Fix for PR 19261:

llc doesn't generate nodes for unconditional fall-through branches for targets
without FastISel implementation (X86 has it, but can be disabled by
"-fast-isel=false") in SelectionDAGBuilder::visitBr().

So for line 4 in the following testcase

1: void foo(int i){
2:   switch(i){
3:   default:
4:     break;
5:   }
6:   return;
7: }

there is no corresponding line in .debug_line section, and a debugger
cannot set a breakpoint at line 4.

Fix this by always emitting a branch when we're not optimizing and add a
testcase to ensure that there's code on every line we'd want to break.

Patch by Daniil Fukalov.

llvm-svn: 205529

1 files changed, 3 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 604ff70f923..4a6e5cf0361 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -1571,8 +1571,9 @@ void SelectionDAGBuilder::visitBr(const BranchInst &I) {
     // Update machine-CFG edges.
     BrMBB->addSuccessor(Succ0MBB);
 
-    // If this is not a fall-through branch, emit the branch.
-    if (Succ0MBB != NextBlock)
+    // If this is not a fall-through branch or optimizations are switched off,
+    // emit the branch.
+    if (Succ0MBB != NextBlock || TM.getOptLevel() == CodeGenOpt::None)
       DAG.setRoot(DAG.getNode(ISD::BR, getCurSDLoc(),
                               MVT::Other, getControlRoot(),
                               DAG.getBasicBlock(Succ0MBB)));