[DebugInfo] Handle multiple variable location operands in IR

This patch updates the various IR passes to correctly handle dbg.values with a
DIArgList location. This patch does not actually allow DIArgLists to be produced
by salvageDebugInfo, and it does not affect any pass after codegen-prepare.
Other than that, it should cover every IR pass.

Most of the changes simply extend code that operated on a single debug value to
operate on the list of debug values in the style of any_of, all_of, for_each,
etc. Instances of setOperand(0, ...) have been replaced with with
replaceVariableLocationOp, which takes the value that is being replaced as an
additional argument. In places where this value isn't readily available, we have
to track the old value through to the point where it gets replaced.

Differential Revision: https://reviews.llvm.org/D88232

1 files changed, 63 insertions, 34 deletions

diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index e745a37..7c97756 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -2855,11 +2855,16 @@ class TypePromotionTransaction {
     /// Keep track of the debug users.
     SmallVector<DbgValueInst *, 1> DbgValues;
 
+    /// Keep track of the new value so that we can undo it by replacing
+    /// instances of the new value with the original value.
+    Value *New;
+
     using use_iterator = SmallVectorImpl<InstructionAndIdx>::iterator;
 
   public:
     /// Replace all the use of \p Inst by \p New.
-    UsesReplacer(Instruction *Inst, Value *New) : TypePromotionAction(Inst) {
+    UsesReplacer(Instruction *Inst, Value *New)
+        : TypePromotionAction(Inst), New(New) {
       LLVM_DEBUG(dbgs() << "Do: UsersReplacer: " << *Inst << " with " << *New
                         << "\n");
       // Record the original uses.
@@ -2885,7 +2890,7 @@ class TypePromotionTransaction {
       // the original debug uses must also be reinstated to maintain the
       // correctness and utility of debug value instructions.
       for (auto *DVI : DbgValues)
-        DVI->replaceVariableLocationOp(DVI->getVariableLocationOp(0), Inst);
+        DVI->replaceVariableLocationOp(New, Inst);
     }
   };
 
@@ -7876,18 +7881,21 @@ bool CodeGenPrepare::fixupDbgValue(Instruction *I) {
   DbgValueInst &DVI = *cast<DbgValueInst>(I);
 
   // Does this dbg.value refer to a sunk address calculation?
-  Value *Location = DVI.getVariableLocationOp(0);
-  WeakTrackingVH SunkAddrVH = SunkAddrs[Location];
-  Value *SunkAddr = SunkAddrVH.pointsToAliveValue() ? SunkAddrVH : nullptr;
-  if (SunkAddr) {
-    // Point dbg.value at locally computed address, which should give the best
-    // opportunity to be accurately lowered. This update may change the type of
-    // pointer being referred to; however this makes no difference to debugging
-    // information, and we can't generate bitcasts that may affect codegen.
-    DVI.replaceVariableLocationOp(Location, SunkAddr);
-    return true;
-  }
-  return false;
+  bool AnyChange = false;
+  for (Value *Location : DVI.getValues()) {
+    WeakTrackingVH SunkAddrVH = SunkAddrs[Location];
+    Value *SunkAddr = SunkAddrVH.pointsToAliveValue() ? SunkAddrVH : nullptr;
+    if (SunkAddr) {
+      // Point dbg.value at locally computed address, which should give the best
+      // opportunity to be accurately lowered. This update may change the type
+      // of pointer being referred to; however this makes no difference to
+      // debugging information, and we can't generate bitcasts that may affect
+      // codegen.
+      DVI.replaceVariableLocationOp(Location, SunkAddr);
+      AnyChange = true;
+    }
+  }
+  return AnyChange;
 }
 
 // A llvm.dbg.value may be using a value before its definition, due to
@@ -7906,30 +7914,51 @@ bool CodeGenPrepare::placeDbgValues(Function &F) {
       if (!DVI)
         continue;
 
-      Instruction *VI = dyn_cast_or_null<Instruction>(DVI->getValue());
+      SmallVector<Instruction *, 4> VIs;
+      for (Value *V : DVI->getValues())
+        if (Instruction *VI = dyn_cast_or_null<Instruction>(V))
+          VIs.push_back(VI);
+
+      // This DVI may depend on multiple instructions, complicating any
+      // potential sink. This block takes the defensive approach, opting to
+      // "undef" the DVI if it has more than one instruction and any of them do
+      // not dominate DVI.
+      for (Instruction *VI : VIs) {
+        if (VI->isTerminator())
+          continue;
 
-      if (!VI || VI->isTerminator())
-        continue;
+        // If VI is a phi in a block with an EHPad terminator, we can't insert
+        // after it.
+        if (isa<PHINode>(VI) && VI->getParent()->getTerminator()->isEHPad())
+          continue;
 
-      // If VI is a phi in a block with an EHPad terminator, we can't insert
-      // after it.
-      if (isa<PHINode>(VI) && VI->getParent()->getTerminator()->isEHPad())
-        continue;
+        // If the defining instruction dominates the dbg.value, we do not need
+        // to move the dbg.value.
+        if (DT.dominates(VI, DVI))
+          continue;
 
-      // If the defining instruction dominates the dbg.value, we do not need
-      // to move the dbg.value.
-      if (DT.dominates(VI, DVI))
-        continue;
+        // If we depend on multiple instructions and any of them doesn't
+        // dominate this DVI, we probably can't salvage it: moving it to
+        // after any of the instructions could cause us to lose the others.
+        if (VIs.size() > 1) {
+          LLVM_DEBUG(
+              dbgs()
+              << "Unable to find valid location for Debug Value, undefing:\n"
+              << *DVI);
+          DVI->setUndef();
+          break;
+        }
 
-      LLVM_DEBUG(dbgs() << "Moving Debug Value before :\n"
-                        << *DVI << ' ' << *VI);
-      DVI->removeFromParent();
-      if (isa<PHINode>(VI))
-        DVI->insertBefore(&*VI->getParent()->getFirstInsertionPt());
-      else
-        DVI->insertAfter(VI);
-      MadeChange = true;
-      ++NumDbgValueMoved;
+        LLVM_DEBUG(dbgs() << "Moving Debug Value before :\n"
+                          << *DVI << ' ' << *VI);
+        DVI->removeFromParent();
+        if (isa<PHINode>(VI))
+          DVI->insertBefore(&*VI->getParent()->getFirstInsertionPt());
+        else
+          DVI->insertAfter(VI);
+        MadeChange = true;
+        ++NumDbgValueMoved;
+      }
     }
   }
   return MadeChange;