Index: llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
===================================================================
--- llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
+++ llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
@@ -132,9 +132,9 @@
     // unecessary function-local metadata. Remember that we've seen a
     // dbg.assign for each variable fragment for the untracked store handling
     // (after this loop).
-    SmallSet<DebugVariable, 2> VarHasDbgAssignForStore;
+    SmallSet<DebugVariableAggregate, 2> VarHasDbgAssignForStore;
     for (DbgAssignIntrinsic *DAI : at::getAssignmentMarkers(ToDelete)) {
-      VarHasDbgAssignForStore.insert(DebugVariable(DAI));
+      VarHasDbgAssignForStore.insert(DebugVariableAggregate(DAI));
       DbgAssignsToDelete->insert(DAI);
       DIB.insertDbgValueIntrinsic(DAI->getValue(), DAI->getVariable(),
                                   DAI->getExpression(), DAI->getDebugLoc(),
@@ -150,7 +150,7 @@
     // size) or one that is trackable but has had its DIAssignID attachment
     // dropped accidentally.
     for (auto *DAI : DbgAssigns) {
-      if (VarHasDbgAssignForStore.contains(DebugVariable(DAI)))
+      if (VarHasDbgAssignForStore.contains(DebugVariableAggregate(DAI)))
         continue;
       ConvertDebugDeclareToDebugValue(DAI, ToDelete, DIB);
     }
Index: llvm/test/DebugInfo/Generic/assignment-tracking/mem2reg/store-to-part-of-alloca.ll
===================================================================
--- /dev/null
+++ llvm/test/DebugInfo/Generic/assignment-tracking/mem2reg/store-to-part-of-alloca.ll
@@ -0,0 +1,84 @@
+; RUN: opt -passes=mem2reg -S %s -o - | FileCheck %s --implicit-check-not="call void @llvm.dbg"
+
+; CHECK: llvm.dbg.value(metadata i64 0, metadata ![[#]], metadata !DIExpression(DW_OP_LLVM_fragment, 0, 32))
+
+;; The store has a debug intrinsic attached to it with a fragment size
+;; different to the base alloca debug intrinsic fragment size. Check that
+;; mem2reg doesn't think this store is "untagged" for that base variable.  If
+;; that were the case mem2reg would insert a dbg.value covering the entire
+;; variable, which isn't the right thing to do here. This example looks weird
+;; and not particularly compelling, but this was encountered in the wild on
+;; "real code".
+
+;; Reduced from this C++ (which itself has been reduced).
+;; class a {
+;; public:
+;;   a(float, float);
+;; };
+;; class d {
+;; protected:
+;;   float b[4];
+;; 
+;; public:
+;;   float e() { return b[0]; }
+;;   float f() { return b[1]; }
+;; };
+;; class g : public d {
+;; public:
+;;   void operator*=(g) {
+;;     {
+;;       float __attribute__((nodebug)) c = b[2], __attribute__((nodebug)) h = b[0];
+;;       b[0] = c;
+;;       b[1] = h;
+;;     }
+;;   }
+;; };
+;; g get();
+;; void i() {
+;;   g __attribute__((nodebug)) j = get();
+;;   g k = j;
+;;   k *= j;
+;;   a(k.e(), k.f());
+;; }
+
+define dso_local i64 @_Z3funv() #0 !dbg !10 {
+entry:
+  %retval.sroa.0 = alloca i64, align 8, !DIAssignID !20
+  call void @llvm.dbg.assign(metadata i1 undef, metadata !19, metadata !DIExpression(), metadata !20, metadata ptr %retval.sroa.0, metadata !DIExpression()), !dbg !21
+  store i64 0, ptr %retval.sroa.0, align 8, !dbg !22, !DIAssignID !23
+  call void @llvm.dbg.assign(metadata i64 0, metadata !19, metadata !DIExpression(DW_OP_LLVM_fragment, 0, 32), metadata !23, metadata ptr %retval.sroa.0, metadata !DIExpression()), !dbg !21
+  ret i64 0
+}
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
+declare void @llvm.dbg.assign(metadata, metadata, metadata, metadata, metadata, metadata) #1
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5, !6, !7, !8}
+!llvm.ident = !{!9}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 17.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test.cpp", directory: "/")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{i32 8, !"PIC Level", i32 2}
+!6 = !{i32 7, !"PIE Level", i32 2}
+!7 = !{i32 7, !"uwtable", i32 2}
+!8 = !{i32 7, !"debug-info-assignment-tracking", i1 true}
+!9 = !{!"clang version 17.0.0"}
+!10 = distinct !DISubprogram(name: "fun", linkageName: "_Z3funv", scope: !1, file: !1, line: 2, type: !11, scopeLine: 2, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !18)
+!11 = !DISubroutineType(types: !12)
+!12 = !{!13}
+!13 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "Pair", file: !1, line: 1, size: 64, flags: DIFlagTypePassByValue, elements: !14, identifier: "_ZTS4Pair")
+!14 = !{!15, !17}
+!15 = !DIDerivedType(tag: DW_TAG_member, name: "A", scope: !13, file: !1, line: 1, baseType: !16, size: 32)
+!16 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!17 = !DIDerivedType(tag: DW_TAG_member, name: "B", scope: !13, file: !1, line: 1, baseType: !16, size: 32, offset: 32)
+!18 = !{!19}
+!19 = !DILocalVariable(name: "X", scope: !10, file: !1, line: 3, type: !13)
+!20 = distinct !DIAssignID()
+!21 = !DILocation(line: 0, scope: !10)
+!22 = !DILocation(line: 3, column: 8, scope: !10)
+!23 = distinct !DIAssignID()
+!24 = !DILocation(line: 4, column: 3, scope: !10)
Index: llvm/test/DebugInfo/Generic/assignment-tracking/sroa/vec-2.ll
===================================================================
--- llvm/test/DebugInfo/Generic/assignment-tracking/sroa/vec-2.ll
+++ llvm/test/DebugInfo/Generic/assignment-tracking/sroa/vec-2.ll
@@ -30,7 +30,6 @@
 ;; There's a few dbg intrinsics we're not interested in testing wedged in here.
 ; CHECK-NEXT: dbg.value
 ; CHECK-NEXT: dbg.value
-; CHECK-NEXT: dbg.value
 ; CHECK-NEXT: call void @llvm.dbg.value(metadata float %2,{{.+}}, metadata !DIExpression(DW_OP_LLVM_fragment, 96, 32))
 
 %class.d = type { %class.a }