[LiveDebugValues] Remove swift customizations introducing entry values

With the new approach to entry values, codegen no longer needs to get involved,
so these LDV customizations are no longer needed.

These were particularly problematic as they were re-introducing entry values in
the "entry funclet" of certain swift async functions.

(cherry picked from commit 56252e3)

Author: felipepiovezan

llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp

@@ -1420,7 +1420,6 @@ bool InstrRefBasedLDV::transferDebugValue(const MachineInstr &MI) {
 
   // MLocTracker needs to know that this register is read, even if it's only
   // read by a debug inst.
-  bool convertToSwiftAsyncEntryValue = false;
   for (const MachineOperand &MO : MI.debug_operands())
     if (MO.isReg() && MO.getReg() != 0) {
       ValueIDNum RegId = MTracker->readReg(MO.getReg());
@@ -1438,17 +1437,9 @@ bool InstrRefBasedLDV::transferDebugValue(const MachineInstr &MI) {
         if (!Expr || !Expr->isEntryValue()) {
           if (TTracker)
             TTracker->recoverAsEntryValue(V, Properties, RegId);
-          else
-            convertToSwiftAsyncEntryValue = true;
         }
       }
     }
-
-  if (convertToSwiftAsyncEntryValue && Expr && !MI.isDebugValueList()) {
-    const_cast<MachineInstr *>(&MI)->getOperand(3).setMetadata(
-        DIExpression::prepend(Expr, DIExpression::EntryValue));
-    Properties.DIExpr = MI.getDebugExpression();
-  }
   // END SWIFT
 
   // If we're preparing for the second analysis (variables), the machine value

llvm/lib/CodeGen/LiveDebugValues/VarLocBasedImpl.cpp

@@ -2293,40 +2293,11 @@ bool VarLocBasedLDV::ExtendRanges(MachineFunction &MF,
 
   // Only in the case of entry MBB collect DBG_VALUEs representing
   // function parameters in order to generate debug entry values for them.
-  SmallVector<MachineInstr *, 8> AsyncDbgValues;
   MachineBasicBlock &First_MBB = *(MF.begin());
-  // Use a cache so that we only hoist the first swift async context debug inst
-  // for a specific DBG_VALUE. Otherwise, we may hoist inappropriately over a
-  // llvm.dbg.value.
-  SmallDenseSet<DebugVariable, 8> SeenDebugVars;
   for (auto &MI : First_MBB) {
     collectRegDefs(MI, DefinedRegs, TRI);
-    if (MI.isDebugValue()) {
-      // In Swift async functions entry values are preferred, since they
-      // can be evaluated in both live frames and virtual backtraces.
-      if (SeenDebugVars
-              .insert(DebugVariable(MI.getDebugVariable(),
-                                    MI.getDebugExpression(),
-                                    MI.getDebugLoc()->getInlinedAt()))
-              .second &&
-          isSwiftAsyncContext(MI) && !MI.isDebugValueList()) {
-        // If our instruction is not an entry value yet, make it an entry value.
-        if (!MI.getDebugExpression()->isEntryValue()) {
-          MI.getOperand(3).setMetadata(DIExpression::prepend(
-              MI.getDebugExpression(), DIExpression::EntryValue));
-        }
-        AsyncDbgValues.push_back(&MI);
-      } else {
-        recordEntryValue(MI, DefinedRegs, OpenRanges, VarLocIDs);
-      }
-    }
-  }
-
-  if (AsyncDbgValues.size()) {
-    // Make sure the async entry values are at the very start.
-    auto InsertPt = First_MBB.getFirstNonDebugInstr();
-    for (auto *MI : llvm::reverse(AsyncDbgValues))
-      MI->moveBefore(&*InsertPt);
+    if (MI.isDebugValue())
+      recordEntryValue(MI, DefinedRegs, OpenRanges, VarLocIDs);
   }
 
   // Initialize per-block structures and scan for fragment overlaps.