When instructions are hoisted out of loops by MachineLICM, remove their debug loc.

This prevents erratic stepping behavior as well as incorrect source attribution
for sample profiling.

Reviewers: dblakie

Subscribers: llvm-commit

Differential Revision: https://reviews.llvm.org/D27290

llvm-svn: 288442

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/MachineLICM.cpp b/llvm/lib/CodeGen/MachineLICM.cpp
index e2d00d0e6f5..b3d18435985 100644
--- a/llvm/lib/CodeGen/MachineLICM.cpp
+++ b/llvm/lib/CodeGen/MachineLICM.cpp
@@ -1336,6 +1336,11 @@ bool MachineLICM::Hoist(MachineInstr *MI, MachineBasicBlock *Preheader) {
     // Otherwise, splice the instruction to the preheader.
     Preheader->splice(Preheader->getFirstTerminator(),MI->getParent(),MI);
 
+    // Since we are moving the instruction out of its basic block, we do not
+    // retain its debug location. Doing so would degrade the debugging 
+    // experience and adversely affect the accuracy of profiling information.
+    MI->setDebugLoc(DebugLoc());
+
     // Update register pressure for BBs from header to this block.
     UpdateBackTraceRegPressure(MI);