From 68037e84f0879dd5b05d9a4090ae2c2610c0642b Mon Sep 17 00:00:00 2001
From: Krzysztof Parzyszek <kparzysz@codeaurora.org>
Date: Fri, 28 Apr 2017 21:54:11 +0000
Subject: [PATCH] [Hexagon] Do not move a block if it is on a fall-through path

llvm-svn: 301698
---
 lib/Target/Hexagon/HexagonCFGOptimizer.cpp  | 13 +++-
 test/CodeGen/Hexagon/cfgopt-fall-through.ll | 71 +++++++++++++++++++++
 2 files changed, 81 insertions(+), 3 deletions(-)
 create mode 100644 test/CodeGen/Hexagon/cfgopt-fall-through.ll

diff --git a/lib/Target/Hexagon/HexagonCFGOptimizer.cpp b/lib/Target/Hexagon/HexagonCFGOptimizer.cpp
index 2f8fe6e087f..c7b422e7efd 100644
--- a/lib/Target/Hexagon/HexagonCFGOptimizer.cpp
+++ b/lib/Target/Hexagon/HexagonCFGOptimizer.cpp
@@ -38,6 +38,7 @@ class HexagonCFGOptimizer : public MachineFunctionPass {
 
 private:
   void InvertAndChangeJumpTarget(MachineInstr &, MachineBasicBlock *);
+  bool isOnFallThroughPath(MachineBasicBlock *MBB);
 
 public:
   static char ID;
@@ -106,6 +107,14 @@ void HexagonCFGOptimizer::InvertAndChangeJumpTarget(
   MI.getOperand(1).setMBB(NewTarget);
 }
 
+bool HexagonCFGOptimizer::isOnFallThroughPath(MachineBasicBlock *MBB) {
+  if (MBB->canFallThrough())
+    return true;
+  for (MachineBasicBlock *PB : MBB->predecessors())
+    if (PB->isLayoutSuccessor(MBB) && PB->canFallThrough())
+      return true;
+  return false;
+}
 
 bool HexagonCFGOptimizer::runOnMachineFunction(MachineFunction &Fn) {
   if (skipFunction(*Fn.getFunction()))
@@ -182,7 +191,6 @@ bool HexagonCFGOptimizer::runOnMachineFunction(MachineFunction &Fn) {
         }
 
         if ((NumSuccs == 2) && LayoutSucc && (LayoutSucc->pred_size() == 1)) {
-
           // Ensure that BB2 has one instruction -- an unconditional jump.
           if ((LayoutSucc->size() == 1) &&
               IsUnconditionalJump(LayoutSucc->front().getOpcode())) {
@@ -211,9 +219,8 @@ bool HexagonCFGOptimizer::runOnMachineFunction(MachineFunction &Fn) {
                 JumpAroundTarget->moveAfter(LayoutSucc);
                 // only move a block if it doesn't have a fall-thru. otherwise
                 // the CFG will be incorrect.
-                if (!UncondTarget->canFallThrough()) {
+                if (!isOnFallThroughPath(UncondTarget))
                   UncondTarget->moveAfter(JumpAroundTarget);
-                }
               }
 
               //
diff --git a/test/CodeGen/Hexagon/cfgopt-fall-through.ll b/test/CodeGen/Hexagon/cfgopt-fall-through.ll
new file mode 100644
index 00000000000..be234aafc0b
--- /dev/null
+++ b/test/CodeGen/Hexagon/cfgopt-fall-through.ll
@@ -0,0 +1,71 @@
+; RUN: llc -march=hexagon -verify-machineinstrs < %s | FileCheck %s
+; REQUIRES: asserts
+
+; Check for some sane output. This test used to crash.
+; CHECK: jumpr r31
+
+
+define i32 @fred(i32 %a0, i8 zeroext %a1) local_unnamed_addr #0 {
+b2:
+  br i1 undef, label %b4, label %b3
+
+b3:                                               ; preds = %b2
+  unreachable
+
+b4:                                               ; preds = %b2
+  br i1 undef, label %b19, label %b5
+
+b5:                                               ; preds = %b4
+  br i1 undef, label %b6, label %b12
+
+b6:                                               ; preds = %b5
+  switch i8 %a1, label %b17 [
+    i8 2, label %b7
+    i8 5, label %b7
+    i8 1, label %b7
+    i8 3, label %b8
+  ]
+
+b7:                                               ; preds = %b6, %b6, %b6
+  unreachable
+
+b8:                                               ; preds = %b6
+  br i1 undef, label %b11, label %b9
+
+b9:                                               ; preds = %b8
+  %v10 = or i32 undef, 0
+  br label %b15
+
+b11:                                              ; preds = %b8
+  unreachable
+
+b12:                                              ; preds = %b5
+  switch i8 %a1, label %b17 [
+    i8 5, label %b13
+    i8 1, label %b13
+    i8 2, label %b14
+    i8 3, label %b15
+  ]
+
+b13:                                              ; preds = %b12, %b12
+  store i32 %a0, i32* undef, align 4
+  br label %b17
+
+b14:                                              ; preds = %b12
+  store i16 undef, i16* undef, align 4
+  br label %b17
+
+b15:                                              ; preds = %b12, %b9
+  %v16 = phi i32 [ 0, %b12 ], [ %v10, %b9 ]
+  store i32 undef, i32* undef, align 4
+  br label %b17
+
+b17:                                              ; preds = %b15, %b14, %b13, %b12, %b6
+  %v18 = phi i32 [ 0, %b13 ], [ 0, %b12 ], [ %v16, %b15 ], [ 0, %b14 ], [ 0, %b6 ]
+  ret i32 %v18
+
+b19:                                              ; preds = %b4
+  unreachable
+}
+
+attributes #0 = { nounwind "target-cpu"="hexagonv55" "target-features"="-hvx,-hvx-double,-long-calls" }