From 71adee46e424dc5ab6c632db9a72b63258208955 Mon Sep 17 00:00:00 2001
From: Dylan McKay <me@dylanmckay.io>
Date: Tue, 4 Jul 2017 04:40:06 +0000
Subject: [PATCH] [AVR] Fix bug which caused assertion errors for some FRMIDX
 instructions

Previously, if a basic block ended with a FRMIDX instruction, we would
end up doing something like this.

*std::next(MBB.end())

Which would hit an error:

"Assertion `!NodePtr->isKnownSentinel()' failed."

llvm-svn: 307057
---
 lib/Target/AVR/AVRRegisterInfo.cpp      | 11 ++++++---
 test/CodeGen/AVR/frmidx-iterator-bug.ll | 33 +++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 3 deletions(-)
 create mode 100644 test/CodeGen/AVR/frmidx-iterator-bug.ll

diff --git a/lib/Target/AVR/AVRRegisterInfo.cpp b/lib/Target/AVR/AVRRegisterInfo.cpp
index 55f3f5cf428..249dc5512c2 100644
--- a/lib/Target/AVR/AVRRegisterInfo.cpp
+++ b/lib/Target/AVR/AVRRegisterInfo.cpp
@@ -95,7 +95,8 @@ AVRRegisterInfo::getLargestLegalSuperClass(const TargetRegisterClass *RC,
 }
 
 /// Fold a frame offset shared between two add instructions into a single one.
-static void foldFrameOffset(MachineInstr &MI, int &Offset, unsigned DstReg) {
+static void foldFrameOffset(MachineBasicBlock::iterator &II, int &Offset, unsigned DstReg) {
+  MachineInstr &MI = *II;
   int Opcode = MI.getOpcode();
 
   // Don't bother trying if the next instruction is not an add or a sub.
@@ -120,6 +121,7 @@ static void foldFrameOffset(MachineInstr &MI, int &Offset, unsigned DstReg) {
   }
 
   // Finally remove the instruction.
+  II++;
   MI.eraseFromParent();
 }
 
@@ -158,6 +160,8 @@ void AVRRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
     unsigned DstReg = MI.getOperand(0).getReg();
     assert(DstReg != AVR::R29R28 && "Dest reg cannot be the frame pointer");
 
+    II++; // Skip over the FRMIDX (and now MOVW) instruction.
+
     // Generally, to load a frame address two add instructions are emitted that
     // could get folded into a single one:
     //  movw    r31:r30, r29:r28
@@ -166,7 +170,8 @@ void AVRRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
     // to:
     //  movw    r31:r30, r29:r28
     //  adiw    r31:r30, 45
-    foldFrameOffset(*std::next(II), Offset, DstReg);
+    if (II != MBB.end())
+      foldFrameOffset(II, Offset, DstReg);
 
     // Select the best opcode based on DstReg and the offset size.
     switch (DstReg) {
@@ -187,7 +192,7 @@ void AVRRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
     }
     }
 
-    MachineInstr *New = BuildMI(MBB, std::next(II), dl, TII.get(Opcode), DstReg)
+    MachineInstr *New = BuildMI(MBB, II, dl, TII.get(Opcode), DstReg)
                             .addReg(DstReg, RegState::Kill)
                             .addImm(Offset);
     New->getOperand(3).setIsDead();
diff --git a/test/CodeGen/AVR/frmidx-iterator-bug.ll b/test/CodeGen/AVR/frmidx-iterator-bug.ll
new file mode 100644
index 00000000000..f9e2f0688fa
--- /dev/null
+++ b/test/CodeGen/AVR/frmidx-iterator-bug.ll
@@ -0,0 +1,33 @@
+; RUN: llc < %s -march=avr -mattr=avr6 | FileCheck %s
+
+%str_slice = type { i8*, i16 }
+%Machine = type { i16, [0 x i8], i16, [0 x i8], [16 x i8], [0 x i8] }
+
+; CHECK-LABEL: step
+define void @step(%Machine*) {
+ ret void
+}
+
+; CHECK-LABEL: main
+define void @main() {
+start:
+  %machine = alloca %Machine, align 8
+  %v0 = bitcast %Machine* %machine to i8*
+  %v1 = getelementptr inbounds %Machine, %Machine* %machine, i16 0, i32 2
+  %v2 = load i16, i16* %v1, align 2
+  br label %bb2.i5
+
+bb2.i5:
+  %v18 = load volatile i8, i8* inttoptr (i16 77 to i8*), align 1
+  %v19 = icmp sgt i8 %v18, -1
+  br i1 %v19, label %bb2.i5, label %bb.exit6
+
+bb.exit6:
+  %v20 = load volatile i8, i8* inttoptr (i16 78 to i8*), align 2
+  br label %bb7
+
+bb7:
+  call void @step(%Machine* %machine)
+  br label %bb7
+}
+