we want to outline from is noreturn.
+
+# CHECK-NOT: OUTLINED_FUNCTION
+
+name:            foo
+alignment:       4
+tracksRegLiveness: true
+frameInfo:
+  maxAlignment:    1
+  maxCallFrameSize: 0
+machineFunctionInfo: {}
+body:             |
+  bb.0:
+    $w3 = ORRWri $wzr, 1
+    $w4 = ORRWri $wzr, 1
+    BRK 1
+...
+---
+name:            bar
+alignment:       4
+tracksRegLiveness: true
+frameInfo:
+  maxAlignment:    1
+  maxCallFrameSize: 0
+machineFunctionInfo: {}
+body:             |
+  bb.0:
+    $w3 = ORRWri $wzr, 1
+    $w4 = ORRWri $wzr, 1
+    BRK 1
+...
+---
+name:            baz
+alignment:       4
+tracksRegLiveness: true
+frameInfo:
+  maxAlignment:    1
+  maxCallFrameSize: 0
+machineFunctionInfo: {}
+body:             |
+  bb.0:
+    $w3 = ORRWri $wzr, 1
+    $w4 = ORRWri $wzr, 1
+    BRK 1
+...
-- 
2.40.0