[BasicBlockUtils] Use getFirstNonPHIOrDbg to set debugloc for instructions created in SplitBlockPredecessors

Summary:
When setting debugloc for instructions created in SplitBlockPredecessors, current implementation copies debugloc from the first-non-phi instruction of the original basic block. However, if the first-non-phi instruction is a call for @llvm.dbg.value, the debugloc of the instruction may point the location outside of the block itself. For the example code of

```
  1 typedef struct _node_t {
  2   struct _node_t *next;
  3 } node_t;
  4
  5 extern node_t *root;
  6
  7 int foo() {
  8   node_t *node, *tmp;
  9   int ret = 0;
 10
 11   node = tmp = root->next;
 12   while (node != root) {
 13     while (node) {
 14       tmp = node;
 15       node = node->next;
 16       ret++;
 17     }
 18   }
 19
 20   return ret;
 21 }
```

, below is the basicblock corresponding to line 12 after Reassociate expressions pass:

```
while.cond:                                       ; preds = %while.cond2, %entry
  %node.0 = phi %struct._node_t* [ %1, %entry ], [ null, %while.cond2 ]
  %ret.0 = phi i32 [ 0, %entry ], [ %ret.1, %while.cond2 ]
  tail call void @llvm.dbg.value(metadata i32 %ret.0, i64 0, metadata !19, metadata !20), !dbg !21
  tail call void @llvm.dbg.value(metadata %struct._node_t* %node.0, i64 0, metadata !11, metadata !20), !dbg !31
  %cmp = icmp eq %struct._node_t* %node.0, %0, !dbg !33
  br i1 %cmp, label %while.end5, label %while.cond2, !dbg !35
```

As you can see, the first-non-phi instruction is a call for @llvm.dbg.value, and the debugloc is

```
!21 = !DILocation(line: 9, column: 7, scope: !6)
```

, which is a definition of 'ret' variable and outside of the scope of the basicblock itself. However, current implementation picks up this debugloc for the instructions created in SplitBlockPredecessors. This patch addresses this problem by picking up debugloc from the first-non-phi-non-dbg instruction.

Reviewers: dblaikie, samsonov, eugenis

Reviewed By: eugenis

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D29867

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@295106 91177308-0d34-0410-b5e6-96231b3b80d8

Author: taewookoh

lib/Transforms/Utils/BasicBlockUtils.cpp

@@ -438,7 +438,7 @@ BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
 
   // The new block unconditionally branches to the old block.
   BranchInst *BI = BranchInst::Create(BB, NewBB);
-  BI->setDebugLoc(BB->getFirstNonPHI()->getDebugLoc());
+  BI->setDebugLoc(BB->getFirstNonPHIOrDbg()->getDebugLoc());
 
   // Move the edges from Preds to point to NewBB instead of BB.
   for (unsigned i = 0, e = Preds.size(); i != e; ++i) {

test/Transforms/LoopSimplify/dbg-loc.ll

@@ -23,6 +23,7 @@ entry:
 
 for.body:                                         ; preds = %entry, %length.exit
   %begin.sink5 = phi %"Length"* [ %incdec.ptr, %length.exit ], [ %begin, %entry ]
+  tail call void @llvm.dbg.value(metadata %"Length"* %begin.sink5, i64 0, metadata !15, metadata !16), !dbg !17
   %m_type.i.i.i = getelementptr inbounds %"Length", %"Length"* %begin.sink5, i64 0, i32 2, !dbg !9
   %0 = load i8, i8* %m_type.i.i.i, align 1, !dbg !9
   %cmp.i.i = icmp eq i8 %0, 9, !dbg !7
@@ -68,6 +69,9 @@ eh.resume:                                        ; preds = %catch
   resume { i8*, i32 } undef, !dbg !13
 }
 
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata)
+
 ; CHECK-DAG: [[PREHEADER_LOC]] = !DILocation(line: 73, column: 27, scope: !{{[0-9]+}})
 ; CHECK-DAG: [[LOOPEXIT_LOC]] = !DILocation(line: 75, column: 9, scope: !{{[0-9]+}})
 ; CHECK-DAG: [[LPAD_PREHEADER_LOC]] = !DILocation(line: 85, column: 1, scope: !{{[0-9]+}})
@@ -93,3 +97,6 @@ eh.resume:                                        ; preds = %catch
                              file: !5,
                              isOptimized: true, flags: "-O2",
                              splitDebugFilename: "abc.debug", emissionKind: 2)
+!15 = !DILocalVariable(name: "begin", arg: 1, scope: !6, file: !5, line: 71)
+!16 = !DIExpression()
+!17 = !DILocation(line: 71, column: 32, scope: !6)