[DebugInfo][Dexter] Speculated BB presents illegal variable value to debugger.

When SimplifyCFG changes the PHI node into a select instruction, the debug information becomes ambiguous. It causes the debugger to display wrong variable value. 

Differential Revision: https://reviews.llvm.org/D51976

llvm-svn: 342527

1 files changed, 6 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 422d1c9ef0a..493d1688226 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2370,15 +2370,19 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
   // Move all 'aggressive' instructions, which are defined in the
   // conditional parts of the if's up to the dominating block.
   if (IfBlock1) {
-    for (auto &I : *IfBlock1)
+    for (auto &I : *IfBlock1) {
       I.dropUnknownNonDebugMetadata();
+      dropDebugUsers(I);
+    }
     DomBlock->getInstList().splice(InsertPt->getIterator(),
                                    IfBlock1->getInstList(), IfBlock1->begin(),
                                    IfBlock1->getTerminator()->getIterator());
   }
   if (IfBlock2) {
-    for (auto &I : *IfBlock2)
+    for (auto &I : *IfBlock2) {
       I.dropUnknownNonDebugMetadata();
+      dropDebugUsers(I);
+    }
     DomBlock->getInstList().splice(InsertPt->getIterator(),
                                    IfBlock2->getInstList(), IfBlock2->begin(),
                                    IfBlock2->getTerminator()->getIterator());