[Transforms] Avoid repeated hash lookups (NFC) (#131556)

Author: kazutakahirata

llvm/lib/Transforms/Utils/BasicBlockUtils.cpp

@@ -511,7 +511,7 @@ DbgVariableRecordsRemoveRedundantDbgInstrsUsingForwardScan(BasicBlock *BB) {
         continue;
       DebugVariable Key(DVR.getVariable(), std::nullopt,
                         DVR.getDebugLoc()->getInlinedAt());
-      auto VMI = VariableMap.find(Key);
+      auto [VMI, Inserted] = VariableMap.try_emplace(Key);
       // A dbg.assign with no linked instructions can be treated like a
       // dbg.value (i.e. can be deleted).
       bool IsDbgValueKind =
@@ -520,12 +520,12 @@ DbgVariableRecordsRemoveRedundantDbgInstrsUsingForwardScan(BasicBlock *BB) {
       // Update the map if we found a new value/expression describing the
       // variable, or if the variable wasn't mapped already.
       SmallVector<Value *, 4> Values(DVR.location_ops());
-      if (VMI == VariableMap.end() || VMI->second.first != Values ||
+      if (Inserted || VMI->second.first != Values ||
           VMI->second.second != DVR.getExpression()) {
         if (IsDbgValueKind)
-          VariableMap[Key] = {Values, DVR.getExpression()};
+          VMI->second = {Values, DVR.getExpression()};
         else
-          VariableMap[Key] = {Values, nullptr};
+          VMI->second = {Values, nullptr};
         continue;
       }
       // Don't delete dbg.assign intrinsics that are linked to instructions.
@@ -591,7 +591,7 @@ static bool removeRedundantDbgInstrsUsingForwardScan(BasicBlock *BB) {
     if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(&I)) {
       DebugVariable Key(DVI->getVariable(), std::nullopt,
                         DVI->getDebugLoc()->getInlinedAt());
-      auto VMI = VariableMap.find(Key);
+      auto [VMI, Inserted] = VariableMap.try_emplace(Key);
       auto *DAI = dyn_cast<DbgAssignIntrinsic>(DVI);
       // A dbg.assign with no linked instructions can be treated like a
       // dbg.value (i.e. can be deleted).
@@ -600,15 +600,15 @@ static bool removeRedundantDbgInstrsUsingForwardScan(BasicBlock *BB) {
       // Update the map if we found a new value/expression describing the
       // variable, or if the variable wasn't mapped already.
       SmallVector<Value *, 4> Values(DVI->getValues());
-      if (VMI == VariableMap.end() || VMI->second.first != Values ||
+      if (Inserted || VMI->second.first != Values ||
           VMI->second.second != DVI->getExpression()) {
         // Use a sentinel value (nullptr) for the DIExpression when we see a
         // linked dbg.assign so that the next debug intrinsic will never match
         // it (i.e. always treat linked dbg.assigns as if they're unique).
         if (IsDbgValueKind)
-          VariableMap[Key] = {Values, DVI->getExpression()};
+          VMI->second = {Values, DVI->getExpression()};
         else
-          VariableMap[Key] = {Values, nullptr};
+          VMI->second = {Values, nullptr};
         continue;
       }