Remove debug info when hoisting instruction from then/else branch.

Summary: The hoisted instruction is executed speculatively. It could affect the debugging experience as user would see gdb go into code that may not be expected to execute. It will also affect sample profile accuracy by assigning incorrect frequency to source within then/else branch.

Reviewers: davidxl, dblaikie, chandlerc, kcc, echristo

Subscribers: mehdi_amini, probinson, eric_niebler, andreadb, llvm-commits

Differential Revision: https://reviews.llvm.org/D24164

llvm-svn: 280995

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 1d5d853..921f325 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1242,6 +1242,14 @@ static bool HoistThenElseCodeToIf(BranchInst *BI,
                            LLVMContext::MD_dereferenceable_or_null,
                            LLVMContext::MD_mem_parallel_loop_access};
     combineMetadata(I1, I2, KnownIDs);
+
+    // If the debug loc for I1 and I2 are different, as we are combining them
+    // into one instruction, we do not want to select debug loc randomly from 
+    // I1 or I2. Instead, we set the 0-line DebugLoc to note that we do not
+    // know the debug loc of the hoisted instruction.
+    if (!isa<CallInst>(I1) &&  I1->getDebugLoc() != I2->getDebugLoc())
+      I1->setDebugLoc(DebugLoc());
+ 
     I2->eraseFromParent();
     Changed = true;