Fix out-of-order stepping behavior in programs with sunk instructions.

MachineSink attempts to place instructions near the basic blocks where
they are needed.  Once an instruction has been sunk, its location
relative to other instructions no longer is consistent with the
original source code. In order to ensure correct stepping in the
debugger, the debug location for sunk instructions is either merged
with the insertion point or erased if the target successor block is
empty.

Originally submitted as r318679, revised to fix sanitizer failure and
improve testing.

Patch by Matthew Voss!

Differential Revision: https://reviews.llvm.org/D39933

llvm-svn: 320216

1 files changed, 11 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/MachineSink.cpp b/llvm/lib/CodeGen/MachineSink.cpp
index f932df71cdb..fd4bd1a588c 100644
--- a/llvm/lib/CodeGen/MachineSink.cpp
+++ b/llvm/lib/CodeGen/MachineSink.cpp
@@ -38,6 +38,7 @@
 #include "llvm/CodeGen/TargetSubtargetInfo.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/BranchProbability.h"
 #include "llvm/Support/CommandLine.h"
@@ -868,11 +869,20 @@ bool MachineSinking::SinkInstruction(MachineInstr &MI, bool &SawStore,
   SmallVector<MachineInstr *, 2> DbgValuesToSink;
   collectDebugValues(MI, DbgValuesToSink);
 
+  // Merge or erase debug location to ensure consistent stepping in profilers
+  // and debuggers.
+  if (!SuccToSinkTo->empty() && InsertPos != SuccToSinkTo->end())
+    MI.setDebugLoc(DILocation::getMergedLocation(MI.getDebugLoc(),
+                                                 InsertPos->getDebugLoc()));
+  else
+    MI.setDebugLoc(DebugLoc());
+
+
   // Move the instruction.
   SuccToSinkTo->splice(InsertPos, ParentBlock, MI,
                        ++MachineBasicBlock::iterator(MI));
 
-  // Move debug values.
+  // Move previously adjacent debug value instructions to the insert position.
   for (SmallVectorImpl<MachineInstr *>::iterator DBI = DbgValuesToSink.begin(),
          DBE = DbgValuesToSink.end(); DBI != DBE; ++DBI) {
     MachineInstr *DbgMI = *DBI;