From 4ef730d369814be3cc8533c05f14ff1b25b95f61 Mon Sep 17 00:00:00 2001
From: Sanne Wouda <sanne.wouda@arm.com>
Date: Mon, 13 Feb 2017 14:07:45 +0000
Subject: [PATCH] [CodeGen] fix alignment of JUMPTABLE_INSTS on v8M.base

Summary:
The attached test case fails with "fatal error: error in backend:
misaligned pc-relative fixup value" as the jump table is misaligned.
The EmitAlignment existed already for ARM and Thumb-1 code, but was
missing for Thumb-2.

The test checks that the fatal error disappears when generating an obj
file, as well as checking the align directive is there when producing an
asm file.


Reviewers: rengolin, grosbach, t.p.northover, jmolloy, SjoerdMeijer, samparker

Reviewed By: samparker

Subscribers: samparker, aemerson, llvm-commits

Differential Revision: https://reviews.llvm.org/D29650

llvm-svn: 294950
---
 lib/Target/ARM/ARMAsmPrinter.cpp              |  5 ++
 .../ARM/v8m.base-jumptable_alignment.ll       | 51 +++++++++++++++++++
 2 files changed, 56 insertions(+)
 create mode 100644 test/CodeGen/ARM/v8m.base-jumptable_alignment.ll

diff --git a/lib/Target/ARM/ARMAsmPrinter.cpp b/lib/Target/ARM/ARMAsmPrinter.cpp
index d77717e3ba2..eb0d410b596 100644
--- a/lib/Target/ARM/ARMAsmPrinter.cpp
+++ b/lib/Target/ARM/ARMAsmPrinter.cpp
@@ -1142,6 +1142,11 @@ void ARMAsmPrinter::EmitJumpTableInsts(const MachineInstr *MI) {
   const MachineOperand &MO1 = MI->getOperand(1);
   unsigned JTI = MO1.getIndex();
 
+  // Make sure the Thumb jump table is 4-byte aligned. This will be a nop for
+  // ARM mode tables.
+  EmitAlignment(2);
+
+  // Emit a label for the jump table.
   MCSymbol *JTISymbol = GetARMJTIPICJumpTableLabel(JTI);
   OutStreamer->EmitLabel(JTISymbol);
 
diff --git a/test/CodeGen/ARM/v8m.base-jumptable_alignment.ll b/test/CodeGen/ARM/v8m.base-jumptable_alignment.ll
new file mode 100644
index 00000000000..673e04687a1
--- /dev/null
+++ b/test/CodeGen/ARM/v8m.base-jumptable_alignment.ll
@@ -0,0 +1,51 @@
+; RUN: llc -filetype=obj -o /dev/null < %s
+; RUN: llc -filetype=asm < %s | FileCheck %s
+
+; ModuleID = 'bugpoint-reduced-simplified.bc'
+source_filename = "bugpoint-output-39ed676.bc"
+target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
+target triple = "thumbv8m.base-arm-none-eabi"
+
+@crc32_tab = external unnamed_addr global [256 x i32], align 4
+@g_566 = external global i32**, align 4
+
+define void @main() {
+entry:
+  %0 = load volatile i32**, i32*** @g_566, align 4
+  br label %func_16.exit.i.i.i
+
+lbl_1394.i.i.i.loopexit:                          ; preds = %for.cond14.preheader.us.i.i.i
+  unreachable
+
+func_16.exit.i.i.i:                               ; preds = %entry
+  br i1 undef, label %for.cond7.preheader.i.lr.ph.i.i, label %for.end476.i.i.i.loopexit
+
+for.cond7.preheader.i.lr.ph.i.i:                  ; preds = %func_16.exit.i.i.i
+  br i1 undef, label %for.end476.i.i.i.loopexit, label %for.cond7.preheader.i.i.preheader.i
+
+for.cond7.preheader.i.i.preheader.i:              ; preds = %for.cond7.preheader.i.lr.ph.i.i
+  br label %for.cond14.preheader.us.i.i.i
+
+for.cond7.preheader.i.us.i.i:                     ; preds = %for.cond7.preheader.i.lr.ph.i.i
+  unreachable
+
+for.cond14.preheader.us.i.i.i:                    ; preds = %for.inc459.us.i.i.i, %for.cond7.preheader.i.i.preheader.i
+; CHECK: @ BB#4
+; CHECK-NEXT: .p2align 2
+  switch i4 undef, label %func_1.exit.loopexit [
+    i4 0, label %for.inc459.us.i.i.i
+    i4 -5, label %for.inc459.us.i.i.i
+    i4 2, label %lbl_1394.i.i.i.loopexit
+    i4 3, label %for.end476.i.i.i.loopexit
+  ]
+
+for.inc459.us.i.i.i:                              ; preds = %for.cond14.preheader.us.i.i.i, %for.cond14.preheader.us.i.i.i
+  br label %for.cond14.preheader.us.i.i.i
+
+for.end476.i.i.i.loopexit:                        ; preds = %for.cond14.preheader.us.i.i.i
+  unreachable
+
+func_1.exit.loopexit:                             ; preds = %for.cond14.preheader.us.i.i.i
+  %arrayidx.i63.i.i5252 = getelementptr inbounds [256 x i32], [256 x i32]* @crc32_tab, i32 0, i32 undef
+  unreachable
+}