[Debug] LCSSA: Insert dbg.value at the first available insertion point

Inserting a dbg.value instruction at the start of a basic block with a
landingpad instruction triggers a verifier failure. We should be OK if
we insert the instruction a bit later.

Speculative fix for the bot failure described here:
https://reviews.llvm.org/D42551

llvm-svn: 323482

2 files changed, 7 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index a7eaffd1a7a..337ee0e9ef5 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -1373,7 +1373,9 @@ void llvm::insertDebugValuesForPHIs(BasicBlock *BB,
         auto PhiMAV = MetadataAsValue::get(C, ValueAsMetadata::get(PHI));
         NewDbgII->setOperand(0, PhiMAV);
         BasicBlock *Parent = PHI->getParent();
-        NewDbgII->insertBefore(Parent->getFirstNonPHIOrDbgOrLifetime());
+        auto InsertionPt = Parent->getFirstInsertionPt();
+        assert(InsertionPt != Parent->end() && "Ill-formed basic block");
+        NewDbgII->insertBefore(&*InsertionPt);
       }
     }
   }
diff --git a/llvm/test/Transforms/LCSSA/basictest.ll b/llvm/test/Transforms/LCSSA/basictest.ll
index 284de862eec..e5f974ca28d 100644
--- a/llvm/test/Transforms/LCSSA/basictest.ll
+++ b/llvm/test/Transforms/LCSSA/basictest.ll
@@ -19,8 +19,11 @@ post.if:		; preds = %if.false, %if.true
 	br i1 %S2, label %loop.exit, label %loop.interior
 loop.exit:		; preds = %post.if
 ; CHECK: %X3.lcssa = phi i32
-; CHECK2: call void @llvm.dbg.value(metadata i32 %X3.lcssa, metadata !11, metadata !DIExpression()), !dbg !19
 ; CHECK: %X4 = add i32 3, %X3.lcssa
+
+; CHECK2: call void @llvm.dbg.value(metadata i32 %X3.lcssa, metadata !11, metadata !DIExpression()), !dbg !19
+; CHECK2-NEXT: add i32 3, %X3.lcssa
+; CHECK2: ret void
 	%X4 = add i32 3, %X3		; <i32> [#uses=0]
 	ret void
 }