From 0c4debc123b3cf92d018700a26a32ae5fc39a7b9 Mon Sep 17 00:00:00 2001
From: Dylan McKay <me@dylanmckay.io>
Date: Sat, 13 May 2017 00:22:34 +0000
Subject: [PATCH] [AVR] When lowering Select8/Select16, put newly generated
 MBBs in the same spot
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Contributed by Dr. Gergő Érdi.

Fixes a bug.

Raised from (https://github.com/avr-rust/rust/issues/49).

llvm-svn: 302973
---
 llvm/lib/Target/AVR/AVRISelLowering.cpp           |  5 ++--
 llvm/test/CodeGen/AVR/select-mbb-placement-bug.ll | 35 +++++++++++++++++++++++
 2 files changed, 38 insertions(+), 2 deletions(-)
 create mode 100644 llvm/test/CodeGen/AVR/select-mbb-placement-bug.ll

diff --git a/llvm/lib/Target/AVR/AVRISelLowering.cpp b/llvm/lib/Target/AVR/AVRISelLowering.cpp
index 0d8c44e..ef9c00e 100644
--- a/llvm/lib/Target/AVR/AVRISelLowering.cpp
+++ b/llvm/lib/Target/AVR/AVRISelLowering.cpp
@@ -1610,8 +1610,9 @@ AVRTargetLowering::EmitInstrWithCustomInserter(MachineInstr &MI,
   MachineBasicBlock *trueMBB = MF->CreateMachineBasicBlock(LLVM_BB);
   MachineBasicBlock *falseMBB = MF->CreateMachineBasicBlock(LLVM_BB);
 
-  MachineFunction::iterator I = MBB->getParent()->begin();
-  ++I;
+  MachineFunction::iterator I;
+  for (I = MF->begin(); I != MF->end() && &(*I) != MBB; ++I);
+  if (I != MF->end()) ++I;
   MF->insert(I, trueMBB);
   MF->insert(I, falseMBB);
 
diff --git a/llvm/test/CodeGen/AVR/select-mbb-placement-bug.ll b/llvm/test/CodeGen/AVR/select-mbb-placement-bug.ll
new file mode 100644
index 0000000..ca7ec1a
--- /dev/null
+++ b/llvm/test/CodeGen/AVR/select-mbb-placement-bug.ll
@@ -0,0 +1,35 @@
+; RUN: llc -mcpu=atmega328p < %s -march=avr | FileCheck %s
+
+; CHECK-LABEL: loopy
+define internal fastcc void @loopy() {
+
+; In this case, when we expand `Select8`/`Select16`, we should be
+; replacing the existing MBB instead of adding a new one.
+;
+; https://github.com/avr-rust/rust/issues/49
+
+; CHECK: LBB0_1:
+; CHECK: LBB0_2:
+; CHECK-NOT: LBB0_3:
+start:
+  br label %bb7.preheader
+
+bb7.preheader:                                    ; preds = %bb10, %start
+  %i = phi i8 [ 0, %start ], [ %j, %bb10 ]
+  %j = phi i8 [ 1, %start ], [ %next, %bb10 ]
+  br label %bb10
+
+bb4:                                              ; preds = %bb10
+  ret void
+
+bb10:                                             ; preds = %bb7.preheader
+  tail call fastcc void @observe(i8 %i, i8 1)
+  %0 = icmp ult i8 %j, 20
+  %1 = zext i1 %0 to i8
+  %next = add i8 %j, %1
+  br i1 %0, label %bb7.preheader, label %bb4
+
+}
+
+declare void @observe(i8, i8);
+
-- 
2.7.4