Alternative solution to soliving the entry_value issue.

Treat entry_values as constants, they will be treated just as a
DBG_VALUE 1, $noreg, !1, DIExpression(), debug-location !2

Author: rastogishubham

llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp

@@ -668,16 +668,6 @@ class TransferTracker {
 
     auto &[Var, DILoc] = DVMap.lookupDVID(VarID);
 
-    // If the expression is a DW_OP_entry_value, emit the variable location
-    // as-is.
-    if (DIExpr->isEntryValue()) {
-      Register Reg = MTracker->LocIdxToLocID[Num.getLoc()];
-      MachineOperand MO = MachineOperand::CreateReg(Reg, false);
-      PendingDbgValues.push_back(std::make_pair(
-          VarID, &*emitMOLoc(MO, Var, {DIExpr, Prop.Indirect, false})));
-      return true;
-    }
-
     // Is the variable appropriate for entry values (i.e., is a parameter).
     if (!isEntryValueVariable(Var, DIExpr))
       return false;
@@ -1458,7 +1448,10 @@ bool InstrRefBasedLDV::transferDebugValue(const MachineInstr &MI) {
       for (const MachineOperand &MO : MI.debug_operands()) {
         // There should be no undef registers here, as we've screened for undef
         // debug values.
-        if (MO.isReg()) {
+        if (MI.getDebugExpression()->isEntryValue()) {
+          // If the DBG_VALUE is a DW_OP_entry_value, treat it as a constant.
+          DebugOps.push_back(DbgOpStore.insert(MO));
+        } else if (MO.isReg()) {
           DebugOps.push_back(DbgOpStore.insert(MTracker->readReg(MO.getReg())));
         } else if (MO.isImm() || MO.isFPImm() || MO.isCImm()) {
           DebugOps.push_back(DbgOpStore.insert(MO));

llvm/test/DebugInfo/MIR/InstrRef/entry_value_clobbered_stack_copy.mir

@@ -1,6 +1,9 @@
 # RUN: llc --run-pass=livedebugvalues -o - %s | FileCheck %s
 # REQUIRES: x86-registered-target
 
+# This test covers the scenario where a DBG_VALUE created prior to LiveDebugValues has an entry-value expression. 
+# It tests that an EntryValue DBG_VALUE is propagated in a diamond-shaped CFG.
+
 --- |
   target triple = "x86_64-"
   define void @foo(ptr swiftasync %0) !dbg !4 {
@@ -47,4 +50,4 @@ body:             |
 # CHECK: bb.0:
 # CHECK:      MOV64mr $rbp, 1, $noreg, -48, $noreg, $r14
 # CHECK-NEXT: DBG_VALUE $r14, {{.*}}, !DIExpression(DW_OP_LLVM_entry_value, 1)
-# CHECK-NOT:  DBG_VALUE
+# CHECK-NOT:  DBG_VALUE

llvm/test/DebugInfo/MIR/InstrRef/entry_value_gets_propagated.mir

@@ -1,5 +1,9 @@
-# RUN: llc --run-pass=livedebugvalues -o - %s | FileCheck %s
+# RUN: llc --run-pass=livedebugvalues -o - %s | FileCheck %s --implicit-check-not=DBG_VALUE 
 # REQUIRES: x86-registered-target
+
+# This test covers the scenario where a DBG_VALUE created prior to LiveDebugValues has an entry-value expression.
+# It ensures that a clobbered stack copy doesn't crash if used as an entry-value because entry-values can't be clobbered.
+
 --- |
   target triple = "x86_64-"
 
@@ -64,13 +68,13 @@ body:             |
     successors: %bb.2(0x40000000), %bb.1(0x40000000)
     liveins: $r14, $edi, $edx, $esi
     DBG_VALUE $r14, $noreg, !14, !DIExpression(DW_OP_LLVM_entry_value, 1), debug-location !19
-    $r14 = MOV64ri 0, debug-location !20
     CMP32ri killed renamable $edx, 0, implicit-def $eflags, debug-location !20
     JCC_1 %bb.2, 4, implicit killed $eflags, debug-location !22
   bb.1.if.then:
     successors: %bb.3(0x80000000)
     liveins: $edi, $r13
     CALL64pcrel32 @foo, csr_64, implicit $rsp, implicit $ssp, implicit $edi, implicit-def $eax, debug-location !23
+    $r14 = MOV64ri 0, debug-location !20
     JMP_1 %bb.3, debug-location !25
   bb.2.if.else:
     successors: %bb.3(0x80000000)
@@ -85,7 +89,10 @@ body:             |
 # CHECK: DBG_VALUE $r14, {{.*}}, !DIExpression(DW_OP_LLVM_entry_value, 1)
 # CHECK-LABEL: bb.1.if.then:
 # CHECK: DBG_VALUE $r14, {{.*}}, !DIExpression(DW_OP_LLVM_entry_value, 1)
+# CHECK-NEXT: CALL64pcrel32 @foo
+# CHECK-NEXT: $r14 = MOV64ri 0
+# CHECK-NOT: DBG_VALUE $r14, {{.*}}, !DIExpression(DW_OP_LLVM_entry_value, 1)
 # CHECK-LABEL: bb.2.if.else:
 # CHECK: DBG_VALUE $r14, {{.*}}, !DIExpression(DW_OP_LLVM_entry_value, 1)
 # CHECK-LABEL: bb.3.if.end:
-# CHECK: DBG_VALUE $r14, {{.*}}, !DIExpression(DW_OP_LLVM_entry_value, 1)
+# CHECK: DBG_VALUE $r14, {{.*}}, !DIExpression(DW_OP_LLVM_entry_value, 1)