[DebugInfo][X86] Fix handling of DBG_VALUE's in post-RA scheduler.

This patch fixes a bug with the updating of DBG_VALUE's in
BreakAntiDependencies. Previously, it would only attempt to update the first
DBG_VALUE following the instruction whose register is being changed,
potentially leaving DBG_VALUE's referring to the wrong register. Now the code
will update all DBG_VALUE's that immediately follow the instruction.

This issue was detected as a result of an optimized codegen difference with
"-g" where an X86 byte/word fixup was not performed due to a DBG_VALUE
referencing the wrong register.

Differential Revision: https://reviews.llvm.org/D31755

llvm-svn: 301309

3 files changed, 23 insertions, 8 deletions

diff --git a/llvm/lib/CodeGen/AggressiveAntiDepBreaker.cpp b/llvm/lib/CodeGen/AggressiveAntiDepBreaker.cpp
index 955524c2a67..3a57772cc7f 100644
--- a/llvm/lib/CodeGen/AggressiveAntiDepBreaker.cpp
+++ b/llvm/lib/CodeGen/AggressiveAntiDepBreaker.cpp
@@ -964,10 +964,8 @@ unsigned AggressiveAntiDepBreaker::BreakAntiDependencies(
               // sure to update that as well.
               const SUnit *SU = MISUnitMap[Q.second.Operand->getParent()];
               if (!SU) continue;
-              for (DbgValueVector::iterator DVI = DbgValues.begin(),
-                     DVE = DbgValues.end(); DVI != DVE; ++DVI)
-                if (DVI->second == Q.second.Operand->getParent())
-                  UpdateDbgValue(*DVI->first, AntiDepReg, NewReg);
+              UpdateDbgValues(DbgValues, Q.second.Operand->getParent(),
+                              AntiDepReg, NewReg);
             }
 
             // We just went back in time and modified history; the
diff --git a/llvm/lib/CodeGen/AntiDepBreaker.h b/llvm/lib/CodeGen/AntiDepBreaker.h
index 04f7f419f5e..d14d93100ad 100644
--- a/llvm/lib/CodeGen/AntiDepBreaker.h
+++ b/llvm/lib/CodeGen/AntiDepBreaker.h
@@ -60,6 +60,25 @@ public:
     if (MI.getOperand(0).isReg() && MI.getOperand(0).getReg() == OldReg)
       MI.getOperand(0).setReg(NewReg);
   }
+
+  /// Update all DBG_VALUE instructions that may be affected by the dependency
+  /// breaker's update of ParentMI to use NewReg.
+  void UpdateDbgValues(const DbgValueVector &DbgValues, MachineInstr *ParentMI,
+                       unsigned OldReg, unsigned NewReg) {
+    // The following code is dependent on the order in which the DbgValues are
+    // constructed in ScheduleDAGInstrs::buildSchedGraph.
+    MachineInstr *PrevDbgMI = nullptr;
+    for (const auto &DV : make_range(DbgValues.crbegin(), DbgValues.crend())) {
+      MachineInstr *PrevMI = DV.second;
+      if ((PrevMI == ParentMI) || (PrevMI == PrevDbgMI)) {
+        MachineInstr *DbgMI = DV.first;
+        UpdateDbgValue(*DbgMI, OldReg, NewReg);
+        PrevDbgMI = DbgMI;
+      } else if (PrevDbgMI) {
+        break; // If no match and already found a DBG_VALUE, we're done.
+      }
+    }
+  }
 };
 
 }
diff --git a/llvm/lib/CodeGen/CriticalAntiDepBreaker.cpp b/llvm/lib/CodeGen/CriticalAntiDepBreaker.cpp
index e1eeddf0816..b2d6652b075 100644
--- a/llvm/lib/CodeGen/CriticalAntiDepBreaker.cpp
+++ b/llvm/lib/CodeGen/CriticalAntiDepBreaker.cpp
@@ -648,10 +648,8 @@ BreakAntiDependencies(const std::vector<SUnit>& SUnits,
           // as well.
           const SUnit *SU = MISUnitMap[Q->second->getParent()];
           if (!SU) continue;
-          for (DbgValueVector::iterator DVI = DbgValues.begin(),
-                 DVE = DbgValues.end(); DVI != DVE; ++DVI)
-            if (DVI->second == Q->second->getParent())
-              UpdateDbgValue(*DVI->first, AntiDepReg, NewReg);
+          UpdateDbgValues(DbgValues, Q->second->getParent(),
+                          AntiDepReg, NewReg);
         }
 
         // We just went back in time and modified history; the