diff --git a/llvm/lib/CodeGen/TargetInstrInfo.cpp b/llvm/lib/CodeGen/TargetInstrInfo.cpp
--- a/llvm/lib/CodeGen/TargetInstrInfo.cpp
+++ b/llvm/lib/CodeGen/TargetInstrInfo.cpp
@@ -1130,9 +1130,6 @@
   if (isCopyInstr(MI, SrcRegOp, DestRegOp)) {
     Op = SrcRegOp;
     return ParamLoadedValue(*Op, Expr);
-  } else if (MI.isMoveImmediate()) {
-    Op = &MI.getOperand(1);
-    return ParamLoadedValue(*Op, Expr);
   }
 
   return None;
diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp
--- a/llvm/lib/Target/X86/X86InstrInfo.cpp
+++ b/llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -7638,12 +7638,17 @@
 
     return ParamLoadedValue(*Op, Expr);;
   }
+  case X86::MOV32ri:
+  case X86::MOV64ri:
+  case X86::MOV64ri32:
+    return ParamLoadedValue(MI.getOperand(1), Expr);
   case X86::XOR32rr: {
     if (MI.getOperand(1).getReg() == MI.getOperand(2).getReg())
       return ParamLoadedValue(MachineOperand::CreateImm(0), Expr);
     return None;
   }
   default:
+    assert(!MI.isMoveImmediate() && "Unexpected MoveImm instruction");
     return TargetInstrInfo::describeLoadedValue(MI);
   }
 }
diff --git a/llvm/test/DebugInfo/MIR/SystemZ/call-site-lzer.mir b/llvm/test/DebugInfo/MIR/SystemZ/call-site-lzer.mir
new file mode 100644
--- /dev/null
+++ b/llvm/test/DebugInfo/MIR/SystemZ/call-site-lzer.mir
@@ -0,0 +1,83 @@
+# RUN: llc -debug-entry-values -start-after=livedebugvalues -o - %s | FileCheck %s
+
+# This test would previously trigger an assertion when trying to describe the
+# call site value for callee()'s float parameter.
+#
+# Please note that at the time of creating this test the SystemZ target did not
+# support call site information, so the "callSites" array has been manually
+# added. For now, verify that we don't crash, and that no (invalid) call site
+# parameter entry is emitted, but later on when call site information is added
+# to the target the LZER instruction should be properly described.
+
+# CHECK-NOT: DW_TAG_GNU_call_site_parameter
+
+# Based on the following C reproducer:
+#
+# extern void callee(float);
+# int caller() {
+#   callee(0);
+#   return 0;
+# }
+
+--- |
+  target datalayout = "E-m:e-i1:8:16-i8:8:16-i64:64-f128:64-a:8:16-n32:64"
+  target triple = "systemz"
+
+  ; Function Attrs: nounwind
+  define signext i32 @caller() !dbg !12 {
+  entry:
+    tail call void @callee(float 0.000000e+00), !dbg !16
+    ret i32 0, !dbg !17
+  }
+
+  declare !dbg !4 void @callee(float)
+
+  !llvm.dbg.cu = !{!0}
+  !llvm.module.flags = !{!8, !9, !10}
+  !llvm.ident = !{!11}
+
+  !0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 10.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !3, nameTableKind: None)
+  !1 = !DIFile(filename: "systemz-lzer.c", directory: "/")
+  !2 = !{}
+  !3 = !{!4}
+  !4 = !DISubprogram(name: "callee", scope: !1, file: !1, line: 1, type: !5, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !2)
+  !5 = !DISubroutineType(types: !6)
+  !6 = !{null, !7}
+  !7 = !DIBasicType(name: "float", size: 32, encoding: DW_ATE_float)
+  !8 = !{i32 2, !"Dwarf Version", i32 4}
+  !9 = !{i32 2, !"Debug Info Version", i32 3}
+  !10 = !{i32 1, !"wchar_size", i32 4}
+  !11 = !{!"clang version 10.0.0"}
+  !12 = distinct !DISubprogram(name: "caller", scope: !1, file: !1, line: 2, type: !13, scopeLine: 2, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+  !13 = !DISubroutineType(types: !14)
+  !14 = !{!15}
+  !15 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+  !16 = !DILocation(line: 3, scope: !12)
+  !17 = !DILocation(line: 4, scope: !12)
+
+...
+---
+name:            caller
+tracksRegLiveness: true
+callSites:
+  - { bb: 0, offset: 9, fwdArgRegs:
+      - { arg: 0, reg: '$f0s' } }
+body:             |
+  bb.0.entry:
+    liveins: $r11d, $r15d, $r14d
+
+    STMG killed $r11d, killed $r15d, $r15d, 88, implicit killed $r14d
+    CFI_INSTRUCTION offset $r11d, -72
+    CFI_INSTRUCTION offset $r14d, -48
+    CFI_INSTRUCTION offset $r15d, -40
+    $r15d = AGHI $r15d, -160, implicit-def dead $cc
+    CFI_INSTRUCTION def_cfa_offset 320
+    $r11d = LGR $r15d
+    CFI_INSTRUCTION def_cfa_register $r11d
+    renamable $f0s = LZER
+    CallBRASL @callee, $f0s, csr_systemz, implicit-def dead $r14d, implicit-def dead $cc, implicit $fpc, debug-location !16
+    $r2d = LGHI 0, debug-location !17
+    $r11d, $r15d = LMG $r11d, 248, implicit-def $r14d, debug-location !17
+    Return implicit killed $r2d, debug-location !17
+
+...
diff --git a/llvm/test/DebugInfo/MIR/SystemZ/lit.local.cfg b/llvm/test/DebugInfo/MIR/SystemZ/lit.local.cfg
new file mode 100644
--- /dev/null
+++ b/llvm/test/DebugInfo/MIR/SystemZ/lit.local.cfg
@@ -0,0 +1,2 @@
+if not 'SystemZ' in config.root.targets:
+    config.unsupported = True