[DebugInfo] Prefer to use setKillLocation rather than replacing operands with undef

[Orlando]

Summary

NFC-ish. There is a functional change but the outputs are semantically identical. Where we might've before replaced one operand with undef (which means "this is a kill location marker") the use of setKillLocation will replace all location operands with undef (which also means "this is a kill location marker").

Related to https://discourse.llvm.org/t/auto-undef-debug-uses-of-a-deleted-value

[StephenTozer]

Simple and good, LGTM.

llvm/test/DebugInfo/NVPTX/debug-info.ll

109 ↗

(On Diff #486006)

Meaningful, or just whitespace sneaking in?

[Orlando]

llvm/test/DebugInfo/NVPTX/debug-info.ll

109 ↗

(On Diff #486006)

Whoops, it snuck in and I forgot to change it back before committing. Worth fixing in post commit?

llvm/lib/Transforms/Utils/Local.cpp

while (!DeadInsts.empty()) {
 
     I->eraseFromParent();
   }
 }
 
 bool llvm::replaceDbgUsesWithUndef(Instruction *I) {
   SmallVector<DbgVariableIntrinsic *, 1> DbgUsers;
   findDbgUsers(DbgUsers, I);
-  for (auto *DII : DbgUsers) {
-    Value *Undef = UndefValue::get(I->getType());
-    DII->replaceVariableLocationOp(I, Undef);
-  }
+  for (auto *DII : DbgUsers)
+    DII->setKillLocation();
   return !DbgUsers.empty();
 }
 
 /// areAllUsesEqual - Check whether the uses of a value are all the same.
 /// This is similar to Instruction::hasOneUse() except this will also return
 /// true when there are no uses or multiple uses that all refer to the same
 /// value.
 static bool areAllUsesEqual(Instruction *I) {
if (AdditionalValues.empty() && IsValidSalvageExpr) {
                    MaxDebugArgs) {
       DII->addVariableLocationOps(AdditionalValues, SalvagedExpr);
     } else {
       // Do not salvage using DIArgList for dbg.addr/dbg.declare, as it is
       // currently only valid for stack value expressions. Do not salvage
       // using DIArgList for dbg.assign yet. FIXME: support this.
       // Also do not salvage if the resulting DIArgList would contain an
       // unreasonably large number of values.
-      Value *Undef = UndefValue::get(I.getOperand(0)->getType());
-      DII->replaceVariableLocationOp(I.getOperand(0), Undef);
+      DII->setKillLocation();
     }
     LLVM_DEBUG(dbgs() << "SALVAGE: " << *DII << '\n');
     Salvaged = true;
   }
 
   if (Salvaged)
     return;
 
-  for (auto *DII : DbgUsers) {
-    Value *Undef = UndefValue::get(I.getType());
-    DII->replaceVariableLocationOp(&I, Undef);
-  }
+  for (auto *DII : DbgUsers)
+    DII->setKillLocation();
 }
 
 Value *getSalvageOpsForGEP(GetElementPtrInst *GEP, const DataLayout &DL,
                            uint64_t CurrentLocOps,
                            SmallVectorImpl<uint64_t> &Opcodes,
                            SmallVectorImpl<Value *> &AdditionalValues) {
   unsigned BitWidth = DL.getIndexSizeInBits(GEP->getPointerAddressSpace());
   // Rewrite a GEP into a DIExpression.