When GVN removes a redundant load, it should not modify the debug location of the dominating load.

In the case of a fully redundant load LI dominated by an equivalent load V, GVN
should always preserve the original debug location of V. Otherwise, we risk to
introduce an incorrect stepping.
If V has debug info, then clearly it should not be modified. If V has a null
debugloc, then it is still potentially incorrect to propagate LI's debugloc
because LI may not post-dominate V.

Differential Revision: https://reviews.llvm.org/D27468

llvm-svn: 288903

1 files changed, 4 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/GVN.cpp b/llvm/lib/Transforms/Scalar/GVN.cpp
index 81f273ff318..9485bfd7c29 100644
--- a/llvm/lib/Transforms/Scalar/GVN.cpp
+++ b/llvm/lib/Transforms/Scalar/GVN.cpp
@@ -1700,7 +1700,10 @@ bool GVN::processNonLocalLoad(LoadInst *LI) {
     if (isa<PHINode>(V))
       V->takeName(LI);
     if (Instruction *I = dyn_cast<Instruction>(V))
-      if (LI->getDebugLoc())
+      // If instruction I has debug info, then we should not update it.
+      // Also, if I has a null DebugLoc, then it is still potentially incorrect
+      // to propagate LI's DebugLoc because LI may not post-dominate I.
+      if (LI->getDebugLoc() && ValuesPerBlock.size() != 1)
         I->setDebugLoc(LI->getDebugLoc());
     if (V->getType()->getScalarType()->isPointerTy())
       MD->invalidateCachedPointerInfo(V);